Synthesis of ionic liquid and its application in rubber

Synthesis of ionic liquid and its application in rubber modification and polymerisation Master’s Thesis Submitted by Manta Roy Roll No- 13RT60R01 Rubber Technology Centre I.I.T Kharagpur In fulfillment of the award of degree Master of Technology from Indian Institute of Technology Kharagpur, India & Leibniz Institute for Polymer Research, Dresden and Technical University Dresden

Honoured with DAAD Scholarship Under the supervision of

Prof. Nikhil K Singha Rubber technology Centre Indian Institute of Technology Kharagpur Kharagpur April 2015 India

Prof. Dr. Brigitte Voit Director and CSO Leibniz-Institut für Polymerforschung Dresden e.V and T.U Dresden Germany

Dedicated to my parents

Declaration

I certify that a. The work contained in this thesis is original and has been done by me under the joint supervision of Prof. Nikhil K Singha, I.I.T Kharagpur and Prof. Dr. Brigitte Voit, IPF Dresden, Germany. b. The work has not been submitted to any other Institute for any degree or diploma. c. I have followed the guidelines provided by the Institute in preparing the thesis. d.

I have conformed to the norms and guidelines given in the Ethical code of conduct of the Institute.

e. Whenever I have used materials (data, theoretical analysis, figures and text) from any other sources, I have given due credit to them by citing them in the text of the thesis and giving their details in references.

Manta Roy

Acknowledgement

I want to take this opportunity to show my gratitude to Prof. Nikhil K Singha, my Indian supervisor, I.I.T Kharagpur and Prof. Dr. Brigitte Voit, Director and CEO of Leibniz-Institut für Polymerforschung Dresden e.V (IPF Dresden) and Technische Universitӓt Dresden, Germany for their encouragement and guidance all through during this project work and introducing me in this field. I am grateful to Dr. Frank Bӧhme for giving his important suggestions and guidance all through my working days at IPF Dresden. I wish to acknowledge my heartiest indebtedness and gratitude to our honourable Head of Rubber Technology Centre, Prof. Dipak Khastgir for support and kindness by extending facilities and official support during my journey, Prof. Anil K Bhowmick for his strict guidance. I am thankful to all faculty members and non-teaching staffs of RTC for their help and cooperation. I would take the pleasure to shower my gratitude to Dr. Amit Das, Dr. Hartmut Komber, Mr. Marcus Suckow, Mrs. Liane Hӓuβler, Mrs. Kerstin Arnhold who all have supported with their helping hand and guidance throughout the journey to IPF Dresden. The warm friendship and support from my seniors and friends like Dr. Soumyadip Choudhury, Mr. Anand H, Mr.

Nabendu Pramanik, Mr. Prithwiraj Mandal, Mr. Arindam Chakraborty, Mr. Pradip Kumar Das and all the research scholars and friends of Rubber Technology Centre, is a great pleasure to record for their valuable help and encouragement. I am always grateful to my father Mr. Shyama Prosad Roy and mother Mrs. Sadhana Roy for their enormous and endless support in motivating me during this journey with a constant source of encouragement and moral support. I would like to acknowledge I would like to also acknowledge the financial support from DAAD, for financial support during my project in Germany. Above all I am thankful to Almighty God for giving me enough strength and good health

Date

Manta Roy

List of abbreviations BIIR

Bromo butyl rubber

IIR

Isobutylene-co-isoprene rubber

IL

Ionic liquid

PIL

Polyionic liquid

ATRP

Atom transfer radical polymerisation

CRP

Controlled radical polymerisation

RAFT

Reversible addition fragmentation chain transfer polymerisation

MADIX

Macromolecular design via interchange of xanthates

NMP

Nitroxide mediated polymerisation

CTA

Charge transfer agent

CNT

Carbon nano-tubes

IPN

Inter penetrating polymers network

RTIL

Room temperature ionic liquid

LCST

Lower critical solution temperature

UCST

Upper critical solution temperature

SWCNT

Single walled carbon nanotubes

NMR

Nuclear magnetic resonance

1

SN

2

Nucleophilic substitution unimolecular

SN CHI

Nucleophilic substitution bi-molecular [1-(6-chlorohexyl) imidazole]

BIM

1-butyl-3-methyl imidazole

DMSO

Dimethyl sulphoxide

CDCl3

Deuterated chloroform

DSC

Differential scanning calorimeter

TGA

Thermogravimetric analysis

MALDI-TOF

Matrix attributed laser desorption/ionisation time of flight

AFM

Atomic force microscopy

SEM

Scanning electron microscopy

FTIR

Fourier transform infrared radiation

SAXS

Small angle X-ray scattering

WAXS

Wide angle X-ray scattering

BMA

Butyl methacrylate

THF

Tetrahydrofuran

DHB

2,5-Dihydroxy benzoic acid

PMMA

Poly(methyl methacrylate)

CPBDT

2-cyano-2-propyl benzodithioate

CPDTC

2-cyano-2-propyl trithiocarbonate

PDI

Polydispersity index

AIBN

Azobisisobutyronitride

Abstract There have been spectacular advances in the field of research in rubber chemistry and technology after the introduction of supramolecular chemistry in rubber, since last decade. Ludwick Leibler had done the pioneering work in the development of smart rubber. This investigation reports the development of smart elastomers based on butyl rubber via the modification of bromobutyl rubber (BIIR) using an ionic liquid. IL is considered to be “green material” because of its negative vapour pressure, high thermal stability and eco-friendly nature. ILs is composed of organic cations based on alkyl imidazolium, alkyl pyridinium, alkyl ammonium and inorganic anions. Due to rapid advances in the field of chemistry and physics, PILs have attracted the materials scientists, as it is termed as potential “Green material” for future. It is a subclass of polyelectrolyte in which an ionic liquid (IL) species is present in each monomer repeating unit connected through a polymeric backbone to form a macromolecular. There has been a great interest in using ionic liquids as solvents for chemical reactions and polymerization reactions. They have wide range of glass transition temperature (Tg). PIL is used in modification of polymers leading to the development of new materials. Our aim of this investigation is to prepare a poly (ionic liquid)(PIL) based on imidazole via step growth polymerisation then modify a polymer by grafting the above PIL onto the polymer and to characterise the modified polymer and to study its morphology and thermal properties. It will be characterised by using NMR, FT-IR and mass spectrometer and thermal properties of the polymer will be evaluated by using DSC, TGA and DMA analyses. The morphology of the grafted polymer will be evaluated using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) analysis. The modified polymer can show interesting properties, like self healing characteristics.

KEY WORDS: Ionic liquid, Poly(ionic liquid), Modification of bromo-butyl rubber

Table of contents Page No. Chapter 1 Introduction and literature survey 1.1 Introduction 1.1.1 Ionic liquid 1.1.2 Polyionic liquid 1.1.3 Poly(isobutylene-co-isoprene)elastomer 1.1.4 Brominated (isobutylene-co-isoprene) rubber 1.1.5 Nucleophilic substitution of allylic bromine in BIIR 1.1.6 Vulcanisation of BIIR 1.1.7 Ionomer 1.1.8 Self healing polymer 1.1.9 Modification of isobutylene with substituted imidazole 1.1.10 Modification of BIIR with butyl imidazole Chapter 2 Experimental and characterisation techniques 2.1 Introduction 2.2 Materials required 2.2.1 Solvents 2.2.1 Chemicals 2.3 Instrumentation 2.3.1 Thermo HAAKE 2.3.2 Rheometer 2.3.3 Compression moulding 2.3.4 Characterisation 1

2.3.4.1 Nuclear magnetic resonance spectroscopy ( H NMR)

2.3.4.2 Fourier transforminfrared spectroscopy (FTIR) 2.3.4.3 Gel permeation chromatography (GPC) 2.3.4.4 Gas chromatography (GC) 2.3.4.5 Matrix assisted lazer desorption/ionisation time of flight mass spectrometry (MALDI-TOF-MS) 2.3.4.6 Differential scanning calorimetry (DSC) 2.3.4.7 Thermogravimetric analysis (TGA) 2.3.4.8 Scanning electron microscopy (SEM) 2.3.4.9 Hardness 2.3.4.10 Small angle x-ray sattering 2.3.4.11 Wide angle x-ray scattering 2.3.4.12 Electrical properties

1-29 1-3 4-6 7-8 8-9 10-11 12-14 15-19 20-24 24-25 26-29 30-37 30 31 31 32-37

Chapter 3

Synthesis of reactive imidazole derivative and its characterisation 3.1 Introduction 3.2 Preparation of imidazole based reactive monomer 3.3 Results and discussion 3.3.1 Characterisation 3.3.2 Optimisation of reaction condition 3.4 Conclusion

Chapter 4

Synthesis of asymmetric polyionic liquid based on reactive imidazole derivative 4.1 Introduction 4.2 Preparation of asymmetric polyionic liquid based on imidazole 4.3 Results and discussion 4.3.1 Characterisation 4.3.2 Optimisation of reaction condition 4.4 Conclusion Chapter 5 Utilisation of reactive imidazole derivative for modification of bromobutyl rubber 5.1 Introduction 5.2 Methods of ionic modification of BIIR 5.3 Results and discussion 5.3.1 Charaterisation 5.4 Conclusion Chapter 6 Application of Ionic liquid as solvent in RAFT polymerisation 6.1 Introduction 6.2 Method of polymerisation 6.3 Results and discussion 6.3.1 Characterisation 6.4 Conclusion Chapter 7 Summary and conclusion 7.1 Summary and conclusion 7.2 Future scope of work References

Page No. 38-49 39 39-40 41-48

49 50-62 51 52 53-61

62 63-90 64-65 65-66 67-90 90 91-105 92-94 95 96-105 105 106-109 107-108 109 110- 116

Chapter 1: Introduction and Literature Survey

Chapter 1 Introduction and Literature Survey

Page 1


1.1 Introduction Due to rapid advances in the field of chemistry and physics, polyionic liquids (PILs) have attracted the materials scientists, as it is termed as potential “Green material” for future. It is a subclass of polyelectrolyte in which an ionic liquid (IL) species is present in each monomer repeating unit connected through a polymeric backbone to form a macromolecular. Ionic liquids (IL) are organic salts that are liquid at ambient temperature. ILs are composed of organic cations are based on alkylimidazolium, alkylpyridinium, alkyl ammonium and inorganic anions. There has been a great interest in using ionic liquids as solvents for chemical reactions in polymerisation and also in the modification of polymers. The ionic moieties used in modification of polymers will impart non-covalent interaction resulting in dynamic reversible bond formation. The ionic groups will form ionic clusters within the matrix and will enhance the mechanical properties and self-healing property. Till date there have been spectacular advances in research in rubber chemistry and technology after the introduction of supramolecular chemistry in rubber since last decade. Ludwik Leibler has been pioneer in this development of rubber science.

1.1.1 Ionic liquids Ionic liquids are materials that are composed solely of cations and anions. The cations are pyridinium based, imidazolium based, phosphonium based, ammonium based IL [1]. The anions used are Cl-, AlCl4-, PF6-, BF4-, NTf2-, DCA-, SCN-, Br-, CH3COO-, CH3SO3-, N3- etc. Some examples are given in Figure 1. At room temperature it exists in liquid state as well as in ionic form while the other solvents like toluene, chloroform, hexane, dimethylsulfoxide etc. exists as non-ionic part and exists as molecules [2]. The liquidity behaviour of ILs over wide range [3,4] is due to not so close packing structure [5]. Due to this reason they have a wide range of glass transition temperature (Tg), varying from low to higher values [6,7]. The liquid range varies from -96 °C to 400 °C. They are non-volatile, thermally and chemically stable, mechanically stable and viscous [8]. They are eco-friendly, non toxic, non flammable. PILs are permanent and strong electrolytes [9,10]. They are deflected by electric field. They are moderate to poor Page 2


conductors of electricity. PILs are soluble in several organic solvents, from polar to less polar, depending on the chemical nature of the PILs. Solubility of ionic liquids varies depending upon the anion and cation used [11]. R R R

R' N

N

R

R R'''

N

R'

R'

P

F C F

O S

R'''

Br

SCN

NO3

R''

R''

F

N

N

N

O O

N

N

3FC

O2 S

N

O2 S

CF3

Figure 1: Different cations and anions in ionic liquid. They have good solvating properties for a range of polar and non-polar compounds. Ionic Liquids have been considered as “green solvents” [12,13] and are also known as “designer solvents” [14] as their characteristics can be tailored by changing the cationic and anionic part. Depending on the length of the alkyl chain attached to the cationic moiety, the hydrophobicity and hydrophilicity of ILs can be tailored [15] which increases with increasing length of the alkyl chain. Pyridinium based ILs are very novel compared to the imidazolium based ILs [16,17]. Phosphonium based ILs is much more stable than imidazolium or pyridinium based ILs. Imidazolium based ILs attracted great attention because of their stability under oxidative and reductive conditions, humidity [18,19], their low viscosity [20], and their ease of synthesis. Imidazolium-based ILs has been used as catalysts for the improvement of reaction time, yield and chemo selectivity of many organic reactions. They are used as solvents for Page 3


Friedel-Crafts reactions [21], Grignard reactions, and also in the field of Diels Alder Reactions [22]. With thermal stabilities up to 400 °C, they can be used for hydroformylation reactions [23,24] Heck reactions [25] etc, where the reactions are carried out above 150-200 °C. Phosphonium based ILs has good stability towards bases, hence, they can be used for synthesis in basic media. ILs can dissolve enzymes, hence, they can be used in bio medical applications for bio polymer synthesis and drug delivery systems [26,27]. ILs may have a broad field of applications like as non toxic solvent for synthesis, catalysis, extraction, cosolvent in battery, lubricant, additives in synthesis of nanoparticles, polymerisation, analytical chemistry, azeotropic estimation, separation of alkali earth metals, azeotropic mixtures, carbon dioxide purification [28] etc. It acts as a novel solvent because of its eco-friendly behaviour, recyclability of the solvent, reuse, and concerning the environment [29-30].

