synthesis and characterization

J Polym Res (2017) 24:57 DOI 10.1007/s10965-017-1217-4

ORIGINAL PAPER

Aromatic polyesters containing pendent 4-(phenylsulfonyl)phenyl groups: synthesis and characterization Snehalata P. Bapat 1,2 & Sushilkumar A. Jadhav 1,3 & Nitin G. Valsange 1 & Bhausaheb V. Tawade 1 & Pandurang N. Honkhambe 1 & Nayaku N. Chavan 1 & Prakash P. Wadgaonkar 1

Received: 27 November 2016 / Accepted: 3 March 2017 # Springer Science+Business Media Dordrecht 2017

Abstract A new bisphenol, 1,1-bis-[(4-hydroxyphenyl)-1-(4phenylsulfonyl)phenyl)]ethane (DPSBP) was synthesized starting from diphenylsulfide and was characterized by spectroscopic methods. DPSBP was polycondensed with isophthalic acid chloride (IPC), terephthalic acid chloride (TPC) and a mixture of IPC and TPC (50:50 mol%) by phase-transfer catalysed interfacial polymerization method to obtain aromatic polyesters containing pendent 4-(phenylsulfonyl)phenyl groups. A series of copolyesters was also obtained by polycondensation of varying molar proportions of DPSBP and bisphenol-A (BPA) with TPC. (Co)polyesters exhibited inherent viscosities in the range 0.56–1.57 dLg−1 and number average molecular weights (Mn) were in the range 28,650–80,230 g/mol. Polyesters dissolved readily in common organic solvents such as dichloromethane, chloroform, tetrahydrofuran and aprotic polar solvents such as N-methylpyrrolidone, and N,N-dimethylacetamide. Tough, transparent and flexible films of polyesters could be cast from their chloroform solutions. X-Ray diffraction studies indicated amorphous nature of aromatic polyesters. Polyesters showed Tg

Electronic supplementary material The online version of this article (doi:10.1007/s10965-017-1217-4) contains supplementary material, which is available to authorized users. * Prakash P. Wadgaonkar [email protected] 1

Polymers and Advanced Materials Laboratory, Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune, Maharashtra -411 008, India

2

MIT Academy of Engineering, Alandi, Pune, Maharashtra 412105, India

3

Department of Chemistry and Nanostructured Interfaces and Surfaces (NIS) Centre, University of Torino, Via P. Giuria 7, Torino 10125, Italy

values in the range 223–257 °C while T10 values were in the range of 469–484 °C indicating their excellent thermal stability. Keywords Aromatic polyesters . Solubility . Thermal stability . Bulky pendent group

Introduction Aromatic polyesters are an important class of high performance polymeric materials which exhibit high thermal stability, good mechanical properties and chemical resistance. Consequently, they find applications in aircraft, automobile and electrical industries [1, 2]. However, rigid backbone structure and strong interchain interactions present in aromatic polyesters manifest into their high transition temperatures (Tg and Tm) and limited solubilities in common organic solvents which results in their poor processability characteristics [3, 4]. To surmount these limitations, the following approaches have been employed: a) incorporation of flexible spacers in the backbone; b) introduction of bent or ‘crankshaft’ units in the backbone and c) introduction of bulky or flexible side groups to the polymer chain [5–35]. The introduction of these structural features weakens the intermolecular forces between polymer chains and consequently polymers with improved solubility and processability characteristics are generally obtained. In the previous reports from our laboratory, we studied the effect of incorporation of bulky pendent groups such as biphenyl [36], naphthyl [37] or decahydronaphthalene [38] on solubility and thermal properties of aromatic polyesters. We wish to report herein synthesis of a new bisphenol, 1,1-bis-[(4hydroxyphenyl)-1-(4-phenylsulfonyl)phenyl)]ethane (DPSBP), containing bulky pendent 4-(phenylsulfonyl)phenyl group. Further, interfacial polycondensation of DPSBP with isophthalic

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acid chloride (IPC), terephthalic acid chloride (TPC), and a mixture of IPC and TPC (50:50 mol%) was carried out to form a series of new aromatic polyesters containing pendent 4-(phenylsulfonyl)phenyl groups. Copolyesters were also synthesized by polycondensation of varying molar proportions of DPSBP and bisphenol-A (BPA) with TPC. The effects of incorporation of pendent 4-(phenylsulfonyl)phenyl groups on the solubility and thermal properties of polyesters were investigated.

