Efficient chemical transformations of epoxidized

Polymer Degradation and Stability 140 (2017) 156e165

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Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab

Efficient chemical transformations of epoxidized soybean oil to crosslinked polymers by phosphorus-containing nucleophiles and study their thermal properties Chandra Sekhar Reddy Gangireddy, Yuan Hu* Fire Chemistry Section, State Key Laboratory of Fire Science, University of Science and Technology of China, Jinzhai Road 96, Hefei 230026, Anhui, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 22 February 2017 Received in revised form 25 April 2017 Accepted 29 April 2017 Available online 29 April 2017

In this study, biodegradable environmental friendly phosphorus containing oligomers were prepared from renewable resources by an efficient ring-opening polymerization of epoxidized soybean oil using tetrafluoroboric acid as a catalyst in most of the cases. The resulted oligomers were characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis and gel permeation chromatography. The results revealed that polymerized materials are highly cross-linked oligomers. The gel permeation chromatography showed that the polymers have low molecular weights. The thermal degradation mechanisms were studied and found that at ignition they produced good char residue. They had glass melting point temperatures ranging from 11 to 31 C which is thermally stable below 200 C. © 2017 Published by Elsevier Ltd.

Keywords: Renewable resources Biopolymers Epoxidized soybean oil Cross-linked polymerization Phosphorus containing polymer

1. Introduction In the 21st century, polymer materials are used in many areas of everyday life; mostly they are produced from fossil sources. Because of their broad usage polymers make a significant contribution to increasing the amount of solid waste in the environment. Therefore, in the polymer science usages of monomers from petroleum products are an important topic. Because of increasing the prices global warming and other environmental problems are changing from fossil feedstock to renewable resources and they can considerably contribute to a sustainable development in the future. New technologies which consider the use of renewable, biobased and more cost-effective resources in the production of biopolymers gave some valuable results [1]. Vegetable oils (VOs) were found to be a good replacement of petroleum products and syntheses of various biodegradable polymers have been reported. Their great utility lies in the fact that the much of the oils present in plants are unsaturated (i.e., contain reactive C¼C) and triglycerides (tri-esters of glycerol, Fig. 1a). In addition, some of the other raw VOs, such as Vernonia oil (Fig. 1b) and Castor oils (Fig. 1c) already contain more numbers of epoxy and hydroxyl groups.

* Corresponding author. E-mail address: [email protected] (Y. Hu). http://dx.doi.org/10.1016/j.polymdegradstab.2017.04.022 0141-3910/© 2017 Published by Elsevier Ltd.

These renewable chemical functionalities allow a range of polymerization chemistry to be practiced leading to a wide variety of biodegradable polymers [2]. For these reasons, nowadays, there is a growing effort to produce polymers based on renewable resource VOs. These biopolymers have some advantages compared with that of polymers from petroleum-based monomers because mostly they are biodegradable and cheaper. In this connection, SBO is one of our favorite raw material because of it has saturated and unsaturated environmental friendly renewable fatty acids (80e85%) (Fig. 1a) and it is cheap along with societal advantages [2,3]. It contains approximately 4.6 reactive carbon-carbon double bonds per triglyceride with “cis” configuration and allows the SBO for the development of various applications. Recent literature was evidenced it and reported various biodegradable polymers at either double bond itself or by converting another reactive group, like epoxy, oxidation, etc. But the direct polymerization of unsaturated triglycerides is rarely successful. Therefore, the polymerizations of triglycerides are preferably done by attaching a polymerizable group to the triglyceride, mostly at active double bond sites [4e11]. Herein, SBO has already proven useful as plastic materials when converted using chemical techniques. All these reports also concluded that triglyceride polymers are expected to play a key role in the 21st century for the synthesis of biodegradable polymers from renewable sources.

C.S.R. Gangireddy, Y. Hu / Polymer Degradation and Stability 140 (2017) 156e165

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Fig. 1. a) Structure of Soybean oil (SBO) is an example of triglyceride molecule; the major component of vegetable oils and reactive positions in triglycerides: (i) ester groups, (ii) allylic positions, (iii) a-positions of ester groups and (iv) C¼C double bonds; b) Structure of Vernonia oil; c) Structure of Caster oil.

