Synthesis of new polyimidosulfides by Michael addition of bis(1-mercapto-2-ethylether) and amido thiosulfide oligomers

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1 Designed Monomers and Polymers ISSN: (Print) (Online) Journal homepage: Synthesis of new polyimidosulfides by Michael addition of bis(1-mercapto-2-ethylether) and amido thiosulfide oligomers Constantin Gaina & Viorica Gaina To cite this article: Constantin Gaina & Viorica Gaina (2005) Synthesis of new polyimidosulfides by Michael addition of bis(1-mercapto-2-ethylether) and amido thiosulfide oligomers, Designed Monomers and Polymers, 8:2, , DOI: / To link to this article: Published online: 02 Apr Submit your article to this journal Article views: 44 Citing articles: 4 View citing articles Full Terms & Conditions of access and use can be found at

2 Designed Monomers and Polymers, Vol. 8, No. 2, pp (2005) VSP Also available online - Synthesis of new polyimidosulfides by Michael addition of bis(1-mercapto-2-ethylether) and amido thiosulfide oligomers CONSTANTIN GAINA and VIORICA GAINA Institute of Macromolecular Chemistry P. Poni, 41A Grigore Ghica Voda Alley, Iasi RO , Romania Abstract New polyimidosulfides were synthesized by Michael addition reaction of bis(1-mercapto- 2-ethylether) and amido thiosulfide oligomers with various biscitraconimides. The reaction was performed at C in N-methylpyrolidin-2-one and in the presence of tributylamine as a catalyst. The biscitraconimides were prepared by reaction of citraconanhydrides and diamines in glacial acetic acid at reflux. The structures of the resulting polymers were confirmed by elemental analysis, IR and 1 H-NMR spectroscopy. They were characterized by viscometry, solubility, measurements of differential scanning calorimetry and thermal analysis. Keywords: Polyimidosulfide; Michael addition; amido thiosulfide; bis(1-mercapto-2-ethylether); elemental analysis. 1. INTRODUCTION Maleimide polymers have applications in the area of composites due to their excellent thermal properties, chemical resistance and mechanical properties. The major shortcoming of bismaleimide systems is brittleness, which results in low damage tolerance and poor processing characteristics. Various attempts have been made to improve the impact and fracture toughness of polybismaleimide materials. One of the attractive reactions is the Michael addition of nucleophiles such as diamines [1 6], bisthiols [7 10] and bisphenols [11]. We already reported on the synthesis of bismaleimide resins with urethane methylene links [12, 13], poly(aminobismaleimide)s containing parabanic rings [14], bismaleimide prepolymers with diamines [15] and poly(imido-thioether)s [16]. The reaction of bismaleimides with thiols in acid medium generates thiolate anions which can To whom correspondence should be addressed. vgaina@icmpp.tuiasi.ro

3 146 C. Gaina and V. Gaina undergo an addition reaction to the maleimide double bond. A carbanion, able to initiate the anionic polymerization of the bismaleimide [7], was formed. The presence of methyl groups at the maleimide double bonds reduces the possibility of their homo-polymerization through an anionic mechanism, but increases the possibility to obtain linear polymers. In this work, we introduce new polyimidothioethers synthesized by Michael addition reaction of bis(1-mercapto-2-ethylether) with biscitraconimides. 2. EXPERIMENTAL 2.1. Measurements The IR spectra were recorded on a Carl Zeiss Specord M90 spectrophotometer by using the KBr pellet technique. The 1 H-NMR spectra were recorded on a Jeol C60- HL spectrometer using DMSO-d 6 as solvent and tetramethylsilane as an internal standard. Melting and softening points were determined with a Gallenkamp hotblock point apparatus. Thermogravimetric analysis (TGA) was carried out in air with an F. Paulik Derivatograph at a heating rate of 12 C/min. Differential scanning calorimetry (DSC) measurements were done by using a Mettler TA Instrument DSC 12E with a heating rate of 10 C/min, in nitrogen. Thermooptical analysis (TOA) was carried out in air at a heating rate of 9.6 C/min as described [19]. Gelpermeation chromatographic (GPC) analyses were carried out on a PL-EMD 950 Evaporative light detection instrument using N,N-dimethylformamide (DMF) as the eluent and standard polystyrene sample for calibration Reagents and materials The bis(1-mercapto-2-ethylether) (Aldrich) and citraconimide (Aldrich) were used as received. 4,4 -Diaminodiphenylmethane, 4,4 -diaminodiphenylsulfone and 4,4 - diaminodiphenylether were purified by recrystallization from benzene, methanol and acetonitrile, respectively. N-Methyl-pyrolidin-2-one (NMP) was distilled before use. Glacial acetic acid, tributylamine and p-toluidine were used as received General procedure for the preparation of biscitraconimides (1a d) Biscitraconimides 1a d were prepared from diamines (1 mol) with citracon-anhydride (2 mol) in glacial acetic acid, at reflux, according to a method described in literature [17] (Scheme 1). Intermediate bis(amic acid) was cyclodehydrated in situ by refluxing in acetic acid Biscitraconimide 1c A typical procedure for preparation of biscitraconimides was as follows: to a solution of 55 mmol (11.02 g) 4,4 -diaminodiphenylether in 100 ml glacial acetic