1.1.2 Polyionic Liquid (PILs) Poly (ionic liquid) is known as polymerized ionic liquids. PILs are solid at room temperature. It is a subclass of poly electrolytes in which an ionic liquid (IL) species is present in each monomer repeating unit connected through a polymeric backbone to form a macromolecular architecture. Similar to ILs, PILs generally consist of bulky nonsymmetrical organic cations (such as an imidazolium pyridium, ammonium, or phosphonium cation) together with various organic or inorganic anions, displaying unique properties such as extremely low vapour pressure, non-flammability, high polarity, high thermal stability, favourable electrochemical properties, and unorthodox and tuneable miscibility behaviour [31]. PILs are permanent and strong electrolytes. They have wide range of glass transition temperature (Tg), varying from low to higher values [32]. Liquid PILs, free of unsaturated groups are known to be deflected by the electric field. PILs are soluble in several organic solvents, from polar to less polar, depending on the chemical nature of the PILs. Anions play an important role in determining solubility of PILs. PILs with cationic backbone are more soluble in different solvents. Most PILs are not soluble in water but in polar organic Page 4


solvents. This is mainly due to the hydrophobic character of the counter-ion and the reduced columbic interactions. There are various ways of preparing PILs. The most common synthetic approach uses the chain growth polymerisation methods. Vinyl monomers (Figure 2) bearing imidazolium moiety is homopolymerised and copolymerised with conventional vinyl comonomers based on styrene, (meth)acrylate and (meth)acryl amide etc via free radical polymerisation, controlled radical polymerisation (CRP), ionic polymerisation or via coordination polymerisations. It has been observed that Atom transfer radical polymerisation (ATRP) and Reversible addition fragmentation chain transfer (RAFT) polymerisation are very useful for synthesizing PIL block copolymers [33]

N

X N

R

Figure 2: Imidazole

derivative Depending upon the anionic size, the glass transition temperature of the polymer and ionic conductivity can be modified. PILs expand the properties and applications of ILs and common polyelectrolytes. Rapid advances in the chemistry and physics of PILs have attracted the materials scientists, as it is termed as potential “Green material” for future [34]. The preparation and study of PILs is to harness the potential for the field of electrolytes and fuel cell. It is known to be predicted that this eliminates the disadvantage of leakage, flammability, toxicity and instability. PILs combining the unique properties of ILs with increased mechanical stability, improved process ability and more complex self-assembling ability of polymeric materials. The polyelectrolyte is used as dispersing agents or stabilizers in chemical processing, hence this criteria leads to have the application in the field of medicinal field. Page 5


Recent studies reveal that surface-fictionalization of carbon-annotates (CNTs) with PILs as a metal nanoparticle catalyst supports the fuel cell use [35]. PILs have shown beneficial towards the preparation of porous polymers and microparticles from IL monomers through heterogeneous polymerisation (emulsion or suspension). Muldoon and Gordon reported the first preparation of poly (IL) microparticle. And according to his research he concluded that PIL microparticle behaves as an immobilized matrix along with the benefits of activation of embedded enzyme [36]. From the recent study of Ohno and his co-workers on PILs reveals that ionic liquids show self-assembling tendency which leads to form functional material, that are used in nanolithography, drug delivery, nanoelectronics and optoelectronics. The amphiphilic self-assembled structure has higher order of nano and meso structures [37]. Another major field of application of PILs involves the preparation of ionic electroactive polymers by combining ionic transport inherent structures to the ionic liquid which will have electrical conductivity afforded with an electro active group. This work has been carried out by Naudin et al. An example of such type of polymer is benzylthiophene derivative of imidazolium group. In spite of lots of work done in the field of synthesizing ionic liquid matrix (ILM) based on imidazolium cationic moiety but now it has drawn the attention of lot of researcher towards the introduction of polymerisable moieties like ammonium, pyrrolidinium. While these studies are applicable for the preparation of diblock copolymers, it has also been used in making interpenetrating polymer networks (IPN) consisting of two synthetic polymers or one synthetic and other natural polymer. As for example: imidazolium ILM containing vinyl and styryl moieties are used to solubilise cellulose, a polysaccharide and hence it could be polymerized to form poly(IL)-cellulose-IPN [38]. Thus it can be concluded that inorganic-organic composites produce functional materials with better mechanical properties, thermal stability etc. with the properties of ILs. A recent inorganic-organic composite has been prepared with an imidazolium cation functionalized with triethoxysilane.

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Thermal stability and melting point depend on the liquid's components. Various thermally stable RTILs (Room temperature ionic liquid) are available. The upper limits of thermal stability of ionic liquids reported in the literature are usually based upon fast (about 10 °C/min) TGA scans, and they do not imply long-term (several hours) thermal stability of ionic liquids, which is limited to less than 250 °C for most ionic liquids. The solubility of different species in imidazolium ionic liquids depends mainly on polarity and hydrogen bonding ability. Saturated aliphatic compounds are generally only sparingly soluble in ionic liquids, whereas olefins show somewhat greater solubility and aldehyde can be completely miscible. PIL is used as additive in polymer processing. It is used as an important component in polymer electrolyte and in specialty polymer gels. It is used as templates for porous polymers, and novel electrolytes for electrochemical polymerisations [39]. PIL is also used in modification of polymers leading to the development of new materials. Apart from all these characteristics, lower critical solution temperature (LCST) type phase transition is a distinctive phenomenon of the PILs that has been widely utilised to produce stimulus-responsive or “smart” materials. Seno et al. reported that vinyl ether polymers with imidazolium or pyridinium salt pendants underwent sensitive LCST-type phase separation in organic media. The same group also observed an upper critical solution temperature (UCST)-type phase separation of the same vinyl ether polymers with imidazolium tetrafluoroborate salt pendants in aqueous solution. Due to very high thermal stability, and powerful solvation capability they can be used directly as a catalyst to accelerate the reaction kinetics. PILs have exhibited great potential as DNA vectors [40], providing a pathway for the design of novel gene vectors with high efficiencies and good opportunities for the development of IL based materials in biomedical applications. From very recent study of Jin et al. developed a hybrid sensor based on PIL wrapped single walled carbon nanotubes (SWCNTs) and utilised it for detection of CO2 [41].

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1.1.3 Poly (isobutylene-co-isoprene) elastomer Butyl Rubber (IIR) is a copolymer of isobutylene (98%) and a very small fraction of Isoprene units (1-2.5%). IIR has been commercialized in the year of 1943. Synthesis of IIR involves the copolymerisation of isobutylene and isoprene through a carbocationic polymerisation method. The polymeristion is carried out at lower temperature (-90 °C to 100 ° C). The reaction is highly exothermic. The reaction is initiated with various Lewis acids. The molecular weight of butyl rubber can be controlled by controlling the initiation and chain transfers so that the glass transition temperature resides below -68 °C [42]. The main advantage of the butyl rubber is its excellent air impermeability, good flex properties due to the lower concentration of the unsaturation present in the rubber, good thermal stability and oxidative stability along with very good moisture barrier and chemical resistance properties. Due to all these properties it has got broad application in making the inner tube tyre (shown in Figure 2) and also due to its good adhesive nature it can be easily bonded to the inner metallic layer of the tyre. The characteristic of good adhesion at lower temperature, with good traction and acceptable rolling resistance makes it widely acceptable in the manufacturing of inner tubes of tyre and tyre treads. But it has poor wear resistance, abrasion resistance due to limited availability of Van der Waals interaction with carbon black and other fillers, due to which it has limited application in making tyre treads [43].

Figure 3: Inner tube tyre tube Page 8


1.1.4 Brominated poly(isobutylene-co-isoprene) The polymerisation process of halobutyl is exactly same as non-halogenated rubber. Prior to making of halobutyl rubber, at first IIR is made soluble in solvents like hexane, chloroform etc. Then bromination of the butyl solution is done in highly agitated reaction vessel. During the preparation of halogenated IIR, one mole of hydrobromic acid is released which is neutralised with caustic soda (NaOH). The halogenation of IIR makes the rubber much more suitable for the use of inner liners of tyre and tubes. As the introduction of the more polar group (bromo group) in butyl rubber increases the adhesive nature of the rubber and makes it more air impermeable. Hence BIIR is important for industries. Hence the microscopic structures of bromobutyl rubber have been investigated from NMR spectroscopic study. It exists as Z and E endomethylene strctures, exomethylene groups [44]. The study of Ho and Guthmann reveals that the predominant isomer for BIIR is kinetically-favoured exo-(methylene) isomer rather than E,Z-endo( bromomethyl) isomer [45] (shown in Figure 4.1-4.3)

Exomethylene isomer m

Br

n

Figure 4.1 Br

Z- bromomethyl isomer n H

m

Figure 4.2

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Br

H

E-bromomethyl isomer n m Figure 4.3 Figure 4.1-4.3: Different isomers of BIIR.

1.1.5 Nucleophilic substitution of allylic bromide in BIIR Regarding the previously discussion, bromination of butyl rubber leads to increase the rate of reaction with sulphur during vulcanisation. Hence this possibility leads to the development of nucleophillic substitution reaction that can be carried out with BIIR. We are familiar with two types of nucleophilic substitution reaction: SN1 and SN2. The nucleophillic addition takes place at the δ-carbon atom (less sterically hindered carbon) leading to the formation of double bond with the elimination of hydrogen bromide [46]. Approach towards this substitution is based on SN2 pathway. The mechanism is shown in Scheme -1:

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Scheme 1: Nucleophilic substitution reaction in BIIR. The mechanistic pathway for the nucleophilic attack at the exomethylene carbon atom in BIIR proves that exomethylene isomer is dominating with its α-carbon atom being the most sterically hindered carbon atom. It shows the isomerisation through SN2 mechanism with the release of hydrogen bromide and the bromine group isomerises to the allylic position [47]. The ionic bonding is formed through this halogen bearing δ-carbon atom. The mechanistic pathway of the approaching monomer with the exomethylene isomer of BIIR bearing halogen atom at δ-carbon atom is shown in Scheme 2: Steps: The bromine atom at the δ-carbon atom is tautomerised to form an exomethylene isomer of BIIR. Then the approaching monomer is grafted to the polymeric backbone of BIIR through the halogen bearing carbon atom in BIIR forming an ionic moiety.

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Br

-HBr

Br

N N

Cl

Br N N Cl

Scheme 2: Ionic modification of BIIR.

1.1.6

Vulcanisation

of

brominated

poly(isobutylene-co-

isoprene) The method of vulcanisation of natural rubber with sulphur was first introduced by Charles Goodyear and commercialized in 1841. Vulcanisation of rubbers has been introduced in order to prevent creeping behaviour of rubber, to increase its mechanical properties like tensile strength, modulus, elasticity, strength to with hold applied stress. Vulcanisation is a process by which elastomeric materials or rubbers are converted into a Page 12


three-dimensional network by binding together independent chain molecules. Uncured rubber is soft and cannot withstand any applied stress, shows creep behaviour but vulcanisation provides improvement in properties as the chains of each polymer/rubber is hold with the curing agents through covalent bond formation. Vulcanisation reduces the flow of elastomeric material and the amount of permanent deformation after removal of the deforming force. Vulcanisation of the elastomer is done by using various curing agents. There are various curing systems like conventional curing system, efficient vulcanisation system, semiefficient vulcanisation system. Various curing agents are used like sulphur curing system, quinone dioxime cure, sulphur monochloride curing, resin curing, magnesium chloride curing etc [48]. The different types of curing systems depend on the type of structure of the elastomeric chains and presence of activating groups and unsaturation present. Rheological study of the vulcanised rubber has attracted an attention of the rubber technologists. To determine the curing temperature of the sample, rheometers are used, in which the disc is an oscillating one. There are two discs: lower disc and upper disc. The lower disc is attached to the motor which rotates in sinusoidal pattern while the upper disc is attached to torque transducer that helps in capturing the torque and gives rise to phase shifts of two signals. From a rheometric graph, the storage modulus (G*), loss modulus (G”), and complex viscosity (η*) can be determined. A typical graph will be shown in this method which will provide the scorch time, curing period where the graph will show the formation of crosslink within the material and hence gains the strength of the material. But the other part of the graph will show the over curing period which will lead to detoriation (reversion cure), marching cure or normal cure. This can be well explained from the diagram given below. The reversion curing leads to breaking of the crosslink as well as chain scission which leads to loss of molecular weight. The marching cure increases the number of crosslink that leads to increase in the molecular weight. The area under torque versus time graphs represents the area of under cured and over curing characteristic of the elastomer. Over curing region includes the marching, plateau and reversion behaviour. And curing region includes the optimum curing and under vulcanisation of the elastomer. The following graph shows the curing behaviour of the elastomer shown in Figure 5. Page 13


Rheometric graph: The rheological analysis is done in rheometer where the curing behaviour of the specimen (compounded elastomer) is studied at various temperatures. The rheometric curve can be of three types marching behaviour, plateau and reversion (shown in Figure 6-8). The marching behaviour is due to the increase in molecular mass and crosslink implying a improvement in the mechanical property. Plateau behaviour implies the constancy of the mechanical properties and tends to achieve the highest curing stage. Reversion takes place due to the breakdown of the covalent crosslinked bond leading to the detoriation in the mechanical properties. The rheograph is illustrated below is shown Figure 5.

Figure 5: Rheological curve

Reversion Plateau leads to chain scissoring and leads to deterioration of the mechanical properties shown in Figure 6.

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Figure 6 Chain scission Marching leads to extra crosslink and increase in molecular weight.