In this connection, epoxidized fatty oils can be used in various applications as stabilizers and plasticizers in polymers, as additives in lubricants, or as components in plastics and their derivatives have shown a promising effect when used as reactive resins [12e17]. Along the fatty acid chain of SBO, it has more reactive oxirane rings (epoxy soybean oil, ESBO) which are produced from simple epoxidation of unsaturation, and provides a more energetically favorable site for further chemical modification reactions [2] and permit to introduce polymerizable groups [18]. In addition, water-soluble anti-cancer drug doxorubicin hydrochloride (Dox) carrier anionic polymers also prepared from ESBO to enhance Dox toxicity against multidrug-resistant (MDR) cancer cells [19]. Industrially important polyols that are used in polyurethane materials [20e22] and potentially useful polymers in paints, coatings, food, medicine and many other areas [23e27] are also prepared from ESBO. Recently, chemically resistant, thermally stable, transparent and potentially biodegradable novel pressure-sensitive adhesives (PSAs) are prepared from ESBO and its derivatives [5e7]. Therefore, herein, we report the ring-opening and additionsubstitution polymerization reactions to give polymerized ESBO (PESBO) with various types of phosphorus-containing monomers using FBA as Lewis acid catalyst in tetrahydrofuran (THF) and the molecular weight increase was monitored by using gel permeation chromatography (GPC). The structures of the resulted polymers were characterized and confirmed using FT-IR, 1H NMR, 13C NMR and 31P NMR. The thermal properties of resulted polymers were investigated by differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) and observed more char residue at ignition.

anti-oxidants. At the same time there are also commercially available colorless ESBO from a local grocery store with an epoxy value 6.71%, viscosity of 360 (20 C, CST) and acid value was 0.29 mg KOH/ sample. But for better results, we used the fresh ESBO by selfprepared from SBO. Anhydrous ethanol, phenyl phosphonic dichloride (PhP(O)Cl2), FBA and Magnesium (Mg) turnings were purchased from Sigma-Aldrich were used as supplied. All other chemicals and solvents were procured from Hefei Jiangfeng Chemical Industry Co. Ltd. (Anhui, China) of reagent grade and were used without further purification.

2.2. Methods 2.2.1. Synthesis of ESBO At beginning, synthesis of ESBO was performed as shown in Fig. 2. 100 g of soybean oil (0.53 mol), and 22 g of 90% formic acid (0.48 mol) were taken into a 500 mL two-neck round-bottom flask, which was fitted with mechanical stirrer and pressure equalizing dropping funnel which was filled with 66.1 g (0.58 mol) of 30% H2O2 (Scheme 1). With agitation, hydrogen peroxide (H2O2) was added slowly drop by drop during the first 30 min of reaction at 50e55 C. While the addition of peroxide the reaction temperature was increased and maintained at 60 C for further 6 h. After that, the reaction mixture was cool down, dissolved in ethyl acetate and neutralized by washing several times with distilled water from separatory funnel. The organic layer was separated and dried over anhydrous magnesium sulfate (MgSO4) and removed by rotary evaporator. Further, dry was performed in a vacuum oven at 120 C for 10 h to give a yellow colored ESBO and used for further reactions.

2. Experimental and methods 2.1. Materials The following materials were used in the experiments; commercial refined, bleached, and deodorized (RBD) SBO was obtained from a local grocery store with a viscosity of 65.5278 cps, (acid value was 0.024 mg KOH/sample) and it did not contain any added

2.2.2. Synthesis of bis(4-fluorophenyl)(phenyl)phosphine oxide (BFPPO) and bis(4-hydroxyphenyl)(phenyl) phosphine oxide (BHPPO) monomers The BFPPO and BHPPO monomers were synthesized according to the reported procedure from 1-bromo-4-fluorobenzene followed by the Grignard reaction [28].

158


Scheme 1. Synthesis of ESBO and SOP.