4 Synthesis of new polyimidosulfides by Michael addition 147 Scheme 1. acid, 9.9 ml (120 mol) citraconimide in 50 ml glacial acetic acid was added and stirred at room temperature for 1 h. The reaction mixture was heated under reflux for 4 h, then concentrated under reduced pressure and then cooled and precipitated in 200 ml water. The precipitate was filtered and washed with 100 ml 3% Na 2 CO 3 solution, then with water and dried at 80 C for 12 h in a vacuum oven. The yield after recrystallization from acetone was 17 g (80%), mp C. IR spectrum (KBr, cm 1 ): 3120, 1720, 1520, 1420, 1270, 1130, H-NMR spectrum (DMSO-d 6,TMS),δ (ppm): (d, 8H of aromatic ring), 6.85 (m, 2H of citraconimide), 2.10 (d, 6H, CH 3 of citraconimide). Elemental analysis calcd. for C 22 H 16 N 2 O 5 (388.37): C, 68.04; H, 4.15; N, Found: C, 68.32; H, 4.28; N, Biscitraconimide 1a The product was recrystallized from methanol, yield 83%, mp C. IR spectrum (KBr, cm 1 ): 3120, 2950, 2850, 1720, 1450, 1420, 1385, H-NMR spectrum (DMSO-d 6,TMS),δ (ppm): 6.35 (t, 2H of citraconimide ring), 3.35 (t,

5 148 C. Gaina and V. Gaina 4H, aliphatic protons N CH 2 ), 2.05 (d, 6H, CH 3 of citraconimide ring), 1.35 (m, 8H, aliphatic methylene protons). Elemental analysis calcd. for C 16 H 20 N 2 O 4 ( ): C, 63.15; H, 6.62; N, 9.2. Found: C, 63.56; H, 6.53: N, Biscitraconimide 1b The product was recrystallized from methanol, yield 85%, mp C. IR spectrum (KBr, cm 1 ): 3120, 1720, 1520, 1400, 1140, 1110, H-NMR spectrum (Clf, TMS), δ (ppm): 7.00 (s, 8H, aromatic ring), 6.20 (t, 2H of citraconimide ring), 3.90 (s, 2H, CH 2 from Ar CH 2 Ar), 2.10 (t, 6H, CH 3 of citraconimide ring) Biscitraconimide 1d The product was recrystallized from acetone, yield 82%, mp C. IR spectrum (KBr, cm 1 ): 3120, 1720, 1610, 1520, 1400, 1330, 1160, 1130, 875, 775, H-NMR spectrum (DMSO-d 6,TMS),δ (ppm): (m, 8H, aromatic protons), 6.90 (m, 2H, citraconimide ring), 2.10 (s, 6H, CH 3 of citraconimide ring). Elemental analysis for C 22 H 16 N 2 SO 6 ( ): C, 60.54; H, 3.69; N, 6.41; S, Found: C, 60.36; H, 3.83; N, 6.73; S, Synthesis of p-tolyl citraconimide 2 To a solution of 2.14 g (0.02 mol) p-toluidine in 50 ml glacial acetic acid 1.8 ml (0.02 mol) citraconanhydride was added and stirred at room temperature for 12 h. The reaction mixture was heated under reflux for 4 h and then concentrated under reduced pressure. Then, it was cooled and precipitated in 100 ml water. The solid formed was filtered and washed with 50 ml of 3% Na 2 CO 3 solution, then with water and dried at 80 C for 12 h in a vacuum oven. The yield after recrystallization from water was 2.8 g (86%), mp C (literature mp 115 C [18]). IR spectrum (KBr, cm 1 ): 3100, 2950, 1720, 1530, 1410, 1185, 1120, 1000, 895, 830, H- NMR spectrum (DMSO-d 6,TMS),δ (ppm): 7.10 (s, 4H, aromatic protons); 6.70 (d, 1H, CH C CH 3 ); 2.40 (s, 3H, CH 3 Ar); 2.10 (d, 3H, CH C CH 3 ) Synthesis of reaction model 3 To a solution of 1.61 g (8 mmol) p-tolyl citraconimide 2 in 30 ml acetone 0.5 ml (4 mmol) bis(1-mercapto-2-ethylether) was added with a syringe. The reaction mixture was stirred for 0.5 h at room temperature, at reflux for 2 h and then concentrated in vacuum up to 15 ml. This solution was precipitated in water and extracted with dichloromethane (2 30 ml). The combined extract was washed with water, dried (sodium sulfate), evaporated in vacuum to give 1.82 g (86.7%) of 3, as a yellow liquid. IR spectrum (KBr, cm 1 ): 2980, 2920, 2880, 1775, 1720, 1510, 1450, 1390, 1290, 1195, 1120, 950, 820, 760, 720, H-NMR spectrum (CHCl 3 -d 1,TMS),δ (ppm): 7.35 (d, 4H, J = 9 Hz, aromatic protons