Figure 7 Extra crosslinking taking place

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Unvulcanised Rubber Molecules Rubber Molecules

Sulfur

crosslinking Rubber

S

Vulcanised Network Figure 8: The Flow Chart of unvulcanised rubber converting into vulcanised rubber. (Conventional vulcanisation)

1.1.7 Ionomers An ionomer is a polymer that comprises repeat units of both electrically neutral repeating units and a fraction of ionised units (usually no more than 15 mole percent) covalently bonded to the polymer backbone as pendant group moieties [48]. This means that most ionomers are copolymers of the neutral segments and the ionized units, which usually consist of carboxylic acid groups. The classification of a polymer as an ionomer depends on the level of substitution of ionic groups as well as how the ionic groups are incorporated into the polymer structure. Ionomers have unique physical properties including electrical conductivity and viscosity increase in ionomer solution with increasing temperatures. Ionomers also have unique morphological properties as the nonpolar polymer backbone is energetically incompatible with the polar ionic groups. As a result, the ionic groups will micro phase separate into ionic rich domains in most ionomers. Ionomer synthesis consists of two steps: firstly the introduction of acid groups Page 16


to the polymer backbone and the neutralization of some of the acid groups by a metal cation. Groups introduced are already neutralized by a metal cation. The first step (introduction of acid groups) can be done in two ways; a neutral non-ionic monomer can be copolymerised with a monomer that contains pendant acid groups or acid groups can be added to a non-ionic polymer through post-reaction modifications. Small amounts of ionic functionality bound to polymers of low dielectric constant (such as BIIR) can affect the properties of the materials. Since the backbone is a non-polar backbone which can’t solvate the ionic groups. So there will be an aggregation of ionic pairs [49]. These aggregated ionic pairs will form a network that behaves like dynamic vulcanisates. The ionic pairs are held together with the ionic interactions in the backbone of non-polar polymer/rubber. Due to the introduction of the ionic groups there will be a better interaction with the carbon black with the ionic groups. Several studies reveal that higher degree of reinforcement is observed when these ionomers are treated with precipitated silica and montmorillonite clay. But as these vulcanisates are dynamic in nature hence, these ionic crosslink is disrupted when exposed to plasticisers at elevated temperatures which limits its reprocessability and they show creep when exposed to large strain. There are two methods of making ionomers: copolymerisation of a non-polar monomer with low level of functional monomer and post–polymerisation modification. Postpolymerisation is best for lower functionality monomers and hence most beneficial for butyl rubber as it is non-polar in nature and incompatible with ionic/polar monomers. Previous studies has been done on butyl rubber in making butyl rubber based ionomer with tertiary amine, triphenylphosphine, imidazole, butyl imidazolium based ionomers. A distinguished study can be done between ionomers, starting monomers and vulcanisates with the help of rheological study [50]. If there is an increase in the storage modulus observed in the material then it can be suggested that the material is not tough and stronger, it may be due to the reason of possibility of crosslinking or of ionomer formation. To justify the ionomer formation, solution viscosity study along with small angle diffraction study can be beneficial. Crosslinked material will have higher viscosity than original polymer chain due to the swelling of the covalent links in the polymeric Page 17


coil. But on the other hand the ionomer will have lower viscosity because there are no intermolecular polymeric interactions and have small hydrodynamic radius. Hence the chains will aggregate towards itself rather than towards the solvent. The solution viscosity will increase with increase in the ionic content that is greater than the critical concentration, whereas for non-ionomers it will increase more gradually. The ionomers can be best determined with the help of small angle scattering rays. When a beam of x-rays falls on a small sample of the materials, some part of the rays are scattered which are captured in the detectors while the undistorted rays are captured in the beam stop. The scattered beam of x-rays will help to predict and determine the size and shape of the sample. So SAXS study is the only technique that helps in the determination of the multiplet size in the polymer matrix, otherwise the bulk polymer will show no deflection in the x-ray diffraction. According to the study of core shell model, it was assumed that there is a core of ion pairs (multiplet) that is surrounded by a small section of low electron density covered with higher electron density creating a lamellar structure as proposed by Roche et al [51]. According to the study of Einsberg, Hird and Moore, the mobility of the ionomers are restricted due to the higher aggregation of ionic pairs leading to increase in molecular weight, which causes a crowding of chains. Therefore due to the restricted mobility of the chains they are assumed to have higher glass transition temperature [50]. Ionomers have two distinct Tg. However for low ion content such as BIIR ionomers there will be a broad range of glass transition temperatures instead of two distinct peaks as because there will be lesser multiples formed hence lesser will be the restriction in chain mobility. At higher concentration of ionic content, the elastomers have all restricted mobility region leading to only one distinct glass transition temperature (shown in Figure 9).

Page 18


Figure 9: Ionomer According to the study of Tant and Wilkens they have investigated a class of ioncontaining copolymers in which the ionic groups is made up of more than 15 mol%. According to Eisenberg and Rinaudo, ionomers are polymers whose bulk properties are determined in the polymer structure within discrete areas by ionic interactions. The synthesis of the ionomer is generally done in two ways: [23] 1. Direct Synthesis: copolymerization of a functionalized monomer with an olefin unsaturated monomer. 2. Post polymerisation and modification an existing saturated polymer. The ionic interactions in ionomers are usually electrostatic interactions between anions and cations. Although the elastomeric ionomers have been known for over 40 years, they have little commercial application. When small amount of ionic functionalities are attached to polymer with low dielectric constant, they will drastically affect the material properties. Since the non-polar hydrocarbon backbone, the ionic components cannot solvate ions significant aggregations can be expected. Eisenberg hence defined the multiplet as a unit, which consists of several ion pairs whose number is limited by steric hindrance caused due to the adjacent chain segments and size of the ion pairs. After the STM model (Eisenberg - Hird -Moore), the polymer chains are anchored by their nationals ion pairs of the multiplet (shown in Scheme 3).

Page 19


Scheme 3: Representation of the reduced ionic mobility in poly (styrene-co-sodium methacrylate) ionomer. (Ref. - Eisenberg et al. 1990)

Page 20


1.1.8 Self healing polymers The first word about self-healing elastomer was given by Ludwik Leibler [52]. The great scientist was the first who introduced the concept of self-healing elastomers. He concluded that when the rubber strips were cut into two pieces and then brought close to each other, these two strands of rubber get bonded again without any application of external force, heat or energy. According to his views, conventional rubber is made of a single, continuous, stretchy molecule, held together with strong chemical links called covalent bonds. Once these bonds are cut by a break in the material then the rubber can’t be reassembled. But if some fatty acids are introduced in urea then there might be some force of attraction with the nitrogen atom and the hydrogen atom just like that of the presence of the bond in water. These types of forces are not covalent in nature, hence they are not hard enough to withstand toughness and stress a lot. But these types of forces are responsible for the self-healing characteristics in the elastomer. These groups are very non-uniformly arranged and hence it does not lead to give rise to crystallinity of the polymers. That is why Leibler performed the experiment by cutting the elastomer into two halves where the bond is broken between the protruding groups, but due to presence of their own attractive forces, the groups are brought close to each other and again the reassembling of the elastomer was taking place. So because of his outstanding and admirable contribution with this excellent ideas leads to the new generation of selfhealing elastomer. But the drawback of the elastomer prepared by Leibler is this elastomer shows creep behaviour when exposed for long time. So till that time all the elastomeric compound were exposed to crosslinks in order to achieve a better mechanical properties like tensile strength, modulus etc. But after the introduction of such type of reversible crosslinks in the history of elastomer, it has drawn the attention of most of the researchers working in this field. And hence till now lots of works has been performed till now. Once Leibler and his co workers worked on self healing elastomer with the concept of forming supramolecular assembling of the ionic

Page 21


group which will lead to the thermo reversible and self-healing property [53] (shown in Figure 10)

Figure 10: Self-assembling of smart material (Ref. Leibler et al.)

In another work of Leibler, they introduced the amine group with the carboxylic acid group leading to the formation of the amide chain which will lead to the self-assembling characteristics of the polymer due to the formation of the hydrogen bonding (shown in Scheme 4). And hence due to this presence of hydrogen bonding the bonds of the elastomers can be made reversible and hence it may lead to the reuse and recycling of the polymeric material with showing of little creep. They are liquid at room temperature. And they can play with the glass transition temperature with the introduction of plasticisers or other modification of the functionality of the fatty acids, which will lower the glass transition temperature. Hence this concept has become a challenging field of work for the researchers as well as for the industries. Page 22


Scheme 4: Hydrogen bonding showing self-healing property. (Ref. Leibler et al.)

So after this exceptional and innovative idea of making dynamic bonding with the help of hydrogen bonding, a lot of work has been done by Leibler in this field by using various fatty acids and their interaction with the amide groups (shown in Scheme 5). According to the ideas of Leibler, the dynamic bond can be formed not only with the help of ionic interaction of the ionomers but also can be formed with the help of hydrogen bonding [54]. So this novel idea leads to many innovative investigations about such possibility of dynamic uncrosslinked bonding. Followed with this idea, the concept of introduction of the ionic groups came into the mind of the researchers which may also lead to some dynamic interactions resulting in self healing characteristics. It was supposed that after deterioration of the surface of the tyre if such an auto-generated self healing property can be observed where the surface

Page 23


will get healed up by itself rather than applying any external factors like temperature, force etc.

Scheme 5: Schematic diagram showing the interaction through hydrogen bonding. (Ref. Bao et al. 2013) At the early stages of the research in this field, some researchers have investigated the nature of bonding of BIIR with imidazole which leads to the formation of the crosslinking through the interaction of the two nitrogen atoms with allylic bromine group in BIIR as shown in Figure 12. Page 24


N

Br N

Figure 12: Imidazole crosslinked BIIR Then in order to prevent the crosslinking and form only ionic groups interactive, alkyl imidazole is introduced with the BIIR, where there is formation of alkyl imidazolium bromide-grafted-BIIR which shows the ionic interactions and thermo-reversible bond formation leading to the contribution in the field of self healing characteristics due to repeated dynamic interaction of the ionic groups [55] (shown in Scheme 6). Ionic Interacting Groups

Ionic Bonding

Ionic charges interacting with each other

Scheme 6: Ionic interaction showing self-healing behaviour. (Ref. White et al. 2011) Page 25


Due to the presence of the opposite charges present within the matrix, there is the presence of the ionic interactions within the matrix leading to the self healing property. But as we are moving forward to avoid crosslinking hence this type of interaction is predicted to form a dynamic bond, which may degrade at very higher temp, but again it can heal by itself at moderate conditions without any external force, temperature, or pressure. This interesting property leads to many investigations with butyl rubber due to its higher content of unsaturation. And there is the improvement in properties not only the self healing property but also regarding the mechanical properties like tensile strength, torque, hardness, modulus, tearing strength etc. The aim of modification of butyl rubber or bromo butyl rubber has been a great importance as it contains the unsaturation group of isoprene unit up to 2.5 ± 0.5% and hence it has the possibility of further bond formation or grafting of any functional groups into this unsaturation unit. Hence, this idea lead to the formation of modified butyl rubber with some improved mechanical properties which is spectacular inspire of not being crosslinked but this type of ionic interactions lead to the formation of dynamic bonding which shows the mechanical properties like cross linked elastomer. Hence, this type of modifications reduced the possibility of crosslinking the elastomers and are re-usable and reproducible after repeated usage. Still investigations are going on to overcome this irreversible crosslinking and to generated green chemistry.

1.1.9 Modification of isobutylene with a substituted imidazole to form imidazolium functionalized BIIR A recent study has been carried out by Bandana Talukdar under the supervision of Prof. Anil K Bhowmick [56] where they have made imidazole modified isobutylene (shown in Figure 13) which has proved its improvement in the mechanical properties as well as the barrier property. So this type of modification has proved to impart its unique property when grafted onto the elastomeric backbone. The modified ionic polymer displayed greater thermal stability, greater flexibility, improved tensile strength, and higher barrier

Page 26


properties compared to the unmodified BIMS. A 1.8-fold increase of elongation at break was achieved with 1.18 mol % (3.1 wt %) of modification.

CH3 C H2

CH3 H2 C

C

H C

H2 C

C

CH3

CH3

N

Br N

Figure 13 Modified bromobutyl rubber. (Ref. 56)

1.1.10 Modification of bromo-butyl rubber with butyl imidazole

Mechanical properties

In this study of modification of BIIR with butyl imidazole [57], there is an increase in the mechanical property and the tear fatigue property also increased in case of ionically modified BIIR rather than covalently crosslinked BIIR (shown in figure 14). And at a grafting percentage of 75% there is an indication of self-healing property, which proved beneficial during the study of ionic non-covalent interaction. The modification of BIIR with butyl imidazole is shown in Figure 14

N

N

*

*

Figure 14

Page 27


From the above mentioned study, it is revealed that the modification of bromo-butyl rubber has shown a comparable improvement in the torque as compared to the pure BIIR. In the rheological study it is revealed that there is a marching behaviour resulting in the improvement in the molecular weight due the formation of ionic interactions within the elastomeric matrix. And the torque value is even higher than sulphur cured BIIR, where plateau region is achieved. Thus it can be concluded that with modification of BIIR, we can get higher tensile strength, tear strength and even hardness is comparable with sulphur cured vulcanisates. But with the help of modification of BIIR, we can avoid crosslinking and can make the vulcanisate recyclable, reusable and uncross linked. From study of dynamic mechanical property, it can be observed that BIIR has a wide glass transition temperature range. The shoulder is observed at around -50 °C which is expected to be due to low temperature process or branches of BIIR or bromine group present. At around 60 °C there is another small transition shown which is predicted to be due to the formation of ionic clusters. At higher temperature, it is observed that pure BIIR started to flow, but the modified BIIR (BIIR+BIM) is stable along with sulphur cured BIIR as compared to pure BIIR. Hence, we can expect of better mechanical properties as compared to Pure BIIR and the mechanical properties are comparable and even better than covalent crosslinked BIIR.

Motivation Thus from all the above mentioned results and observations it can be concluded that any type of modification leading to dynamic bonding with BIIR may result in comparable and spectacular results than covalently crosslinked BIIR. Hence, in order to an approach towards green chemistry, several projects are carried out investigating the possible condition and probability of forming dynamic bonding rather uncrosslinked linkages with BIIR and even other elastomers like neoprene, hypalon etc. can show such ionic interactions through the linkage with the halogen bearing carbon atom, as a result such bonding may result in dynamic reversible bonding.

Page 28


Objectives of current study The aim of this study is to synthesise an asymmetric imidazole based monomer, characterise it with 1H NMR study and then finding an optimum condition to polymerise it and form an asymmetric poly (ionic liquid) chain having imidazole at one end and bromine group at the other end. While performing this reaction, special care is to be taken to prevent early polymerisation. Then modification of BIIR with this synthesised monomer will be done under optimised condition to have maximum grafting. The aim of the modification is to develop a smart rubber via this modification of BIIR with ionic liquid. Then this modified BIIR will be characterised with 1H NMR, FTIR and its mechanical properties and self-healing property will be investigated. And also to use ionic liquid as the solvent for RAFT polymerisation, a controlled polymerisation.

Page 29

Chapter 2: Materials and Methods

Chapter 2 Materials and Methods

Page 30


2.1 Introduction This chapter reports the detailed information about the sources, purification technique used during the thesis work. This chapter also deals with the different characterisation techniques and different instruments used to characterise the monomers, polymers and modified elastomer. The details of the methods used to study the mechanical, thermal, morphological study of the polymers are described in this chapter.

2.2 Materials required Butyl

methylacrylate

(BMA),

1-Butyl-3-methylimidazolium

hexafluorophosphate

(BMIHFP) was purchased from Sigma Aldrich, USA. The RAFT reagents, 2-cyano-2propyl-benzodithioate (CPBDT), 2-cyana-2propyl dodecyl trithiocarbonate (CPDTC) and thermal initiator azo-bis isobutyronitrile (AIBN) were also purchased from Sigma Aldrich, USA and used as received. Imidazole (Sigma-Aldrich), 1,6-dibromo hexane (Sigma-Aldrich), 1-bromo-6-chloro hexane (Sigma-Aldrich), sodium hydride (SigmaAldrich), dichloromethane, diethyl ether were used without further purification.