2.2.3. Synthesis of soybean oil polyols (SOP) Took excess of ethanol (14 g, 0.3 mol) to avoid oligomerisation of ESBO and 1 g of fluoroboric acid etherate (FBA) into the two-necked round bottom flask which is fitted with mechanical stirrer and pressure equalizing dropping funnel and was heated in an oil bath. After the desired temperature (40 C) reach under vigorous stirring, added dropwise 60.0 g of ESBO (0.25 mol) in ethanol (20 mL) through a separatory funnel for 15 min (Scheme 1). After all the ESBO was added, continued the stirring for further 20 min and after that, the excess ethanol was removed by rotary evaporator and reaction mixture was cooled down and neutralized to litmus by adding ammonia solution (30%). Then the solution was taken into the separatory funnel by ethyl acetate and washed the organic layer three times with water. The combined organic layer was dried over anhydrous MgSO4 and removed by rotary evaporator. Further, dry was performed in a vacuum oven at 90 C for 10 h to give a dark yellow colored SOP and as it is used for further polymerization reactions. 2.2.4. Synthesis of bis(2-(4-(2-hydroxyethoxy)phenoxy)ethyl) phenyl phosphonate (BHEPPPO) BHEPPPO was in situ synthesized according to the literature procedure (Scheme 2) [28] as follows: to a mixture of 2,20 -(1,4phenylenedioxy)diethanol (19.82 g, 0.1 mol) and triethyl amine (TEA, 14 mL, 0.1 mol) in THF (30 mL) was added a solution of PhP(O) Cl2 (7.09 mL, 0.05 mol) in THF (10 mL) under nitrogen atmosphere at 0e10 C over a period of 30 min. After completion of addition was raise up the temperature, stirred for 2 h more at 45 C and

formation of BHEPPO were ascertained by TLC analysis. The TEA hydrochloride was removed by filtration and the filtrate was dried over anhydrous MgSO4 and removed the solvent under vacuumed distillation by rotary evaporator and obtained the crude BHEPPPO. It was further purified by column chromatography using ethyl acetate: hexane (1:3) as eluent and was characterized by IR, 1H-, 13C-, and 31P NMR spectral data. 2.2.5. Synthesis of PESBO-I/II polymers from ESBO In a typical procedure, ESBO 14.63 g (0.015 mol) and 1 g of FBA in 30 mL of isopropanol and 1 g of H2O were taken into two-necked round bottom flask attached to mechanical stirrer and pressure equalizing dropping funnel under vigorous stirring and was heated in an oil bath. After the desired temperature (80 C) was reached, BHEPPPO (7.78 g, 0.015 mol)/BHPPO (4.65 g, 0.015 mol) in 10 mL isopropanol was added dropwise through dropping funnel in 20 min. After complete addition of BHEPPPO, stirring was continued for further 5 h, then cooled and added distilled water. The obtained oily layer was extracted with ethyl acetate and then washed with water three times to neutralize. The combined organic layer was separated, dried over anhydrous MgSO4 and rotary evaporated the solvent and further dried under vacuum oven at 90 C for 10 h obtained high viscous PESBO-I/II polymers respectively with lower molecular weight (Scheme 3). 2.2.6. Synthesis of PESBO-III polymers from SOP The cross-linked polymerization reaction of PESBO-III (Scheme 4) was followed according to the reported procedure [29]. To a

Scheme 2. Synthesis of BHEPPPO.


159

Scheme 3. Synthesis of cross-linked polymers of ESBO-I & II.

Scheme 4. Synthesis of the cross-linked polymer of ESBO-III.