were further dried at 70 °C for 5 days under reduced pressure to obtain films for XRD studies. Thermal gravimetric analysis (TGA) was conducted on PerkinElmer TGA-7 at a heating rate of 20 °C min−1 under nitrogen atmosphere. DSC analysis was performed on TA instruments DSC Q 10 at a heating rate of 20 °C min−1 under a nitrogen flow rate of 50 cm3 min−1. Synthesis of monomer

Experimental Materials Diphenylsulfide, 3-mercaptopropionic acid, bisphenol-A, and benzyltriethyl ammonium chloride (BTEAC) (Aldrich, USA) were used without further purification. Aluminium chloride, potassium carbonate, methanol, acetonitrile, 30% hydrogen peroxide and phenol (S.D. Fine-Chem., India) were used without further purification. Acetyl chloride and carbon disulfide (from Merck) were purified by distillation before use. Dichloromethane (S.D. Fine-Chem., India) was dried over calcium hydride and purified by distillation. 4-Acetyl diphenylsulfide [39] and 4-(phenylsulfonyl)acetophenone [40] were prepared according to reported procedures. TPC and IPC were synthesized by standard procedures and were purified by distillation under reduced pressure before use [41]. Other solvents and reagents were purified by standard procedures [42]. Measurements FTIR spectra were recorded on a Perkin Elmer Spectrum GX spectrophotometer. 1H and 13C NMR spectra were recorded using a Bruker 200 or 400 MHz spectrometer at operating frequencies of 200 or 400 MHz for 1H and 50 or 100 MHz for 13C spectra, respectively. HRMS of DPSBP was recorded on a Thermo Scientific Q-Exacative, Accela 1250 pump. Inherent viscosity (ηinh) measurments of polyesters were carried out with an Ubbelohde suspended level viscometer on Schott Gerate CK-160 automatic viscometer using 0.5% (w/v) solution of polyester in chloroform at 30 ± 0.1 °C. The solubility of polyesters was measured at 3% (w/v) concentration in different organic solvents at room temperature. Molecular weight measurements of polyesters were performed on ThermoFinnigan make GPC with polystyrene as the calibration standard and chloroform as an eluent. Polyester (5 mg) sample was dissolved in chloroform (5 mL) and filtered through 0.45 μ filter. X-Ray diffraction analysis of polyester films was carried out on a Rigaku Dmax 2500 X-ray diffractometer with a tilting rate of 2° min−1. Polyester was dissolved in chloroform and the solution was filtered on a petri dish; solvent was evaporated gradually at 40 °C in an oven, and the semidried films

Synthesis of 1,1-bis-[(4-hydroxyphenyl)-1-(4-phenylsulfonyl) phenyl)]ethane (DPSBP) Into a 250 mL two necked round bottom flask equipped with a magnetic stirring bar, a HCl gas inlet, and a reflux condenser were added 4-(phenylsulfonyl)acetophenone (25.0 g, 0.096 mol), phenol (100 g, 1.06 mol) and 3mercaptopropionic acid (1 mL). Anhydrous HCl gas was bubbled through the reaction mixture at 60 °C for 8 h. At the end of reaction, excess phenol was distilled out under reduced pressure. The reaction mixture was extracted with ethyl acetate (500 mL) and the ethyl acetate solution was washed repeatedly with aqueous sodium bicarbonate solution, brine and water and dried over anhydrous sodium sulfate. Ethyl acetate was evaporated off to obtain a brownish solid which was purified by Soxhlet extraction using toluene to obtain pure 1,1-bis-[(4hydroxyphenyl)-1-(4-phenylsulfonyl)phenyl)]ethane. Yield =16.53 g (40%). m.p. = 260 °C. 1 H NMR (400 MHz, DMSO-d6) δ ppm: 9.32 (s, 2 H, phenolic –OH), 7.95 (d, J = 7.3 Hz, 2 H), 7.85 (d, J = 7.9 Hz, 2 H), 7.74–7.56 (m, 3 H), 7.25 (d, J = 8.5 Hz, 2 H), 6.77 (d, J = 7.9 Hz, 4 H), 6.65 (d, J = 8.5 Hz, 4 H), 1.99 (br. s., 3 H). 13 C NMR (100 MHz, DMSO-d6) δ ppm: 156.2, 155.5, 141.3, 138.4, 138.3, 133.7, 129.8, 129.5, 129.2, 127.3, 127.0, 114.7, 51.0, 30.1. HRMS [ESI: Figure (S1)] m/z calculated for C26H22O4S (M + Na): 453.1136; found: 453.1131. Synthesis of polyesters A representative procedure for the synthesis of polyesters is given below: Polymerization was carried out in a 100 mL two necked round-bottom flask equipped with a mechanical stirrer. DPSBP (2.15 g, 5.0 mmol) was dissolved in 10 mL of 10 mmol aqueous solution of sodium hydroxide. The mixture was stirred at 10 °C for 1 h. Next, BTEAC (30 mg) was added to the reaction mixture and stirring was continued. After 30 min, solution of isophthaloyl chloride (1.02 g, 5 m mol) in 20 mL of dichloromethane was added to the reaction mixture and the mixture was stirred vigorously at 2000 rpm for 1 h. The aqueous layer was separated and dichloromethane