2.3 Instrumentation 2.3.1 Thermo HAAKE Specifications   

Rheo OS Rheo Drive 7 PolyLab 300p System mit HAAKE Rheomix 600p Banburry Rotor R 600 Speed – 501/minute

Page 31


Figure 17 HAAKE Rheo Mix In the HAAKE internal mixer the mixing and proper dispersion of additives with the elastomer is performed at certain conditions depending upon the necessity. In this HAAKE Rheo mix Banbury blades R 600 is used for mixing of the ingredients along with elastomer.

Page 32


2.3.2 Rheometer This is a dynamic rheometer (SCARABAEUS SIS V50, based on DIN 53529) for isothermal and non-isothermal measurements at variable frequency and amplitude as shown in Figure 18 is used. The various curing behaviour of the compounded elastomer is studied with optimising the vulcanisation conditions.

Figure 18 Rheometer SCARABAEUS SIS V50

After getting the optimum curing temperature the compounded samples are put into a pre-heated mould of any dimension and thickness to get a cured sheet after being crosslinked. Then the specimens are taken for further characterisation.

Page 33


2.3.2 Compression Moulding The curing of the elastomer is done in this compression moulding machine. Before pressing the samples, in order to improve the homogeneity of the mixture and the process flow using a laboratory mill type ( Polymix 110L ) from Servitec the mould is pre-heated at 35°C and then the sample is put for moulding into thin sheet. The compression moulding machine is shown in figure 19.

Figure 19 Compression Moulding machine

2.4 Characterisation 2.4.1 Nuclear Magnetic Resonance Spectroscopy 1

H NMR analysis was carried out using NMR spectrometer DRX 500 (Bruker) at a

frequency of 500.13 MHz (proton) spectrometer using CDCl3 and DMSO-d6 as a solvent.

Page 34


2.4.2 FTIR Spectroscopy The FTIR spectra of the samples are measured by means of Vertex 80v (Bruker) with a Golden Gate Diamond ATR unit (SPECAC) attached with a MCT detector. The measurement range is 4000-600 cm-1 and 100 scans per run. Resolution of spectra is 4 cm-1. Baseline correction was also carried out. 2.4.3 GPC Analysis GPC analysis was carried out in at ambient temperature on a Viscotek GPC instrument (model VE 3580), equipped with refractive index detector. The polymer solution was passed through two ViscoGel GPC columns (model GMHHR-M 17392) having pore size 30–650 Å connected in a series. Tetrahydrofuran (THF) was used as an eluent with flow rate of 1.0 mL for 25 min to complete each run. The narrow dispersity poly(methyl methacrylate) (PMMA) was used as a calibration standard. Data analysis was performed using Viscotek OMNI-01 software. 2.4.4 Gas Chromatography (GC) Analysis The conversion of polymerization of BMA in equilibrium with RAFT reagent in presence of Ionic liquid was carried out using Agilent GC instrument. IL has very high boiling point so it can’t be separated from the polymer gravimetrically. Hence, the % of conversion of the polymerization was calculated using GC analysis. During GC analysis the injection temperature maintained at 150 °C and the detector temperature maintained at 250 °C. 2.4.5 MALDI-TOF-MS MALDI-TOF-MS analysis of polymer sample was performed on a Perceptive Biosystems Voyeger Elite MALDI-TOF mass spectrometer, equipped with a nitrogen laser (k 5 374 nm). 2,5-Dihydroxy benzoic acid (DHB) and sodium trifluoroacetate were used as a matrix and cationic agent respectively for this experiment. The THF solution of

Page 35


polymer, matrix, and cationic agent were mixed at 10:10:1 volume ratio. All the spectra were averaged over 130 laser shots. 2.4.6 Differential Scanning Calorimeter (DSC) DSC analyzed data was recorded using a TA instrument (DSC Q 1000 Advanced Tzerro TM Technology) at a temperature range of -80 °C to 400 °C at a heating rate of 0.1 to 500 K.min–1 under nitrogen atmosphere including modulated DSC. The glass transition temperature (Tg) are taken at the middle of the step transition in the second heating run. 2.4.7 Thermogravimetric Analysis (TGA) TGA analysis was performed on a TA (TGA Q5000 V6.1 Build 181) instrument. In this case small amount (10 mg) of sample was taken and heated gradually from 30 °C to 1000 °C at a heating rate of 10 °C/min under nitrogen atmosphere. 2.4.8 Scanning Electron Microscopy (SEM) Surface morphology of the polymers is investigated by scanning electron microscopy, SEM model: Supra 55VPO (ZEISS). All powder samples are directly sputtered with platinum to hinder electrostatic charge during the measurement. 2.4.9 Hardness In this method, a truncated cone is pressed by a spring in the specimen. As a measure of the hardness is the penetration depth, the SHORE hardness is defined as the difference between the numerical value 100 and divided by the scale value 0.025 mm in depth under the effect of the test force. 2.4.10 X- ray diffraction Wide angle X-ray scattering and small angle X- ray scattering of the poly (ionic liquid) and the ionic modified BIIR is studied with the help of X-ray diffraction. The objective of the study is to determine the interlayer distance (d- spacing) in the material. The Page 36


measurements are carried out in XRD 3003 (Seifert – FPM Freiberg / Sa) using Cu-Kα radiation (0.1542 nm wavelength) (monochromatisation by primary multilayer system) obtained with 40 Kv, 30Ma, measuring time of 30 seconds for each point. Calculation of Bragg values of d from the position of the scattering maxima (reflection) 2d sinθ = nλ d = Interlayer distance, θ = Scattering angle, n = order of diffraction, λ = wavelength of the radiation. 2.4.11 Electrical Measurement The electrical measurement was performed in Loresta GP MCP-T610 which is combined with ESP-Probe for the measurement of resistivity in 4 pin probe measurement method, where 4 needle-type electrodes are placed linearly on a sample, a certain current flows between 2 external pin probes (1 and 4), and a potential difference formed between 2 inner pin probes (2 and 3) is used to determine the resistivity. Specifications1. Measuring method - 4-pin probe, constant-current method 2. Measurement range [Ω] 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 3. Power supply - AC 85-264V / 47-63Hz / 92VA 4. 4-pin probe types - ESP

Page 37

Chapter 3: Synthesis and characterisation of reactive imidazole derivative

Chapter 3

Synthesis and characterisation of reactive imidazole derivative

Page 38


3.1. Introduction Ionic liquids are materials that are composed solely of cations and anions. The cations are pyridinium based, imidazolium based, phosphonium based, ammonium based IL. They have good solvating properties for a range of polar and non-polar compounds. Ionic Liquids have been considered as “green solvents” and are also known as “designer solvents” as their characteristics can be tailored by changing the cationic and anionic part. Depending on the length of the alkyl chain attached to the cationic moiety, the hydrophobicity and hydrophilicity of ILs can be tailored which increases with increasing length of the alkyl chain. Pyridinium based ILs are very novel compared to the imidazolium based ILs. Phosphonium based ILs is much more stable than imidazolium or pyridinium based ILs. Imidazolium based ILs attracted great attention because of their stability under oxidative and reductive conditions, humidity, their low viscosity, and their ease of synthesis. Imidazolium-based ILs has been used as catalysts for the improvement of reaction time, yield and chemo selectivity of many organic reactions.

3.2. Synthesis of reactive imidazole derivative starting with imidazole and dibromohexane 1. Imidazole (0.5gm, 0.00734 mole) is dissolved in dry tetrahydrofuran. Then it is stirred in inert nitrogen atmosphere at room temperature with sodium hydride (0.1762gm, 0.0073 mole) for 2 hours. 2. Then dibromohexane (1.79gm, 1.13 ml, 0.00734 mole) is injected to the reaction mixture. The reaction is continued for 20 hours. 3. Then after the completion of the reaction, the reaction mixture is poured into 100 ml of distilled water. 4. The organic layer is purified from the aqueous layer by repeatedly washing with dichloromethane (25ml) for at least 4 times. 5. The purified colourless viscous imidazole derivative is purified from rotatory evaporator and precipitated in diethyl ether.

Page 39


3.3. Results and discussion 3.3.1 1H NMR analysis The product obtained after reacting imidazole and dibromohexane in presence of sodium amide is characterised with 1H NMR analysis which shows that the imidazole is getting reacted on both the sides due to the same reactivity of the two bromine groups. And instead of getting the target monomer (shown in Figure 21), two other side products are also generated in high ratio which is shown in the 1H NMR spectra (Figure 20)

A

B

G

N

Br

N

C

A

D G B C D

G0

F E

Figure 20: 1H NMR spectra of imidazole reacted with dibromo hexane From Figure 20 it is observed that the resulting monomer is not the actually predicted monomer. Here the chemical shift value for the bromine terminating proton is δ=3.5ppm (A), it has a low intensity of nitrogen terminating end group arising at peak δ=6.8 to 7.2ppm (B,C) and along with that there are two peaks at δ=9.27-9.36ppm (E,F) and Page 40

Chapter 3: Synthesis and characterisation of reactive imidazole derivative 7.6ppm (D) arising because of the side products (protonated and both isde reacted imidazole compound). Peaks (G0,H) is for both side reacted imidazole. So this is not the targetted monomer. Imidazole with one side brominated hexyl chain and many others and this compound is found to be not stable at room temperature. It polymerises at room temperature. The target monomer is

N

Br N

Figure 21: Chemical structure of 1-(6-bromohexyl) imidazole. But instead of this, different oligomers are shown in Figure 22 E HN

Br N

and G0 Br

Br

N

N N

Br

G0

N

Br

Figure 22: Both side reacted side products.

3.3.2. Optimisation of the reaction condition to achieve the target monomer  

Adding sodium amide (NaNH2) in presence of triethylamine[N(C2H5)3] [N(C2H5)3] acts as a proton abstractor.

3.3.3. Synthesis of reactive Imidazole derivative [1-(6-chlorohexyl) imidazole] 1. Imidazole (2gm, 0.0294 mole) is dissolved in dry tetrahydrofuran. Then it is stirred in inert nitrogen atmosphere at room temperature with sodium amide (1.146gm, 0.0294 mole) for 2 hours. 2. Then 1-bromo-6-chlorohexane (5.85gm, 4.37 ml, 0.0294 mole) is injected to the reaction mixture. The reaction is continued for 20 hours under inert nitrogen atmosphere Page 41

Chapter 3: Synthesis and characterisation of reactive imidazole derivative 3. Then after the completion of the reaction, the reaction mixture is poured into 100 ml of distilled water. 4. The organic layer is purified from the aqueous layer by repeatedly washing with dichloromethane (25ml) for at least 4 times. 5. The purified colourless viscous imidazole derivative is purified from rotatory evaporator and precipitated in diethyl ether.

e

a N b

d N

Cl

d

e

c

c

a b

DMSO

Figure 23: 1H NMR spectrum of the target monomer Figure 23 shows the target peak at chemical shift values δ= 3.6ppm for chlorine terminating groups and δ=6.93 to 7.2ppm shows the nitrogen end to be free. So it was justified that it was not polymerised and this is the monomer we targeted. But here due to the presence of chlorine and bromine end groups in the reactant, the reactivity of the reactant is different and hence only the highly reactive group i.e. bromine end reacted with imidazole to give the targeted monomer. But here also along with the target monomer some protonated and both side reacted compound is also obtained at peak δ = Page 42

Chapter 3: Synthesis and characterisation of reactive imidazole derivative 9.3-9.4 and 7.7-7.8 ppm, these peak arises due to the presence of either ionic charge on Nitrogen atom or due to protonation. The monomer is -

N

N

Cl

Figure 24 [1-(6-chlorohexyl) imidazole]

The subsidiary oligomers formed in very minor ratio are:

Cl

N

N

Cl

and

HN

N

Cl

3.3.3.1 Purification of the mixture Thin Layer Chromatography (TLC) was performed in order to separate the pure compound from the mixture product. As a reference, in order to get the an idea of the retention factor of the target monomer, bromine excess product, imidazole, and the target monomer is analysed in TLC plate with silica S60 as a stationary phase and the mobile phase used is a mixture of ethyl acetate: hexane in the ratio 9.5:0.5.

Page 43


Figure 25: TLC chromatogram

With the eluent ethyl acetate: hexane in the ratio 9.5:0.5 the pure monomer [1-(6-chloro hexyl) imidazole] is separated from the mixture of product using column chromatography which is shown in Figure 26.

Figure 26: Column chromatography

Page 44


Procedure 1. A stationary bed of silica is prepared with hexane as a solvent. 2. Then a thin layer of sand is given in order to prevent the prevent the contamination of the stationary bed with the slurry (compound to be separated dissolved in minimum DCM and embedded with silica) 3. Then the slurry is packed along with a thin bed of sand on the top layer to protect the bed from direct solvent interaction. 4. Then the eluent is passed starting with the lowest polarity of the eluent (ethyl acetate: hexane = 10:90). 5. Then slowly the polarity is increased from 10% ethylacetate solution to 90% solution. 6. Parallely the separated solution is cross-checked in TLC plates to check the spots concerning the separation. 7. Then all the purified target monomer solution is collected at one place and evaporated the solvent and kept in vaccum for few hours. 8. Then the target imidazole derivative is obtained. 9. Then it is further checked with 1H NMR spectra.

3.3.3.2 1H NMR analysis From the NMR study (shown in Figure 27) it is observed clearly that the pure target monomer is separated out of the mixture product with the help of column chromatography. The purity of the target imidazole derivative is confirmed from the appearance of the peak at δ=6.98, 7.15 and 7.61 ppm. These three individual peaks arise due to the presence of three different protons (marked as A,B,C) in Figure 27.

Page 45


Figure 27: 1H NMR spectra of pure and impure monomer [1-(6-chlorohexyl) imidazole.

3.3.3.3. FTIR Analysis The appearance of the peak at 1673 cm-1 indicates the presence of the C=N and C=C bond which confirms the presence of imidazole. The peak at 3000 cm-1 shows the presence of methylene groups.

Figure 28: FTIR spectra of pure monomer [1-(6-chlorohexyl) imidazole] Page 46


3.3.3.4. Solubility Test: Table 1: Solubility of the reactants Reactant

Acetone

CHCl3

THF

Toluene

Acetonitrile

C2H5OH

H2O

CH2Cl2

Diethyle ther

Dibromohexane



















1-bromo6-chloro hexane



















Imidazoe



















CH2Cl2

H2O

Table 2: Solubility test of the products Result

C2H5OH

CHCl3

Hex 

1





2

S.S

S.S



3









Acetone

CH3OH

DMSO

THF













S.S







S.S





S.S









- insoluble

 - soluble S.S- sparingly soluble 1- Imidazole excess with dibromo-hexane at R.T 2- Bromine Excess with Imidazole at R.T 3- Organic part of 6-(1-chloro hexyl)-Imidazole at R.T

Page 47


3.3.3.5. Thermal properties 3.3.3.5.1. Differential scanning calorimetry (DSC) analysis

monomer

Figure 35: DSC graphical plot of pure monomer [1-(6-chlorohexyl) imidazole]

Conditions – Temperature range: -80 to 20 °C, heating rate: 10 °C /min, atmosphere: N2 It is observed from the DSC plot that the glass transition temperature of the monomer [1(6-chloro hexyl)-imidazole] is at around -56 °C.