500 mL, three-necked round-bottomed flask equipped with mechanical stirrer, pressure equalizing dropping funnel and nitrogen inlet/outlet charged with equimolar amounts of SOP (6.316 g, 0.02 mol), BFPPO (6.286 g, 0.02 mol) and K2CO3 (1.04 g, 0.0075 mol) in N,N-dimethyl acetamide (DMAc, 20 mL) and toluene (40 mL). The mixture was then heated to reflux (140e150 C) for 3 h to remove the water azeotropically with toluene. After collecting the toluene in pressure equalizing dropping funnel, the reaction temperature was increased to 180 C and maintained for another 6 h. After cooling to room temperature, the reaction mixture was neutralized with 2N HCl. The obtained oily layer was extracted with ethyl acetate and then washed with water several times to remove any

inorganic impurities. The combined organic layer was separated, dried over anhydrous MgSO4 and rotary evaporated the solvent and further dried under vacuum oven at 80 C for 10 h obtained high viscous PESBO-III polymer. 2.2.7. Synthesis of PESBO-IV polymer from ESBO and Grignard reagent The PESBO-IV was synthesized from ESBO and Grignard reagent which was prepared in situ via Grignard reaction. To a 500 mL fourneck round-bottom flask equipped with mechanical stirrer, three pressure equalizing dropping funnels, and N2 inlet/outlet, magnesium turnings (1.215 g, 0.05 mol) and molecular iodine (catalytic

160


amount, 0.006 g) were dissolved in dry THF (50 mL). The mixture was stirred at 60 C for 30 min and p-dibromo benzene (5.898 g, 0.025 mol) in dry THF (20 mL) was added slowly from one of the dropping funnels over a period of 10 min. After the addition, the mixture was stirred for an additional 3 h at reflux temperature until a cloudy gray solution was obtained. After that, the reaction mixture was cooled to 0e5 C and phenyl phosphonic dichloride (1.8 mL, 0.0125 mol) in dry THF (20 mL) was added through a second addition funnel. During the addition, bubbles started and the cloudy gray solution became a clear dark brown solution. Stirring was continued for further 4 h at room temperature (rt) to obtained phosphorylated Grignard reagent. To this Grignard solution added the ESBO (12.25 g, 0.0125 mol) in a period of 20 min. After the ESBO addition, the reaction temperature was raised to rt and stirred for further 3 h. After the completion of the reaction, cool, filter the excess Mg turnings and added water. The obtained PESBO-IV polymer was extracted with ethyl acetate and then washed with water three times. The combined organic layer was separated, dried over anhydrous MgSO4 and rotary evaporated the solvent and further dried under vacuum oven at 90 C for 10 h obtained high viscous PESBO-IV polymer with lower molecular weight (Scheme 5).

2.3. Characterization 2.3.1. Potentiometric titration The number of hydroxyl groups at the side chain of SOP was determined according to ASTM E 1899-97 method (Equ. (1)) by potentiometric titration using 0.1 N tetrabutylammonium hydroxide (Bu4NOH) and p-toluenesulfonyl isocyanate (TSI) reagent at rt on potentiometric endpoint seeking automatic titrator of Metrohm 888 titrando potentiometry bridge (Swiss made) and 801 stirrer (Fig. 3).

ðV V1 Þ N 56:106 Hydroxy number ðOHÞ ¼ 2 Sample:g

(1)

Where: N ¼ concentration of Bu4NOH in meq/mL, V1 ¼ mL Bu4NOH to the second potentiometric end point, V2 ¼ mL Bu4NOH to the

second potentiometric end point, and Sample.g ¼ mass of sample in grams. 2.3.2. Infrared spectroscopy Functional groups of all newly synthesized dry compounds were confirmed by using Fourier Transform Infrared (FT-IR) Spectroscopy. KBr as reference scanned at the range of 400e4000 cm1 for 50 scans at a spectral resolution of 16 cm1 on Nicolet 6700 FT-IR spectrophotometer. 2.3.3. Nuclear magnetic resonance (NMR) spectroscopy Proton nuclear magnetic resonance (PMR), carbon magnetic resonance (CMR) and phosphorus nuclear magnetic resonance (31P NMR) spectrum were performed on Bruker AV400 NMR spectrometer (400 MHz) operating in the Fourier transform mode at 400, 100 and 161.89 MHz respectively with a 5 mm probe. Deuterated chloroform (CDCl3) was used as a solvent and the chemical shift values were measured in delta (d) units from tetramethylsilane (TMS) for PMR, CMR, and H3PO4 for 31P NMR. Each spectrum was Fourier Transform, phase-corrected, and integrated using MetRe-C 2.3a software. 2.3.4. GPC GPC profiles were obtained on a Waters 2410 differential refractometer including a 1515 water HPLC pump, an automated injector, a column heater, and with two Styragel columns (HT3 and HT4, Waters Co.) using wavelength of 670 nm. Signals generated from a Water 2487 dual l absorbance detector and N, N-dimethylformamide was used as the mobile phase at a flow rate of 1 mL/ min, and columns were maintained at 40 C. The samples were brought into solution with DMF from Sigma-Aldrich at a known concentration near 5 ppm. 2.3.5. DSC DSC thermograms of the test samples were recorded using a Q2000 DSC Instrument (TA Instruments Inc.). Typically about 5 mg of the PESBO polymer samples were accurately weighed in an aluminum pan and sealed with pin perforated lids. The DSC oven was ramped at 10 C/min to 110 C to eliminate thermal history and