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Scheme 1 Synthesis of 1,1-bis[(4-hydroxyphenyl)-1-(4phenylsulfonyl)phenyl)]ethane

layer was diluted with additional dichloromethane (10 mL) and poured into excess methanol. The precipitated polymer was filtered and washed repeatedly with water. The polymer was dissolved in chloroform and re-precipitated into methanol. The polymer was filtered, washed with methanol, and dried under reduced pressure at 80 °C for 24 h. The yield of polyester was almost quantitative. A similar procedure was followed for the synthesis of other polyesters and copolyesters.

Results and discussion Monomer synthesis The route for synthesis of DPSBP starting from diphenylsulfide is depicted in Scheme 1. Diphenylsulfide was monoacylated with acetyl chloride in the presence of aluminum chloride to obtain 4-acetyl diphenylsulfide, which

was treated with hydrogen peroxide / potassium carbonate mixture to form 4-(phenylsulfonyl)acetophenone. The two intermediates 4-acetyl diphenylsulfide [39] and 4-(phenylsulfonyl)acetophenone [40] have been reported previously in the literature. Further, DPSBP was synthesized by reaction of 4-(phenylsulfonyl)acetophenone with excess phenol in the presence of dry HCl gas/3-mercapto propionic acid as the catalyst system at 60 °C. The structure of DPSBP was confirmed by 1H and 13C NMR spectroscopy. 1H–NMR spectrum of DPSBP along with the assignments is reproduced in the Fig. 1. The singlet appeared at 9.32 δ ppm is attributed to phenolic –OH. The doublets appeared at 6.77 and 6.65 δ ppm could be assigned to the protons meta and ortho to phenolic –OH groups, respectively. The aromatic protons of diphenylsulfonyl moiety appeared in the range 7.24–7.96 δ ppm. The broad singlet at 1.99 δ ppm could be ascribed to methyl group protons. 13C–NMR spectrum of DPSBP along with the assignments of carbons is represented in Fig. 2.

Fig. 1 1H–NMR spectrum (DMSO-d6) of 1,1-bis-[(4-hydroxyphenyl)-1-(4-phenylsulfonyl)phenyl)]ethane

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Fig. 2

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13

C–NMR spectrum (DMSO-d6) of 1,1-bis-[(4-hydroxyphenyl)-1-(4-phenylsulfonyl)phenyl)]ethane

Polyester synthesis (Co)polyesters containing pendent 4-(phenylsulfonyl)phenyl groups were synthesized from DPSBP and aromatic diacid chlorides (IPC, TPC and IPC + TPC, 50:50 mol%) by phase-transfer catalysed interfacial polycondensation. (Scheme 2) Further, a series of (co)polyesters was synthesized by polycondensation of varying proportions of DPSBP and

Scheme 2 Synthesis of polyester and (co)polyesters containing pendent 4(phenylsulfonyl)phenyl groups

BPA with TPC. The results of polymerization reactions are presented in Table 1. Inherent viscosity (ηinh) of (co)polyesters was in the range 0.56–1.57 dL g−1 indicating formation reasonably high molecular weight polymers. The results of GPC analysis showed number average molecular weights (Mn) and dispersity values (Mn/Mw) in the range 28,650–80,230 g/mol and 2.0–3.1, respectively. (Table 1).