Page 48


3.3.3.5.2. Thermogravimetric analysis

100

imidazole monomer

Weight (%)

80

60

40

20

0 0

100

200

300

400

500

600

700

800

900

Temperature (°C)

Figure 36. TGA plot of synthesised imidazole based reactive monomer From the Figure 36 it illustrates that the synthesised imidazole based monomer has high thermal stability up to 300 °C and hence it is can be applicable in high temperature reactions and modification of polymers.

Conclusion This synthesised monomer is highly reactive in nature due to the presence of the reactive chlorine end group. But for synthesising such type of reactive imidazole derivative 1bromo-6-chlorohexane has been a better choice of reactant with imidazole due to the different reactive sites present. Hence only bromie side end group reacts much faster than chlorine end group.

Page 49

Chapter 4: Synthesis of asymmetric polyionic liquid based on imidazole

Chapter 4 Synthesis of asymmetric polyionic liquid based on imidazole

Page 50


4.1. Introduction Due to rapid advances in the field of chemistry and physics, polyionic liquids (PILs) have attracted the materials scientists, as it is termed as potential “Green material” for future. It is a subclass of polyelectrolyte in which an ionic liquid (IL) species is present in each monomer repeating unit connected through a polymeric backbone to form a macromolecular. Ionic liquids (IL) are organic salts that are liquid at ambient temperature. ILs are composed of organic cations are based on alkylimidazolium, alkylpyridinium, alkyl ammonium and inorganic anions. There has been a great interest in using ionic liquids as solvents for chemical reactions in polymerisation and also in the modification of polymers.

4.2. Polymerisation of the monomer to form poly (ionic liquid) 1. The monomer (0.5gm) [1-(6-chlorhexyl)imidazole] is taken in a schlenk tube and bulk polymerization is performed at 120 C in presence of nitrogen atmosphere. 2. The reaction is performed at 30 minutes, 6hours and 24 hours, to get PILs of varying molecular weight. 3. Then the PILs are analyzed with NMR, MALDI, FTIR methods. 4. The surface and structure analysis is done in optical microscope and SAXS/WAXS study.

4.3. Results and discussion 4.3.1. 1H NMR analysis Figure 29 shows the 1H NMR spectra of the PILs where the polymerisation is done from 30 minutes PILs to 24 hrs. So with increase in time of the reaction condition there is a decrease of peak intensity at 3.53ppm, indicating the polymerisation of the end group (chlorine group in monomer) and there is increase in peak intensity at δ= 7.53ppm, 4.23ppm and 8.41ppm indicating methylene groups of the double side reacted imidazole forming imidazolium ring and more aromatic ring.

Page 51


Figure 29: 1H NMR spectra of Poly (ionic liquid)

4.3.2. FTIR Analysis:

Figure 30: FTIR spectra of poly (ionic liquid). From the FTIR analysis it is confirmed that there is a novel peak at 1690 cm-1 which is much broader than the peak in monomer, confirming the polymerization. The peak at 1450-1510 cm-1 is due to the stretching vibration of C-Cl bond. Page 52


4.3.3. Optical Microscopic image In order to study the surface morphology and the phases, the PIL is taken in between two slides and it is observed under optical microscope. The optical images are shown in Figure 31.

Figure 31: Optical microscopic image of PIL.

Hence it is clearly observed that there is a spherulitic structure formed (shown in Figure 31) which confirms the presence of crystalline phase and aqueous phase in the matrix.

Key point: In order to confirm the self-assembling behaviour due to the aggregation of ionic moieties, an experiment is done. This PIL is heated at a rate of 250 °C/ minute to obtain its melting point.

Page 53


The melting point of this PIL is 209 °C Then this molten PIL in kept at ambient temp for 24 hours and again optical microscopic image is taken after 48 hrs. The following images as shown in figure 32 are taken

cooled at room temperature

Molten PIL

After 24 hrs

After 48 hrs Figure 32: Optical microscopic image of molten PIL.

On cooling gradually, there is again the spherulitic growth starting along the edge of the melt. Hence it can be concluded that there is a reversible bond formation within the ionic groups.

Page 54


4.3.4. Morphological analysis For further satisfactory result with explanation, the morphology of the PILs are analyzed with SAXS and WAXS measurement (shown in Figure 33-34)

4.3.4.1. WAXS Analysis The morphological analysis of the PIL is done in WAXS and SAXS where it is observed that there is some crystalline region along with amorphous region. The sharp peaks at 2 theta value 21 and 24 shows that there is a crystalline phase as shown in Figure 33a,b.

Figure 33a: WAXS study of PIL. The crystalline phase content is 40% in the PIL which is estimated using a linear combination of Gaussian function and Lorentz function and the Bragg’s Equation – nλ= 2d Sinθ where λ= wavelength of the light used, d = spacing between the layers, Sin θ = Angle of incidence.

Page 55


Figure 33b WAXS study of PIL Peak fitting for WAXS curve with pseudo-Voigtian functions (linear combination of Gaussian and Lorentzian function) for each scattering maximum (crystalline reflections and amorphous halo) is shown above in Figure 33. So it can be concluded that there is a crystalline phase and an amorphous phase in it.

4.3.4.2. SAXS study:

Figure 34a: SAXS study of PIL

The appearance of maximum peak value in SAXS (d ~ 8.3 nm) could result from a (layered) morphology caused by the repeating behaviour of the chemical structure along

Page 56

Chapter 4: Synthesis of asymmetric polyionic liquid based on imidazole the polymer chain (intermolecular phase separation in between the ring segment and the hexyl segment, or from a layered crystalline/amorphous (lamellar) morphology.

Figure 34b: SAXS study of PIL

4.3.5. Thermal properties of the PIL The thermal analysis of the synthesized Reactive imidazole derivative [1-(6-chloro hexyl) imidazole] and the poly(ionic liquid) is shown below in Figure 36 – 37 which is observed through DSC and TGA anlaysis.

4.3.5.1. DSC study of the PIL: It is done at a temperature range of -100 °C to 150 °C to study the glass transition temp.

Page 57


1st heating

2nd heating 3rd heating

Polyionic liquid

Figure 36: DSC plot of PIL at 1st, 2nd and 3rd heating Here the glass transition temperature of the PIL is at around -66 °C. For the investigation of the thermal properties of the PIL, it was heated 2nd time. The 1st heating is performed up to 50 °C and the 2nd heating is done up to 150 °C. And in both the cases, the glass transition temperature is observed to be the same. The glass transition temperature is quite lower at ambient temperature.

4.3.5.2. TGA analysis Conditions:

Temperature range: RT (5min) to 800 °C; Heating rate:

10 °C /min;

Atmosphere: N2

From the TGA study it is observed that the monomer and PIL is stable up to about 300 °C and the residue at 800 °C is + 0.2%. The weight loss observed is within 5% which confirms the thermal stability of the monomer and poly(ionic liquid) as shown in the Figure 37. The high thermal stability of PIL is attributed due to the ionic clusters/micelle formation within the matrix and due to the long ionic chain formation there is existence of ionic interaction which attributes to high thermal stability.

Page 58


MR 1 – pure monomer MR 2 - PIL

Figure 37: Weight loss vs temperature study of PIL.

4.3.6. Electrical properties The electrical measurement was performed in Loresta GP MCP-T610 which is combined with ESP-Probe for the measurement of resistivity in 4 pin probe measurement method, where 4 needle-type electrodes are placed linearly on a sample, a certain current flows between 2 external pin probes (1 and 4), and a potential difference formed between 2 inner pin probes (2 and 3) is measured to determine the resistance.

Specifications – 1. Measuring method - 4-pin probe, constant-current method 2. Measurement range [Ω] 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 3. Power supply - AC 85-264V / 47-63Hz / 92VA 4. 4-pin probe types – ESP Volume resistivity (Ω.cm) = 1.423 × 10 7 Surface resistivity (Ω/cm2) = 2.656 × 10 7, The higher resistivity of the monomer and PIL leads to electrically insulating property. The presence of imidazolium ionic groups in the polymeric chain should have shown the electrically conducting property. But the insulating behaviour can be explained due to the Page 59

Chapter 4: Synthesis of asymmetric polyionic liquid based on imidazole non-availability of the ionic groups on the surface of the polymer. Here in PIL, the ionic groups are present within the chains surrounded by the hexyl segment which is non polar in nature preventing the free mobility of the ions results in anti-static behaviour.

Test for Exchange of groups at elevated temperature In order to test any exchange reaction takes place or not at elevated temperatures, a reaction is performed in which butyl imidazole is reacted with bromo butane at 80°C for 20 hours under inert nitrogen atmosphere. And after the separation of the product (1,3dibutyl imidazolium) it is characterised with 1H NMR shown in Figure 37a. C

N A

N

B

B

C

A

Figure 37a. Showing 1H NMR of butyl imidazole with bromobutane Here the peaks at δ= 7.69 and 7.81 ppm (marked as A,B) indicates that the reaction on both side of imidazole has taken place, resulting in dibutyl imidazolium compound.

Page 60

Chapter 4: Synthesis of asymmetric polyionic liquid based on imidazole Then in order to study the exchange reaction this product [dibutyl imidazolium] compound is further reacted with bromo octane at 80°C for 20 hours under inert nitrogen atmosphere and the resulting compound is analysed with 1H NMR as shown in Figure 37b. C

N A

N

A

B

C

B

Figure 37b. Showing 1H NMR spectra of reaction of butylimidazole with bromo octane Figure 37b illustrates that as there is no change in peak intensity and peak value, hence no exchange of the end groups has taken place at higher temperature.

Page 61


Conclusion Thus from this study of PILs it is confirmed that the PILs have high thermal stability and hence it is beneficial to use in case of high temperature reactions and applications. And it is clearly understood that this type of polyionic liquid does not undergo exchange of groups at high temperatures hence they are predicted to have well defined end and head groups.

Page 62

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber

Chapter 5 Utilisation of reactive imidazole derivative for modification of bromobutyl rubber

Page 63


5.1. Introduction There has been spectacular advancement in research in rubber chemistry and technology after the introduction of supramolecular chemistry in rubbers since the last decade. With the invention of a smart rubber system by Leibler et al [58-60], the concept of selfhealing elastomers came into existence. Leibler’s smart rubber is a polymeric material that is able to "heal" in the case of damage. Near room temperature, this process is reversible. This system is based on low molecular weight compounds that form a hydrogen bonded network. This supramolecular self-healing rubber can be processed, reused, and ultimately be recycled. The tear edges of a cut sample can be held together, and they will simply re-bond into apparent solidity. The reason for this is hydrogen bonding which are reformed in the interface between the compressed pieces. The smart rubber recovers its original mechanical strength within several hours after being split and subsequently recombined. Residual hydrogen bond donors and acceptors responsible for the self-healing properties of the elastomer remain unpaired until the newly exposed surfaces come in contact with each other, allowing formation of new intermolecular hydrogen bonds. As compared to conventional rubber, which is covalently cross-linked, it is assumed that a hydrogen bonded smart rubber system cannot continually hold mechanical stress without undergoing gradual plastic deformation, and strain recovery is typically low [61-63]. This limits potential applications significantly. To overcome this problem, a self-healing rubber system is required that fulfils the mechanical performance of conventional rubber without to lose its long term dimensional stability. In such a rubber system, the ratio of permanent and reversible bonds should be well balanced. Permanent covalent bonds are assumed to contribute more to the mechanical performance of the material, whereas hydrogen bonds or ionic interactions may be responsible for its self-healing behaviour. The reversible and dynamic nature of hydrogen and ionic interactions are assumed to induce self-healing processes in the case of material damage.

Page 64

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber This innovative concept of self-healing has already been applied on well-established bromo-butyl rubber (BIIR) [64,65]. This elastomer possesses reactive allylic bromine groups which are susceptible to nucleophilic substitution [66-68]. Modification of BIIR with butyl imidazole has already been described [69]. In this modification, imidazolium ions are formed which tend to form ionic clusters. This ionically modified BIIR behaves like a conventionally sulphur cross-linked rubber which, additionally, shows pronounced self-healing [71-73]. The reason for the self-healing behaviour observed are the ionic interactions which are strong at ambient temperature and diminish at higher temperature. The dynamic reversible nature of the ionic interactions is responsible for the self-healing behaviour observed. But, the conversion of BIIR with butyl imidazole has some drawbacks. It only allows introducing of small amounts of ionic groups since BIIR possesses only a small percentage of reactive bromine groups. In order to overcome this problem, it is intended to utilise a reactive imidazole derivative which will be able to form longer sequences of a polyionic liquid grafted to the BIIR backbone. This approach allows introducing a larger number of ionic groups per bromine group in BIIR without to cross-linking the rubber covalently. It is assumed that such an approach may help to improve the self-healing behaviour.

5.2. Methods of ionically modified BIIR 5.2.1. Modification of bromo-butyl rubber with the reactive imidazole derivative [1-(6-chloro hexyl)-imidazole] The modification of BIIR was performed at various conditions (varying temperature and time) and in various ways with the varying proportion of the monomer [1-(6-chloro hexyl)-imidazole]. Special care is taken to find an optimum ratio of the percentage of grafting of the monomer with active brominated site of BIIR and also the polymeric ionic chain formed during curing.

Page 65

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber The following methods are used for the optimizing a suitable condition for the modification of BIIR that are as follows:

5.2.1.1. Solid state BIIR reaction with [1-(6-chloro hexyl)-imidazole] BIIR (57gm, 0.0081moles of active bromine content) was pre-mixed at a temperature of 25 °C, 35 °C and 45 °C in HAAKE Rheomix OS, Rheo Drive 7 with banbury rotor R600 rotating at a speed of 501/minute for 5 minutes and then the monomer [1-(6-chloro hexyl)-imidazole] was added and the mixing was done for 15 minutes. The operating temperature was varied from 25 °C, 35 °C and 45 °C. Then an optimum condition was investigated for the proper dispersion of the reactive imidazole derivative throughout the matrix of BIIR. Special care was taken not to have any crosslinking or polymerization at the time of dispersion. Then the compounded elastomer was investigated for its rheological study and 1H NMR study to measure the percentage of grafting of the ionomer onto the active allylic brominated site at the time of curing.