Scheme 5. Synthesis of the cross-linked polymer of ESBO-IV.


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possible moisture. A DSC-refrigerated cooling system was used to equilibrate the sample at 90 C, from 110 C at a rate of 5 C/min. Data were recorded while the oven temperature was raised from 90 to 800 C at a rate of 5 C/min. The DSC method applied an inert atmosphere by purging the oven with nitrogen at 55 mL/ min. Thermal Advantage and Universal Analysis software provided by TA instruments were used for data analysis. 2.3.6. TGA Thermo Gravimetric Analysis (TGA) was carried out using a Q5000 thermoanalyzer instrument (TA Instruments Inc., New Castle, DE) under a flow of 20 mL/min to measure the weight loss of the PESBO samples under a flowing nitrogen atmosphere and 15 mg of PESBO sample was used in the TGA. The samples were heated from 30 to 800 C at a heating rate of 10 C/min and the weight loss was recorded as a function of temperature. All the above experimental data in this paper were interpreted using SigmaPlot 10.0 software.

Fig. 3. Typical potentiometric titration curve for determination of hydroxyl number using 0.1 N Bu4NOH and TSI reagent.

3. Results and discussion 3.1. Synthesis of ESBO To prepare various polymeric materials from soybean oil, epoxidation of double bonds with hydrogen peroxide is the easier and useful reaction [30e35]. Herein we synthesized the ESBO using formic acid and H2O2 which are producers with an average of 4e5 epoxy groups per triglyceride (Scheme 1). The epoxidation of soybean oil using in situ generated peroxy acid (Fig. 2) could be carried out at a moderate temperature of about 60 C. The formation of epoxide rings on the fatty acid side chains of soybean oil was evident that the unsaturated C¼C stretching band at 3009 cm1 was disappeared and generated the oxirane C-O twin bands at 820 and 850 cm1 (Fig. 4). In addition, the reaction completion was further confirmed by 1 H NMR spectra of ESBO, where the peak at 5.34 ppm (-CH- protons of unsaturation) decreased the peak intensity and appear twin peaks in the range 2.93e3.09 ppm (-CH- protons of the epoxy ring) (Fig. 5). These IR and NMR spectrum of our ESBO product are the same as that observed for a commercially available ESBO standard. 3.2. PESBO polymers synthesis and spectral identification Many nucleophilic reagents are well known in the literature for addition to an oxirane ring, which were resulting in ring opening polymerization. But, the rate of ring opening of oxirane ring in ESBO is a slower rate, and which are requires any acid catalyst to improve the rate of ring opening. Therefore, the polymerization pathways of PESBO polymers from ESBO were illustrated with various nucleophiles in Scheme 3 and 5. We reported the ESBO ring opening polymerization by a one-pot

Fig. 4. IR Spectrum of SBO, ESBO, SOP and PESBO polymers.

and one-step process using FBA as a catalyst, due to its high catalytic activity towards oxirane ring opening that promotes the formation of the polymer through cross-linked polymerization. The proton of the catalyst attacks the epoxide ring to afford ring opening followed by a nucleophilic attack at carbon which sterically less. SOP, which prepared using ethanol as a nucleophile by epoxy ring opening of triglyceride (Scheme 1) using FBA as catalyst was used as a monomer in the synthesis of PESBO-III polymer. The number of OH groups in SOP was measured as 201.4563 mg KOH/g

Fig. 2. Schematic presentation of synthesis of ESBO.