J Polym Res (2017) 24:57 Table 1 Polyester

PES-I PES-II PES-III PES-IV PES-V PES-VI

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Synthesis and characterization of aromatic polyesters containing pendent 4-(phenylsulfonyl)phenyl groups Composition of diols (mol %) DPSBP

BPA

100 100 100 75 50 25

0 0 0 25 50 75

Diacid chloride

TPC IPC TPC:IPC (50:50) TPC TPC TPC

ηinha (dL/g)

1.04 0.56 0.75 1.13 1.16 1.57

Molecular weight b Mn

Mw

62,080 43,490 28,650 63,210 74,670 80,230

1,55,700 86,800 88,800 1,77,000 1,59,000 1,95,700

a

ηinh of polyester was measured with 0.5% (w/v) solution of polyester in chloroform at 30 ± 0.1 °C;

b

measured by GPC in chloroform; polystyrene was used as the calibration standard

c

Measured on DSC at a heating rate of 20 °C/min

d

Measured by TGA at a heating rate of 20 °C/min in nitrogen

The structural analysis of polyesters was carried out by FTIR, 1H–NMR and 13C–NMR spectroscopic techniques. A representative FT-IR spectrum of the polyester derived from DPSBP and TPC is presented in Fig. 3. Ester carbonyl band of polyesters was observed at 1736 cm−1. The bands observed at 1320 cm−1 and 1165 cm−1 are attributed to asymmetric and symmetric stretching of the sulfone group, respectively. A representative 1H–NMR spectrum of polyester obtained from DPSBP and TPC along with assignments is

Fig. 3 FTIR spectrum of polyester (PES-I) derived from DPSBP and TPC

Mw/Mn

Tgc (°C)

T10d (°C)

2.5 2.0 3.1 2.8 2.1 2.4

260 223 245 257 252 246

484 477 469 477 477 479

shown in Fig. 4. The protons of TPC moiety (13, 14) showed a singlet at 8.32 δ ppm. The protons 4, 8 and 3, 9 of DPSBP moiety exhibited two separate doublets at 7.97 and 7.87 δ ppm, respectively whereas the protons 10, 2, 11 appeared as a multiplet in the range 7.21–7.13 δ ppm. The protons 5, 6, 7 appeared as a multiplet in the range 7.58–7.50 δ ppm. The protons 12 appeared as a doublet at 7.31 δ ppm. The methyl protons 1 of DPSBP moiety exhibited a broad singlet at 2.22 δ ppm.

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Fig. 4 1H–NMR spectrum (CDCl3) of polyester (PES-I) derived from DPSBP and TPC 13

C–NMR spectrum of the polyester obtained from DPSBP and TPC along with the assignment of carbons is reproduced in Fig. 5. 1 H–NMR spectroscopy was utilized to determine the compositions of copolyesters synthesized with different molar ratios of DPSBP and BPA. In 1H–NMR spectra of copolyesters (e.g. PES-V, containing 50:50 mol ratio of DPSBP and BPA as shown in Fig. 6), the signals in aliphatic region at 2.20 and 1.73 δ ppm were assigned to the methyl group protons ‘1’ of DPSBP moiety and methyl group protons ‘19’ of gemdimethyl group of BPA, respectively. The determination of compositions of co-monomers viz. DPSBP and BPA was carried out from ratio of integrations of peak at 2.20 δ ppm and 1.73 δ ppm. The data in Table 2 indicated that there was a reasonably good agreement between the observed and the feed composition of bisphenol monomers.