5.2.1.2. Solution based mixing: In this method the BIIR (57gm, 0.0081moles of active bromine content) was solubilised in tetrahydrofuran (THF) at room temp for 24 hrs and then the reactive imidazole derivative was added and then the reaction was stirred with a magnetic stirrer for 24 hrs at a room temperature. Then this compound was investigated with 1H NMR analysis to study the percentage conversion of the grafting and its rheological property was also investigated

5.2.1.3. In-situ generation of reactive imidazole derivative in solid state reaction with BIIR BIIR ((57gm, 0.0081mole of active bromine content) was pre-mixed at a temperature of 25 °C, 35 °C and 45 °C for 5 minutes in HAAKE Rheomix OS, Rheo Drive 7 with banbury rotor R600 rotating at a speed of 501/minute. The operating temperature was varied from 25 °C, 35 °C and 45 °C. Then in order to generate the reactive imidazole monomer in-situ, all the reactants were added simultaneously and the mixing was continued for 15 minutes. Then the compounded elastomer was taken for the investigation of its rheological properties and 1H NMR study. Page 66


5.2.1.4. Solution based in-situ generation of reactive imidazole derivative with BIIR BIIR (57gm, 0.0081moles of active bromine content) was dissolved in tetrahydrofuran for 24 hrs at room temperature and then the reaction temperature was performed at 60 °C. Then imidazole (0.7 gm, 0.0102 mole), 1-bromo-6-chloro hexane (1.5ml, 0.0102 mole), sodium amide (0.39 gm, 0.01 mole) and triethyl amine (1.01 ml, 0.0102 mole) are mixed with magnetic stirrer for 24 hrs and then the molten compound was casted into thin films. Then it was kept immersed in chloroform for 20 hrs for the removal of unreacted reactants and then it was investigated for characterization.

5.2.1.5. Solid state mixing of BIIR with imidazole BIIR (57gm, 0.0081mole of active bromine content) was also mixed with imidazole (0.55gm, 0.00808 mole) in HAAKE Rheomix OS, Rheo Drive 7 with banbury rotor R600 for 15 minutes after being pre-mixed for 5 minutes at 35 °C and then its rheological properties were studied with further characterisations.

5.2.1.6. Solid state mixing of BIIR with sodium amide BIIR (57gm, 0.0081mole of active bromine content) was mixed with sodium amide (0.32gm, 0.0081 mole) using the same pathway as stated above for imidazole. Then this compounded elastomer was investigated for further characterisation.

5.3. Results and discussion In order to realize that there is a formation of non-covalent bonding in the blend of bromobutyl rubber and poly (ionic liquid), the possibility of formation covalent bonds through crosslinking is avoided. The formation of such non-covalent interaction may be only possible if there is complete grafting of the reactive imidazole derivative [1-(6chloro hexyl)-imidazole] to the active allylic brominated site.

Page 67

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber So in order to achieve a higher percentage of conversion to produce ionically functionalized BIIR several attempts are taken to optimise the reaction condition (temperature, time) in which the mixing and dispersion of the reactive imidazole monomer should take place. So to carry out this work, BIIR (57gm) is cut into small pieces and put into the HAAKE internal mixer, then the BIIR is pre-mixed for 5 minutes at several temperatures (25°C, 35°C and 45°C), then the reactive imidazole derivative (synthesized monomer) [1-(6-chloro hexyl)-imidazole] is added to the reaction mixture and the mixing is done for 15 minutes. Though, theoretically it may be possible to have 100% conversion. But, several suitable conditions were investigated to attain the maximum conversion. The mixing is performed at 45 °C first, while the mixing torque was recorded which is significantly higher indicating the viscosity of the mixture to increase. This increase in torque may be due to the ionic interaction within the chains which was restricting the mobility of the chains. Hence curing is taking place at the time of mixing or dispersion of reactive monomer. Then it was investigated for the percent conversion in 1H NMR analysis where the percent conversion and the rest of the monomer getting polymerized is investigated which is forming poly(ionic liquid) chains within the matrix. Due to which there is an ionic network formed which is responsible for the increase in torque. So with this concept we moved forward to work on finding suitable mixing conditions where the percent conversion will increase further and we can estimate the ratio of percentage grafted to the active brominated site with the percentage of polymerized ionic group. So in order to avoid the premature curing the mixing is performed at 25 °C where it is observed that the torque is not rising but the reactive monomer is not at all properly dispersed into the BIIR matrix. So again the same experiment is performed at 35 °C with varying amount of reactive imidazole monomer (50 mole%, 100 mole%, 200 mole%) and it is observed that the torque is under control with proper dispersion of the reactive monomer into the BIIR matrix. The mixing was performed for 15 minutes. The characterisation of butyl rubber by 1H NMR spectroscopy (shown in Figure 39) has been described in the literature where it is illustrated that the exo-methylene bond is more reactive than endo form.

Page 68

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber Diagram of exo BIIR

Exommethylene isomer n

Br

m

Figure 38: Exo isomer of BIIR As bromo-butyl rubber contains around 1.5 – 2% of isoprene units in which only 2.5 wt % of active brominated isoprene unit is present. So the grafting site within BIIR is very less.

Figure 39: 1H NMR spectra of exo-BIIR.

The modification of bromo butyl rubber is done by grafting the synthesised asymmetric imidazole derivative [1-(6-chloro hexyl) imidazole] at the allylic site of BIIR. The grafting is performed at various temperatures in order to increase the percentage Page 69

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber conversion which is observed with 1H NMR spectra which is shown in figure 40. The appearance of the peak at δ=4.96ppm illustrates that the methylene proton when imidazole derivative is attached at allylic bromine site. Hence on increase in grafting percentage there will be decrease of peak intensity at δ=5.03 and 5.41ppm (shown in Figure: 40

Figure 40: 1H NMR spectra of pure BIIR and ionic modified BIIR subsequently. While grafting of this imidazole derivative it is assumed that there will be a formation of polymerised ionic chain along with grafting which will increase the number of ionic groups and help in development of mechanical properties and self-healing property even at lower percentage of conversion (grafting of reactive imidazole derivative onto BIIR). The schematic diagram is shown in Scheme 6.

Page 70

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber Schematic diagram of ionic groups in pendant position

Br

Br N

Cl N

N

N N

N

Scheme 6: ionic liquid-g-BIIR. The rheometric curves of mixing done at 45 °C at various temperatures is shown in Figure 41 MR1@80 MR1@100 MR1@120 MR1@140 MR1@160

3.5 3.0

Torque(dN.m)

2.5 2.0 1.5 1.0 0.5 0.0 -0.5 0

10

20

30

40

50

60

Time(minute)

Figure 41: Rheograph of ionic modified BIIR (1st mixing done @ 45 °C). Hence it is observed from figure 41 that on moving from 80 °C to 100 °C there is an increasing torque which means there is a marching curve which shows increase in

Page 71

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber molecular weight and viscosity also increases. Furthermore the torque falls with increasing the temperature from 120 °C to 140 °C again. Hence it can be concluded that at higher temperature the ionic interactions forming a physical network are not stable, hence they get destroyed/dissolved at higher temperature. So as the maximum torque is achieved at 120 °C hence it is assumed that at 120 °C there will be maximum interaction which will lead to improved properties. Then these samples are investigated for 1H- NMR analysis (shown in Figure 42-43) where it is observed that there is only 18% conversion taken place at 140°C, and the rest of the monomer is assumed to have polymerized at that high temperature while doing compression moulding. C5H10Cl

A H2C N

H H

B

N

C

C

Br

H

A B

Figure 42: 1H NMR spectra of ionic modified BIIR at 140 °C (1st mixing @ 45°C).

Page 72


Figure 43: 1H NMR spectra of ionic modified BIIR at 100 °C (1st mixing @ 45°C). 1

H NMR spectra in Figure 42, the characteristic resonance at δ = 5.41 ppm and 5.04ppm

signifies the presence of allylic proton and its high intensity concludes the lower isomerisation of the bromine group to the allylic position. And the intensity of this peak is higher at 100°C than 140°C signifying lesser isomerisation of bromine group at 100°C. The peak at δ = 4.06 ppm signifies the unreacted allylic bromine group. The important peak at δ = 4.96 ppm is due to the substitution of the allylic bromine with reactive imidazole derivative. And it is observed that the intensity of the peak at δ = 4.96ppm is higher at 140°C rather than 100°C. The peak at δ = 4.35ppm signifies the unreacted monomer [1-(6-chlorohexyl)imidazole]. Hence it can be observed that the grafting of the reactive monomer [1-(6-chlorohexyl) imidazole] is not achieved at maximum extent. So to further increase the percentage of grafting/conversion, the mixing temperature is optimised at 35 °C where it is expected to properly disperse the reactive imidazole derivative (synthesised monomer). So after the optimum reaction temperature is found. The samples are studied with rheometer to estimate the curing behaviour and curing time by varying the temperature from 100 °C to 140 °C. Then with the estimation of the T90 = time for 90% conversion of the mixture into cured elastomer, it is cured for specific time. As synthesised monomer [1-(6-cloro hexyl) imidazole] is having high thermal stability so curing can be done at high temperature.

Page 73

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber The proportion of the isoprene content in BIIR is 1.5-2% out of which only 64% are brominated. Theoretically 100% conversion of the brominated allylic sites in BIIR can be possible but here it is observed at 120 °C there is only 18% conversion and at 140 °C it is little higher. So the reason behind the difference in practical conversion and the theoretical conversion is predicted to be due to the liberation of HBr during the isomerisation of alkylation reaction. Hence it reduces the amount of allylic bromine groups, which was responsible for the reaction to take place. 0.75@100 1.5@100 3@100

3.5 3.0 2.5

Torque (dN.m)

2.0 1.5 1.0 0.5 0.0 0

10

20

30

40

50

60

Time (minutes)

Figure 44: Rheograph of ionically modified BIIR @ 100 °C (2nd mixing @ 35°C).

Page 74


0.75gm@140 1.5gm@140 3gm@140

2.5

2.0

Torque (dN.m)

1.5

1.0

0.5

0.0 0

10

20

30

40

50

60

Time (minutes)

Figure 45: Rheograph of ionically modified BIIR @ 140 °C (2nd mixing @ 35°C). For the mixture at 35 °C, the percent conversion is estimated to be 25% which is maximum obtained with respect to grafting practically. So the rest of the monomer [1-(6chlorohexyl) imidazole] has polymerised forming polyionic chains that formed a physical network. But for the samples where mixing is carried out in solution based reaction, in-situ generation of the reactive imidazole derivation in reaction mixture with BIIR and also in other mixing are analysed in rheometer to study the curing behaviour where it shows higher torque. So it is found interesting to investigate the samples. But when it is taken for 1H NMR analysis then the samples are not soluble in CDCl3 (deuteriated chloroform). Hence it is concluded that those samples are cross linked. So as we are looking into the formation of non-covalent bonding these samples are not purposeful for our investigation. But in order to investigate the reason behind cross linking at such condition (solution based, in-situ generation of reactive imidazole derivative in solution as well as in internal mixer) these samples were investigated for mechanical and rheological properties and it was assumed that it may be due to the cross linking of BIIR with imidazole and sodium Page 75

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber amide at high temperature generated due to the shear. Hence, the ionic-g-BIIR is given for the investigation of its mechanical property, electrical property, thermal property and self-healing property.

5.4. Characterisation of modified BIIR All the compositions (mixed at 45 °C and 35 °C at speed 501/minutes for 15 minutes) are analyzed for the thermal properties in DSC and TGA instruments. And sample specimens are cut for the investigation of the mechanical properties. Among all these conditions, the mixing done at 25 °C resulted in a poor dispersion with very sticky BIIR after curing, in other words it is behaving as like an uncured raw BIIR. Hence, this sample is not taken for further investigation. But the other moulded ionic modified BIIR is taken for further investigations of its thermal, electrical, and mechanical properties.

The following table 3 shows the conditions I which mixing of BIIR + Reactive imidazole derivative (monomer) has taken place:

Temp of

Moulding

mixing (°C)

temp(°C)

A

25 °C

140 °C

15

Amount of derivative [1-(6-chloro hexyl)imidazole] 0.75gm

B

45 °C

100 °C

50

2.2gm

C

45 °C

100 °C

50

2.4gm

D

35 °C

140 °C

30

0.75gm

E

35 °C

140 °C

30

1.5gm

F

35 °C

140 °C

30

3gm

G

35 °C

140 °C

10(100°C)+10(120°C)+10(140°C)

1.5gm

Specimen

Moulding time (minutes)

Page 76


5.5. Thermal Analysis 5.5.1. Thermo gravimetric analysis (TGA) While performing this experiment, the sample (9mg) is heated from room temperature (5minutes) up to 800 °C at a heating rate of 10K/min in inert nitrogen atmosphere. After 800 °C heating there is only 0.7% residue left and the decomposition temperature of the compound is found at around 300 °C, which confirms its high thermal stability. The reason is due to the ionic cluster formation leading to ionic interaction within the layers/chains. The weight loss even at final temperature (800 °C) is found to be within the range of 5% which is shown in the following graphical plot as shown in Figure 46.

Figure 46: Thermo gravimetric analysis of the ionic modified BIIR

Page 77


5.5.2. Differential Scanning Calorimeter (DSC) Analysis In this method of study the different types of phase transition. The compound (5.5 gm) is heated in two stages. The 1st heating is performed from -80 °C to 50 °C and the 2nd heating was done from -80 °C to 150 °C at a heating rate of 10 °C /min. And the glass transition temperature is found to be at around – 64 °C in both the stages which is clearly shown from the given Figure 47. The reason behind it can be explained that such type of ionic clusters leads to some plasticisation effect, thereby lowering the Tg. Hence such ionic modified BIIR may contribute towards low temperature applications. Due to the formation of the ionic cluster, it is predicted to have a melting point of the ionic clusters at higher temperature above 120°C, which is confirmed from the DSC analysis.

MR1 – 0.75gm CHI+BIIR MR2 – 1.5gm CHI+BIIR MR3 – 3 gm CHI+BIIR

Tm = 120 °C of ionic cluster

Tg = – 64 °C of ionic modified BIIR

Figure 47: Thermal analysis of ionic modified BIIR

Page 78


5.6. Mechanical Properties 5.6.1. Dynamic Mechanical Analysis 1.5gmCHI+BIIR Pure BIIR s-BIIR

10000

1200

9000 1000

8000 7000

800

5000

600

4000 400

3000 2000

E''(MPa)

E'(MPa)

6000

200

1000 0

0

-1000 -60

-40

-20

0

20

40

Temperature (°C)

Figure 48: Dynamic mechanical analysis of ionic modified BIIR (mixing @ 35 °C).