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Fig. 6.

13

C NMR Spectrum of SBO, ESBO, PESBO-I, II and IV polymers.

Fig. 5. 1H NMR Spectrum of SBO, ESBO, SOP and PESBO polymers.

(Fig. 2) and confirmed that each side chain of triglyceride molecule possesses unit hydroxy functionality to total 3.9 OH functionality. It is higher than the theoretical value of 192 mg KOH/g. By utilizing this SOP as a monomer, PESBO-III polymer was accomplished by condensation with BFPPO using K2CO3 as catalysis at 180 C (Scheme 4). The condensation polymerization was not observed at lower reaction temperature, but at higher temperature found a good yield of PESBO-III polymer. The synthetic process of PESBO-IV was followed by the Grignard reaction (Scheme 5). At first, the Grignard reagent were prepared by in situ under nitrogen atmosphere and followed by the consecutive addition of ESBO to it obtained the desired polymer effectively. Here also observed the cross-linked polymerization under GC analysis because of higher nucleophilic activity of Grignard reagent towards ESBO. As the ring opening reaction completed the oxirane C-O twin bands at 820 and 850 cm1 were disappeared in all PESBO polymers and generated broad bands in the region of 3468e3362 cm1 of O-H stretching frequencies. The general absorption bands of aromatic C¼C was observed at 1610-1500 cm1 and also the phosphate groups (P¼O) stretching frequencies are observed at 12491234 cm1 (Fig. 4). These were further confirmed by 1H NMR spectra of PESBO polymers, where the twin peaks in the range 2.86e3.13 ppm (-CHprotons of the epoxy ring) disappeared and additional peaks appeared in the range of 3.26e3.74 ppm (protons attached to the carbon of -CHOH and OH group) (Fig. 5). The PESBO polymers formation was furthermore confirmed by carbon NMR (Fig. 6). The distinguishable carbon peaks at 127e130 ppm corresponding to unsaturated carbons in side chains of triglycerides of SBO are disappeared by epoxidation and appeared at 53e57 ppm which is indicated that formation of oxirane rings in ESBO. In the cross-linked polymerization of ESBO with various nucleophiles these oxirane carbons peaks are shifted to 60e70 ppm by ring opening and in addition peaks in the range of 99e164 ppm appeared which are corresponding to aromatic carbons indicated that polymerization of ESBO. In all the newly synthesized PESBO polymers the phosphate ester group frequencies appear between 31.82 and 2.48 as multiplets (Fig. 7). The multiplet nature and various chemical shift values of the phosphorus element are due to the presence of

Fig. 7.

31

P NMR Spectrum of PESBO polymers.

various chemical environments around the phosphine oxide group. The spectroscopic results presented above successfully characterized the PESBO polymers synthesized using the ESBO. These confirmed complete disappearance of the signature of the epoxy linkage, formation of the hydroxyl groups following the cross-link addition process. Along with the above mentioned FT-IR and NMR analysis, the GPC, DSC and TGA results provided further evidenced. 3.3. GPC determination of the molecular weight of PESBO polymers The molecular weight value of PESBO polymers was determined by GPC and the chromatogram of cross-linked polymers shown in Fig. 8. The results indicated that the obtained polymers having less molecular weight (Table 1). 3.4. Thermal stability and structure relationships The thermal stability temperatures of newly synthesized PESBO polymers after extraction were measured by DSC and they are shown in Fig. 9 and the results are summarized in Table 1. The DSC


Fig. 10. TGA Thermograms of the PESBO polymers weight loss versus temperature (under N2 atmosphere).

Fig. 8. GPC chromatograms of PESBO polymers.