Fig. 5

13

Solubility of polyesters The solubility behavior of (co)polyesters in different organic solvents was tested at 3 wt% (w/v). Polyesters containing pendent 4-(phenylsulfonyl)phenyl groups were readily soluble in various organic solvents such as dichloromethane, chloroform, tetrahydrofuran, N-methylpyrrolidone, N,Ndimethylacetamide, etc. and were found to be insoluble in dimethyl sulfoxide. In contrast, polyesters derived from BPA with TPC or IPC are reported to be insoluble in common organic solvents such as chloroform, dichloromethane and tetrahydrofuran [11]. The improved solubility of DPSBPbased polyesters could be attributed to the incorporation of bulky pendent 4-(phenylsulfonyl)phenyl groups into polyester backbone. The bulky pendent 4-(phenylsulfonyl)phenyl groups caused distruption in dense packing of polymer chains

C–NMR spectrum (CDCl3) of polyester (PES-I) obtained from DPSBP and TPC

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Fig. 6 1H–NMR spectrum (CDCl3) of copolyester (PES-V) obtained from DPSBP (50%) and BPA (50%) with TPC

and increased free volume, which assist easy penetration of solvent molecules into the polymer chains leading to enhancement in solubility. X-ray diffraction studies X-Ray diffraction studies were carried out in order to study crystallinity of polyesters based on DPSBP. As shown in Fig. 7, X-ray diffractograms of polyesters exhibited broad halo over 2θ range of 2–40° without noticeable peak features, demonstrating their amorphous nature. The introduction of pendent 4-(phenylsulfonyl)phenyl group into the polymer backbone hindered the close packing of polymers chains which results in amorphous nature of the polyesters. The amorphous nature was also reflected in excellent solubility of these polyesters.

The glass-transition temperatures (Tg) of polyesters were determined by DSC at a heating rate of 20 °C /min under nitrogen atomsphere. Polyesters derived from DPSBP with TPC and IPC exhibited Tg at 260 °C and 223 °C, respectively. The copolyester (PES-III) obtained from DPSBP with a mixture of IPC and TPC (50:50 mol%) showed Tg at 245 °C. The Tg values of copolyesters derived form different molar ratios of DPSBP and BPA with TPC (PES-IV-VI) were in the range 246–257 °C. It is worth mentioning that Tg values of polyesters based on DPSBP and TPC or IPC were noticeably higher than that of corresponding polyesters based on bisphenol-A (Tg of polyester based on BPA-TPC and BPA-IPC are 210 °C and 181 °C, respectively) [43]. The increase in the Tg of polyesters based on DPSBP could be ascribed to the presence of bulky pendent 4-(phenylsulfonyl)phenyl groups which was effective in hindering the segmental mobility of polymer chains.

Thermal properties of polyesters Thermal stability of polyesters was evaluated by thermogravimetric analysis (TGA) in nitrogen atmosphere at a heating rate of 20 °C/min (Fig. 8). The decomposition temperatures at 10% weight loss (T10) of polyesters were calculated from TGA curves and the values are given in Table 1 .T10 values (co)polyesters were in the range 469–484 °C indicating their excellent thermal stability. Table 2

Copolyester composition determined from 1H–NMR spectra

Copolyester PES-IV PES-V PES-VI

Observed DPSBP, mol %

Feed DPSBP, mol %

74 48 21

75 50 25

Fig. 7 X-Ray diffractograms of aromatic polyesters containing pendent 4-(phenylsulfonyl)phenyl groups

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Fig. 8 TGA curves of aromatic polyesters containing pendent 4(phenylsulfonyl)phenyl groups

Conclusions

2.

A new bisphenol, 1,1-bis-[(4-hydroxyphenyl)-1-(4phenylsulfonyl)phenyl]ethane containing pendent 4-(phenylsulfonyl)phenyl group was synthesized. Polyesters and copolyesters containing pendent 4-(phenylsulfonyl)phenyl groups were synthesized by phase transfer-catalyzed interfacial polycondensation of DPSBP and a mixture of different proportions of DPSBP and BPA with aromatic diacid chlorides. (Co)polyesters containing pendent 4-(phenylsulfonyl)phenyl groups were easily soluble in common organic solvents at room temperature and tough, transparent and flexible films could be cast from their chloroform solutions. (Co)polyesters containing pendent 4-(phenylsulfonyl)phenyl groups showed amorphous nature. The T10 values of polyesters were in the range of 469– 484 °C indicating their excellent thermal stability. The introduction of bulky pendent 4-(phenylsulfonyl)phenyl groups was responsible for increase in Tg values of polyesters based on DPSBP compared to BPA-based polyesters. The improved solubility characteristics and excellent thermal stability of polyesters make them promising candidates as processable high performance materials.

10.

Acknowledgements The authors would like to thank Council of Scientific and Industrial Research, New Delhi for the financial support.

11.

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