From the graphical plot of modulus versus temperature it is clearly stated that the modulus behaviour is quite similar for physical crosslinked BIIR and sulphur covalent crosslinked BIIR. Physically crosslinked BIIR has nearly the same stiffness as the sulphur cross linked BIIR. Here the storage modulus of the ionic modified BIIR is nearly the same as sulphur covalent crosslinked BIIR. In case of loss modulus, at lower temperature range the loss modulus was higher for ionic modified BIIR but after -55 °C the sulphur covalent cross linked BIIR dominants.

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5.6.2. Tan δ vs Temp 1.5gm(100mole%) pure BIIR s-BIIR

1.6 1.4 1.2

tan d

1.0 0.8 0.6 0.4 0.2 0.0 -100

-50

0

50

100

150

200

Tempearture(°C)

Here from the plot of Tan δ vs temperature curve (shown in Figure 49), typical wide glass transition range for the BIIR is observed. The shoulder at about -50 °C is probably due to a low temperature process or presence of branches in BIIR or due to the bromine groups. At higher temperatures, it is seen that the curve of the mixtures remains stable in comparison to pure BIIR that starts to flow. This may indicate that the modified BIIR behave like elastomer (covalently crosslink sulphur BIIR), and not like uncured rubber upto a certain temperature but fails at above 120°C due to the dissolution of ionic clusters. Here one may expect to have another hump in the higher temperature region due to the ionic cluster formation but it depends upon the amount and nature of the ionic cluster formed. But it is good to see that the mechanical property of such modified BIIR is like covalent crosslink rubber but at higher temperature it shows the viscous flow which is an indication that it is not covalently cured. Hence there is no negative impact of the additives on BIIR.

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5.6.3. Stress-Strain Curve From the study of the stress-strain relationship it can be clearly stated that with increase in the ionic content in the modification of BIIR the elongation increase. The elongation (%) is much better in ionically modified BIIR than sulphur covalent cross linked BIIR (shown in figure 50) which may be explained due to the long side chains arranged by the stretching laminar and slide on one another, thus enabling a higher elongation. Hence the ionic modification of BIIR has proved to have better stress-strain property than covalent cross linked BIIR.

Figure 50: Stress- strain behaviour of ionically modified BIIR @ 100 °C. Hence, the ionic modified BIIR has proved to have better mechanical property than covalent cross linked rubber up to certain higher temperature before which the ionic clusters does not degrade. The higher elongation may be attributed because of the ionic interaction when one layer chain of BIIR is slipped over the other at the time of

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Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber stretching. Hence the elongation is higher when the amount of ionomer is higher, which can be explained due to the strong ionic interaction among the chains. It can be explained also because of the ionic groups present in the pendant position of the BIIR chains there is enough space for the modified chains to stretch, resulting in higher elongation.

5.6.4. Hardness data table Specimen

Hardness (SHORE A)

A (2.2gm CHI+BIIR)

27.8

B (2.4gm + BIIR)

27.9

C (0.75gm +BIIR)

25.3

D (1.5gm + BIIR)

25.6

E (3.0gm + BIIR)

28.8

This data illustrates that on increasing the ionic content of the modified BIIR the hardness increases substantially.

5.6.5. Surface morphology and phase morphological analysis (SAXS / WAXS) study This study of surface morphology and phase morphology is studied through X-ray diffract metric analysis which is shown in figure 51-52. The reason behind the improvement in mechanical properties without being covalently cross linking is proposed due to the formation of ionic non-covalent interactions among the chains when BIIR is modified with ionic group. Hence such ionic interactions may form some small ionic clusters with the matrix which is believed to be responsible for any self-healing characteristics. Hence, it is predicted that due to the formation of the ionic clusters within the BIIR matrix, there would be a phase difference which could be predicted from the SAXS and WAXS study.

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5.6.5.1. WAXS study of ionic modified BIIR Figure 51 clearly illustrates that there is a crystalline phase along with the amorphous phase and hence, there is the appearance of the sharp peak with a broad hump. Hence, it is concluded that there is presence of ionic clusters within the BIIR chains arising due to the ionic interactions which s observed in the form of sharp peaks (small intensity) as the amount of ionic groups used in the modification is very less.

Figure 51: WAXS analysis of ionic modified BIIR.

5.6.5.2. SAXS study of ionic modified BIIR From the results of SAXS and WAXS, it can be clearly stated that there is a sharp peak arising at d = 4.9 nm which indicates the presence of the layered structure arising from laterally arranged side chains. It is then predicted that the side chains are forming comblike structures and there is a liquid- crystalline phase. But as the amount of ionic groups (50mole%, 100mole%, 200mole%) in BIIR is in very small amount as compared to the amount of BIIR (57g) hence the estimation of the crystalline phase is not possible in this measurement. But it is clear from the SAXS and WAXS spectra that there is a formation

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Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber of non-covalent bond i.e. the ionic interaction within the modified BIIR which is predicted to form reversible dynamic bond.

Figure 52: SAXS analysis of ionic modified BIIR 100 °C. Hence there is an indication of non-covalent bond formation which is reversible in nature lead to the idea of self-healing characteristic in the ionic modified BIIR.

5.7. Self healing Mechanism This self-healing mechanism in this ionic modified BIIR is due to the ionic interactions with the two surfaces when the two surfaces are brought close to each other with a slight finger pressure kept at ambient conditions. The concept behind the self healing mechanism of ionic modified BIIR is shown in Scheme 7.

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Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber The proposed mechanistic pathway is as follows

Ionic modified BIIR

Cracks and failures due to application

Rearrangement of ionic clusters – Healing of cracks

Scheme 7: Self-healing mechanism of ionic modified BIIR.

The self-healing mechanism is carried out in the following pathway –

Scheme 8: Healing mechanism due to ionic interactions.

5.7.1. Test for self-healing In order to observe the self-healing behaviour of the ionic modified BIIR, the dumbbell shaped tensile sample specimens are cut from the middle with scissor and then the cut pieces are brought together with finger at room temperature and then they are kept at the following conditions (shown in Table 4) to examine its self-healing behaviour.

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Table 4 Conditions for showing self healing behaviour Specimen

Duration

Temperature condition

A (50 mole %)

24hrs

RT (1st 10 min at 140 °C)

B (100 mole %)

24hrs


C (200 mole %)

24hrs


After the optimum condition the self-healed cut specimens are taken for the tensile testing under the same condition as the uncut specimens.

5.7.2. Stress- strain curve for the self-healed specimen 50mol% 200mol% 100mol%

0.50 0.45 0.40

stress (MPa)

0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0

50

100

150

200

250

300

350

400

strain (%)

Figure 53: Stress-strain behaviour of self-healed specimen. With the curing of the specimens at room temperature (1st 10 minutes @ 140 °C and then kept it for 24 hrs) the specimens are showing a stretching of up to 400% elongation. Hence it can be positively emphasized that the cured samples may be stretched considerably more during thermal treatment. This indicates faster healing. This could be Page 86

Chapter 5: Utilisation of reactive imidazole derivative for modification of bromobutyl rubber due to the fact that the ion clusters can move and it may be also explained because of the poly ionic chain formation there will be an ionic interaction at each point during slippage of one chain over the other and rearrange better at higher temperatures and thus quickly find at the interface of the crack.

5.8. Microscopic investigations The optical microscopic images (Figure 54) and the SEM images (Figure 55) show the surface of a cured sample after a healing period of 24 hours at room temperature, the two sides of the cut are penetrated and the plain of cut is well closed. The small cracks on the surface are due to sample preparation and electron irradiation. The optical images were also taken after 16 hrs which confirms the healing of the cut surface after keeping the samples at optimum condition (10min @140 °C + 16hrs).

0.75gm CHI +BIIR

1.5gm CHI + BIIR

3gm CHI + BIIR Figure 54: Optical images of self-healing surface of ionic modified BIIR after 16 hrs at Room Page 87

temperature. (The images were taken at different magnifications of 10 microns).


5.9. Electron microscopic images The cured samples were cut perpendicularly by a razor blade and joined together again. The samples were kept at 140 oC for 10 minutes and cooled at room temperature slowly. They were kept at room temperatures for 24 hours to self-heal the cutting surfaces. Afterwards the samples were investigated by scanning electron microscopy. The samples were sputtered with 3 nm of platinum to charging and to improve the image quality. From the SEM images (Figure 55 a and b) it can be clearly seen that the cutting surfaces were healed by intermixing of ionic liquid from both sides, thereby restoring the ionic clusters at the junctions. This restoration of ionic clusters are due to the strong oppositely charged ionic interactions of the chains of ionic liquids. A closer view of the cutting junction at higher magnification shows hardly any cutting surface after 24 hours. These clearly deonstrate a very high efficiency of self healing charateristics of ionically modified bromobutyl rubber. 1

Initially just after cut.

Figure 55: Representative SEM images of the healed ionic modified BIIR after 24 hrs at room temperature, keeping for 10minutes @ 140 °C at two different magnifications. Page 88


Conclusion Thus the modified BIIR with imidazole derivative shows non-covalent interaction due to the ionic cluster formation which shows better properties (mechanical, rheological and thermal) as compared to covalent sulphur crosslink. But this type of ionic cluster is not stable at higher temperature. They are stable almost up to 120°C where they show the same behaviour as covalently crosslink elastomer. But after 120°C they show flow behaviour which confirms the uncrosslink nature of the ionic modified BIIR. This type of modification leads to enhanced elongation at break which can be explained due to the ionic interaction within the poly(ionic) chain formed. When such modified BIIR is stretched with an applied stress there is some interaction with each consecutive ionic imidazolium sites resulting in enhanced elongation at break. Besides all these characteristics, there is another spectacular behaviour of this ionic modified BIIR which shows self healing behaviour at ambient temperature and condition. In this course of study it is investigated that even at a very minimum grafting percentage of ionic groups there is an improvement in the mechanical and self-healing behaviour which can be explained due to long poly(ionic) chain formation, which increases the number of ionic groups within the matrix. Hence this type of modification with reactive imidazole group proved to be beneficial.

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Chapter 6: Application of ionic liquid as solvent in RAFT polymerisation of butylmethacrylate

CHAPTER 6 Application of Ionic Liquid as a Solvent in RAFT Polymerisation of Butyl Methacrylate (BMA)

Page 91


Abstract This investigation reports the Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization of butyl methacrylate (BMA) in presence of imidazolium based ionic liquid (IL) as polymerization medium. In this case, the polymerization was quite faster in presence of IL named 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIHFP) compared to the conventional solvent like toluene. The polymerization was able to produce polymers with low dispersity as observed from GPC analysis. 1H NMR and MALDI-ToF analyses showed the presence of well defined RAFT end group in the polymer. Thermo Gravimetric Analysis (TGA) showed much increment in thermal stability for the PBMA prepared in presence of IL compared to toluene.

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6.1. Introduction Over many years lots of research work has been carried out in order to access a controlled radical method of polymerisation. Several methods are employed such as nitroxidemediated polymerisation (NMP) [1] atom transfer radical polymerisation (ATRP) [2] reversible addition-fragmentation chain-transfer polymerisation (RAFT) [3] and macromolecular design via the interchange of xanthates (MADIX) [4]. But within all, the comparative versatile method is using RAFT reagent as it controls better the method of polymerisation and can polymerise great variety of monomers such as styrene, acrylates, methacrylates, vinyl esters, polar or water-soluble monomers such as acrylamides and acrylic acid. The RAFT polymerisation was first discovered by researchers at CSIRO, reported in the late 1990s [5] In the RAFT process the CTA (charge transfer agent) is thiocarbonylthio function, and their structure can be schemed as Z-C(=S)-S-R where, Z is the activating group and R is the leaving or initiating group. In RAFT polymerisation the chain transfer agent (CTA) can be dithioesters (Z= alkyl or aryl), trithiocarbonates (Z= R'S-) and dithiocarbamates (Z= R'R''N-). Whereas, MADIX requires the use of xanthates i.e., dithiocarbonates (Z= R'O-) [6]. The diverse nature of RAFT reagents is due to variety of combinations of Z and R group. The activity of controlling the rate of polymerisation is governed by the different types of Z and R groups. Sometimes these RAFT reagents may get fragmented or disproportionate thereby acting as a macro RAFT agent which can further use in polymerisation [6]. In this investigation Butyl methacrylate (BMA) is polymerised using different RAFT reagents in presence of 2-butyl-2-methylimidazolium hexaphosphate (BMIHFP), ionic liquid (IL) as solvent. IL has been used as a solvent due to its very good suitable characteristics like high thermal stability, high boiling point, accelerates the rate of polymerisation, eco-friendly and non-toxic in nature [7]. Now-a-days IL is a very engulfing topics in the field of research due to rapid advances in the field of chemistry and physics. Poly ILs (PIL) has attracted the material scientists, as it is termed as potential “Green material” for future [8]. It is a subclass of polyelectrolyte in which an IL species are present in each monomer repeating unit connected through a polymeric Page 93


backbone to form a macromolecular chain [9]. Ionic liquids (IL) are organic salts that are liquid at ambient temperature. ILs are composed of organic cations are based on alkylimidazolium, alkylpyridinium, alkyl ammonium and inorganic anions [10]. There has been a great interest in using ionic liquids as solvents for chemical reactions and polymerisation reactions. They have wide range of glass transition temperature (Tg) [11]. PIL is used in modification of polymers leading to the development of new materials. There are various ways of preparing PILs i.e the chain growth polymerisation methods. In some cases vinyl monomers bearing imidazolium moiety is homopolymerised and copolymerised with vinyl comonomers based on styrene, (meth)acrylate and (meth)acrylamide etc via free radical polymerisation, controlled radical polymerisation (CRP), ionic polymerisation or via coordination polymerisations [12]. Till now lots of research works have been done using BMA with RAFT reagents in different solvent medium like toluene, xylene, 1,3 dioxane etc. But till now no work has been done in order to study the homo-polymerisation of BMA with RAFT reagents in presence of ionic liquid as solvent. The advantage of using BMA as monomer is that it can be used as a base material for coating and adhesive applications. It is used in resins, solvent, coatings, adhesives, oil additives, dental products, textile emulsions, leather and paper finishing due to its highly viscous, thermal stability and sticky nature of the polymer formed [13]. BMA is having the good properties like hardness, flexibility, clarity, colour compatibility, toughness, internal plasticisation and good weatherability. BMA is behaving like thermoplastic due to its glass transition temperature at 20°C, and having boiling point at 147°C, and its viscosity is slightly higher, hence the polymer obtained is viscous in nature [14]. In this investigation, it is very clearly reported the effect of ionic liquid on the rate of polymerisation of BMA with RAFT reagents and the separation of ionic liquid from its polymer. The compatibility of the different RAFT reagents with the BMA monomer was also studied. In this paper the effect of polymerisation in presence of ionic liquid, as solvent was also explored. Here, ionic liquid is not only enhancing the rate of polymerisation but also improves the property of the polymer formed. Page 94


6.2. RAFT polymerisation of BMA using ionic liquid Homopolymerisation of BMA was carried out in presence of ionic liquid (1-butyl-3methyimidazolium hexafluorophosphate) using different RAFT reagents. In a typic polymerisation reaction, BMA (0.25 g, 1.75 x 10-3 mol), CPDTC (0.0043 g, 1.24 x 10-5 mol) and IL (0.25 g, 8.79 x 10-4 mol) were taken in a Schlenk tube. The thermal initiator, AIBN (0.0005 g, 3.1028 × 10-6 mol) was added into the solution. Then the reaction mixture was heated at 90 °C under N2 atmosphere. The same reaction procedure was followed in case of RAFT reagent CPBDT. The schematic diagram of the RAFT polymerisation of butylmethacrylate is shown in Scheme 1.