Table 1 DSC derived Tg1, Tg2, and Tm and number average molecular weight (Mn) of PESBO polymers. Polymer

PESBO-I PESBO-II PESBO-III PESBO-IV

DSC Tg1 ( C)

Tg2 ( C)

Tm ( C)

30.2 34.1 12.2 39.5

13.2 12.2 9.8 20.9

31.2 17.0 21.2 1.3

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GPC Mn [g/mol] 11200 8700 8200 7600

Fig. 9. DSC analysis graphs of polymers of PESBO polymers.

for PESBO polymers showed that are present three phases; two amorphous phases (Tg1, Tg2) and one crystalline phase (Tm). These thermal behaviors of the resulted PESBO polymers depend on the type of nucleophile used in epoxy ring opening. The first glass transition (Tg1) temperatures corresponded to the amorphous PESBO polymers and the second glass transition (Tg2) temperatures were attributed to amorphous rigid polyesters phases. To better understand the thermal properties of PESBO polymers, TGA was used to investigate their thermal decomposition behavior in a nitrogen atmosphere. Fig. 10 shows the TGA curves for the PESBO polymers and the thermal stability values are presented in

Table 2 Thermal stability data of PESBO polymers prepared from ESBO by various nucleophiles. Sample

Stability

T10 ( C)

T50 ( C)

T80 ( C)

TDecom ( C)

Char yield (%)

PESBO-I PESBO-II PESBO-III PESBO-IV

205 200 252 110

321 259 362 248

374 354 416 341

421 421 442 442

486 487 475 487

2.91 2.90 0.63 8.75

Table 2. All the polymers are thermally stable under 200 C, except PESBO-IV, it's showing below 110 C. For the early instability of later, one should be easily elimination of water molecules from polymer chain followed by formation of extending conjugation of the aromatic system (Scheme 6d). It could be also supported that the stability of PESBO-II, which shown higher stability than remaining others because of the lack of the hydroxy group on the chain (Scheme 6c). After that, PESBO-I, PESBO-II, and PESBO-IV oligomers showed two stages of distinct weight loss decompositions, such as a fast first decomposition in the range of 352e400 C and the second fast decomposition appears in the range of 477e487 C respectively and on the other hand PESBO-II was exhibited only in single stage decomposition. The second stage decompositions of the former group of polymers probably come due to the loss of aromatic polymer backbone. On the other hand, the obtained polymers consist of a highly cross-linked polymer. Therefore, their decomposition temperature is above 400 C at the heating rate of 20 C/min. This step corresponds to degradation and char formation of the cross-linking polymer structure. Finally, all the samples were completely decomposed at around 490 C with the various percent of char yield formation of the crosslinking polymer network; and due to oxidation of the char residues (Table 2). Table 2 lists the TGA results for the PESBO polymers. T10, T50, T80, and TDecom are the temperatures at 10, 50 and 80% weight loss. T10, which generally lies in stage-I, is used to evaluate the thermal stability of the polymers. T50 in stage-II indirectly reflects the consistency of the cross-linking structure of the polymer. In the combustion test, all the PESBO polymers are produced more char residue. A conventional combustion test was performed at Bunsen burner by taking the polymers in a nickel spatula and observed char residue with lower flame. These results are also observed in the TGA thermogram.

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Scheme 6. Schematic illustration of the possibility of water elimination of newly synthesized oligomers.

4. Conclusions We have developed novel cross-linked oligomers from ESBO and SOP of renewable SBO by ring-opening and addition-substitution polymerization reactions respectively with phosphoruscontaining nucleophiles using FBA as Lewis acid catalyst in THF. All the newly synthesized PESBO oligomers structures are well characterized by using FT-IR, 1H NMR, 13C NMR and 31P NMR and confirmed the formation of polymers GPC. The molecular weights of resulted PESBO polymers are increased along the nucleophile molecular weight increases. The thermal properties of PESBO polymers were tested and they showed that the formation of crosslinked polymerization. In a thermal analysis of PESBO polymers showed stability at 200 C and subsequent oxidation char residues producing at 400 C above. By the addition of phosphorus element to the polymers of SBO, the charring property was improved. The

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