R

S

S C

Butylmethacrylate

R

Z

AIBN

S

S C

Z

Scheme 1. Method of RAFT polymerisation

6.3. Results and Discussion BMA was polymerised via RAFT polymerisation in IL using different RAFT reagents at 90 °C (Scheme 1). Fig 1 shows the kinetic plot of the RAFT polymerisation of BMA in presence of IL using CPDTC and CPBDT RAFT reagents. The linear kinetic data shows that the polymerisation was controlled during polymerisation. In case of quick chain transfer to the RAFT agent, AIBN acts as a quick producer of initiators for propagating Page 95


radicals. The AIBN initiated system has lower rate of conversion at 70 °C as compared to the same at 90 °C. The rate of polymerisation increases as the ratio of the monomer: initiator is decreased as because higher the amount of the initiator, higher is number of propagating units, but the polymerisation may not be controlled enough. There will be a broad molecular weight distribution due to formation of many side products forming tendency. Here the ratio of monomer: RAFT: initiator used is 1:1:0.25. During propagation the concentration of the active radical is effectively controlled by the reversible chain transfer that is in equilibrium with the chain equilibration induced by the CPDTC or CPBDT RAFT agent. The polymer formed is having low molecular weight distribution value indicates that the polymerisation is controlled. GPC analysis shows the lower dispersity of molecular weight. The % of conversion of the polymer with respect to time is investigated by GC instrument which gives more or less linear plot showing the rate of polymerisation is controlled. RAFT polymerisation of BMA using various RAFT reagents in IL is shown in Table 1. The above polymerisation is done in bulk and also in toluene as solvent. CPDTC is having better solubility in toluene due to its long alkyl chain. CPBDT shows faster rate of polymerisation as compared to CPDTC. The PDI value is also very less in case of CPBDT as compared to CPDTC. The temperature 90°C was found to be optimum polymerisation temperature in terms of monomer conversion and controlling the molecular weight and lower Ð values. When the RAFT polymerisation was carried out at 70 °C, the polymer showed high Ð value and also the conversion was less. The polymerisation was very slow and high Ð value in case of CTBPA as RAFT reagent.

Page 96


Page 97


4. Chain Equilibrium/ Propagation: CH3 H3C

C

CH3 H2 C

CN

S

C

C C

O

O

C4H9

S

Pn

Z

CH3 H3C

Pn

Pm

S

S C

CH3 H2 C

CN

S

C

S

C

O

O

Z C4H9

Pn

C

Z

Pm

where, Z = SC12H25 or SC6H5

Scheme 2: Mechanism of RAFT polymerisation of BMA.

Here, the Z group is C12H25 in case of the RAFT reagent CPDTC (2-cyana-2propyl dodecyl trithiocarbonate) and Z = C6H5 in case of the RAFT reagent CPBDT (2-cyano-2propyl-benzodithioate).

6.3.1. Polymerisation Kinetics The kinetic study of the homopolymerisation of BMA in IL is analysed and from the given graph it is concluded that the rate of polymerisation is more or less controlled throughout the polymerisation. The per cent conversion of the polymer is also calculated using the following formula: Conversion (%) = (Peak area of reaction mixture)t0 – (Peak area of reaction mixture)tt (Peak area of reaction mixture)t0

Page 98


20 2 R = 0.99706

CPDTC CPBDT

ln 1/(1-x)

15

Kapp = 2.04 x 10

-1

10

2 R = 0.99554

5

Kapp = 3.54 x 10

-2

0 0

20

40

60

80

100

Time (min)

Figure 1: Polymerization Kinetics of the RAFT polymerization of BMA in presence of IL.

In case of CPBDT used as RAFT reagent the per cent conversion is maximum though in case of CPDTC as RAFT reagent the per cent conversion is marginally lesser than CPBDT. But the rate of polymerisation is more or less similarly controlled which can be observed from the given graphical representation of the two kinetic study graphs of the two RAFT reagent based polymerisation as given in Figure 1.

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Table 1: Homopolymerisation of BMA in presence of IL as solvent with RAFT reagents in various condition. Sl.

RAFT

Solvent

No.

Time

Temp

Mn,Theo

Mn,GPC

(h)

(°C)

(g/mole)

(g/mole)

Ð

Conv. (%)

1

CPBDT

Bulk

12

90

14,620

16,000

1.15

73.1

2

CPBDT

Toluene

11

90

14,260

19,000

1.18

71.3

3

CPBDT

IL

1:30

90

19,040

20,000

1.17

95.2

4

CPDTC

Bulk

12

90

16,480

26,000

1.39

82.4

5

CPDTC

Toluene

11

90

12,100

11,000

1.81

60.5

6

CPDTC

IL

2:00

90

18,740

11,000

1.22

93.7

[Monomer]/[RAFT]/[AIBN] = 560:4:1

6.3.2. 1H NMR analysis Fig. 2 shows the 1H-NMR data of PBMA prepared via RAFT polymerisation using IL as solvent. The disappearance of the resonances at δ = 6.4 ppm and 6.8 ppm for unsaturation (>C=CC=C< group concluded that the polymerisation has taken place. The peak appeared at 1150cm-1 for C-O group and at 3000cm-1 for the C-H stretching. As the reaction proceeds with time from 15 min to 2 h, there was gradual decrease in the intensity of the peak at 1680cm -1 indicating that the polymerisation has taken place. With increasing time the peak appeared at 1250cm-1 due to the C=S bond of RAFT group and the peak appeared at 1725 cm-1 for the C=O group in PBMA that is at pendant position. Page 101


90 min

%T (a.u.)

60 min

0 min

4000

3500

3000

2500

2000

1500

1000

500

-1 Wavenumber(cm )

Figure 3: FT-IR spectra obtained during the RAFT polymerisation of BMA in presence of IL.

6.3.4. MALDI-TOF-MS analysis It is a very good technique in order to establish the structure of the polymer with RAFT end group and also its molecular distribution. The polymer prepared via RAFT polymerisation having the end group moiety as Z group of the RAFT reagent (Z = -Ph, SC12H25) and at the other end of the polymer has the R group attached to it (R = CH3)2(CN)C-). MALDI-TOF-MS of BMA prepared in IL via RAFT polymerisation is shown in Figure 4. This analysis was carried out in positive ion reflectron mode using DHB as a matrix. Sodium trifluoroacetate was added as a salt to enhance the ionisation of polymer by cationization. The major peak arises at 1513, 1655.15, 1797.22, 1939.3 and 2080.41 (M/Z ratio) showing the consecutive peak difference of 142 which is the molar mass of BMA. Here In case of RAFT polymer of PBMA showed two types of molecular fragmentation during MALDI-TOF analysis. In one case, the weak C-S bond of the Page 102


RAFT end group was cleaved and there was no end group remains to act as a macroRAFT agent. The initiator R Group attached with both the ends of polymer chain. In another one type of fragmentation, there is one R Group attached at one end of polymer chain and on the other end there is no group attached. The calculation obeying distribution is as follows: e.g.1513.0080 (CH3)2(CN)C-(BMA)-HNa+ ( 142.20×10+23+68+1 = 1514 ). This indicates that the thioester moiety (–Z group) has been cleaved during the laser beam irradiation. Though soft laser is used in MALDI-TOF analysis but very weak –C–S is broken during analysis. The cleavage of thioester moiety (–Z group) in RAFT polymerisation during MALDI analysis has been reported by several authors. The initiating group (i.e. R group) remain unaffected during MALDI-TOF analysis. However, 1H NMR as well as FT-IR analysis showed that the presence of the desired RAFT end group attached with the polymer.

Figure 4: MALDI-TOF spectrum of PBMA. Page 103


6.3.5. TGA Analysis

CPBDT+ BMA+ Toluene CPDTC+BMA+ IL CPBDT+BMA+ IL

Weight Loss (%)

100

80

60

40

20

0 0

100

200

300

400

500

600

700

800

Temperature (oC) Figure 5: TGA thermogram of PBMA prepared via RAFT polymerization.

Figure 5 shows the TGA thermogram of the PBMA prepared by using toluene and IL as solvent respectively. In this case, the presence of IL as solvent increased the thermal stability of PBMA to higher extent in comparison with toluene.

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6.4. Conclusions From the above experimentation it can be concluded that ionic liquid is very helpful and useful in chemical reactions as it makes the reaction rate faster which can be proved from the above experimental results and the reactions are also controlled in presence of IL as a solvent.

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Chapter 7: Summary and conclusion

CHAPTER 7 Summary and Conclusion

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7.1. Summary and conclusion In this work, ionic liquid (1-Butyl-3-methylimidazolium hexafluorophosphate) is used in homo-polymerisation of butyl methacylate acting as a solvent. It has been shown in literature that ionic liquid acts as a better industrial solvent in chemical reactions, which has been proved in this study. In this project 3 different conditions are used – bulk polymerisation, solution based polymerisation (toluene as a solvent) and ionic liquid acting as a solvent. And in the study of the polymerisation reaction of butylmethacrylate with RAFT

reagents, 2 different RAFT reagents are used – 2-cyano-2-propyl

dithiocarobonate (CPDTC) and 2-cyano-2-propyl-benzodithioate (CPBDT). And within these two RAFT reagents, CPBDT is giving more controlled polymerisation with faster rate of polymerisation in presence of ionic liquid. Though the rate of polymerisation in ionic liquid acting as a solvent much faster than in bulk and in any other chemical solvent. And after the 1H NMR analysis and MALDI-TOF analysis it is confirmed that the rate of polymerisation is controlled and having a well defined end group with a faster rate of polymerisation. Hence this study proves again the utility and uniqueness of using ionic liquid as a chemical solvent in polymerisation. Moreover this type of ionic liquid when acting as a solvent is very easy to separate from the product and reuse it. So once again, ionic liquid has proved to be a beneficial and better solvent than other chemical solvent. Besides the application of ionic liquid as solvent in polymerisation it is also used in the modification of bromobutyl rubber. In this work bromo butyl rubber is mixed with reactive imidazole based derivative of polyionic fluids. At first BIIR is reacted with different amount of [1-(6-chlorohexyl) imidazole], to convert all possible reactive allylic bromine groups into imidazolium bromide group, and thereby preventing chemical covalent bonds. The reaction conditions are optimized by varying the mixing parameters and concentration of the reactive imidazole derivative [1-(6-chlorohexyl) imidazole]. Initially

Page 107


the premixing is done at 45 ° C. Specimens are obtained by pressing at temperatures around 100 ° C for 50 minutes. Under these conditions, a conversion of about 18% of the bromine groups is achieved and the rest of the reactive imidazole based monomer is converted into poly (ionic liquid). All ionically modified mixtures showed comparable and in some parameters improved thermal and mechanical properties than the conventionally prepared covalent cross linked mixture. Particularly noteworthy is the observation of self-assembling of the ionomers (polyionic liquid) which lead to the prediction of the self-healing behaviour in the ionically modified BIIR. Further tests on specimens cut-through showed that the ionic groups grafted onto the backbone of BIIR has the ability to heal an entire section to a certain extent and recover a specific part of the original mechanical properties. The results of the study reveal new phenomena whose causes are not clear at this time exactly. But in other words the predicted reason behind this self-healing behaviour is due to the self-assembling tendency of the ionic groups grafted onto BIIR, leading to the formation of small clusters which are not thermally stable at higher temperature, but it can be regained at ambient temperature. In particular, the crack propagation experiments by TFA require further attention. The difficulty in mixing with polyionic fluids could probably be avoided by addition of the reactive imidazole derivative little by little amount so that it gets well dispersed with BIIR and after grafting it will increase the polarity of BIIR to a very smaller extent but then addition of further reactive imidazole derivative will be much easily dispersed due to the better compatibility with the modified BIIR. The proportion of flexible aliphatic units could be varied. And it can be influenced by exchange of the anion and hydrophobicity of the ionic structure. The results of this study are promising and open new avenues for the development of self-healing elastomer based on known economically relevant elastomers and give rise to further investigation for a better understanding of self-healing effects. Even the scope of study for estimation of ratio between the grafting of the ionic groups onto BIIR with the Page 108


poly (ionic liquid) chain formed in-situ that increases the number of ionic groups into the matrix leading to better ionic interaction.

7.2 Future scope of work In this scope of study, a new method of ionic modification of BIIR has been investigated with satisfactory results. This method of modification will impart large number of ionic groups through formation of poly-ionic liquid chain besides grafting at the active allylic bromine site in BIIR which is very small in proportion. Hence, in near future, further studies could be possible focussing on the air impermeability behaviour and tear fatigue property of such modified BIIR as compared to pure BIIR. Our future aim is also to find the ratio between polymerised ionic liquid and the grafting (%) at the allylic bromine site in BIIR. Optimising the condition required for achieving highest possible grafting percentage onto BIIR allylic bromine site. And last but not the least, the mechanism and brief explanation behind such spectacular behaviour of ionic liquid will be a major field of study and research. In future I have few questions unanswered which I would like to investigate in near future – about how this ionic liquid is behaving as a better solvent, what is the mechanism with proper reason and explanation behind its unique property. I want to find a proper explanation behind the ionic liquid making the rate of polymerisation much faster. So I think the answers to these queries will prove beneficial in using ionic liquid as a commercial industrial solvent.

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Synthesis of ionic liquid and its application in rubber

Synthesis of ionic liquid and its application in rubber

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