6 Synthesis of new polyimidosulfides by Michael addition 149 ortho to N imide); 7.18 (d, 4H, J = 9 Hz, aromatic protons ortho to CH 3 ); 5.30 (s, 1H, to proton of 4-thio addition product, minor product); 3.70 (t, 4H of aliphatic protons CH 2 O CH 2 ); 3.05 (t, 4H of aliphatic protons CH 2 S); 2.70 (s, 3H of methylene protons of major products, addition of C 3 ); 2.40 (s, 6H of CH 3 Ar); 1.75 (s, 4H, CH 3 of geminal addition product); 1.50 (d, 2H, CH 3 of vicinal addition product). Elemental analysis calcd. for C 28 H 32 N 2 S 2 O 4 ( ): C, 64.10%; H, 6.14%; N, 5.34%; S, 12.22%. Found: C, 63.86%; H, 5.98%; N, 5.39%; S, 11.98% Synthesis of polymers 4a d A 100-ml three-necked flask equipped with magnetic stirrer, thermometer and condenser was charged with 2.97 g (77 mmol) biscitraconimide 1b and 10 ml freshly distilled NMP. Three drops of tributylamine were added and then 1 ml (77 mmol) bis(1-mercapto-2-ethylether) was added. The reaction mixture was heated at C for 6 h, then was cooled and precipitated in 100 ml methanol with 5 ml concentrated HCl. The product was washed with methanol and dried for 12 h in a vacuum oven at 60 C. The same synthesis system described above was used to prepare all polymers 4a d. 3. RESULTS AND DISCUSSION 3.1. Monomer synthesis N-p-Tolylcitraconimide and four biscitraconimides with primary amines or diamines, followed by cyclodehydration in situ of the biscitraconamic acids, by refluxing in the acetic acid (Scheme 1) were obtained. The structures of the biscitraconimides 1a d and N-p-tolylcitraconimide were confirmed by IR, 1 H-NMR spectroscopy and elemental analysis. The properties of the obtained monomers are listed in Table 1. The IR spectra of these monomers showed a characteristic carbonyl doublet bands in the range and cm 1. Other imide characteristic bands were observed in range 1400 cm 1 (imide II), cm 1 (imide III). All biscitraconimides gave a band at cm 1 due to the CH 3 from the imide ring. In addition, the IR spectrum of biscitraconimide 1c shows an adsorption band at 1270 cm 1 and 1d shows a strong absorption band at 1330 cm 1 ( SO 2 asymmetrical vibration) and at 1160 cm 1 ( SO 2 symmetrical vibration). The 1 H-NMR spectra of monomers 1a d showed the presence of aromatic, maleimide, citraconimide and methylene protons in the correct ratio for the expected structures. The cross-linking behavior of biscitraconimides 1a d was studied by differential scanning calorimetry (DSC), in nitrogen, at a heating rate of 10 C/min using the first heating cycle. Some of the DSC data are listed in Table 2 and presented in Figs 1 and 2. As can be seen, the DSC curves for the biscitraconimides were characterized by a sharp melting endotherm in the temperature range C, due to the melting of these monomers. All DSC curves exhibited an

7 150 C. Gaina and V. Gaina Table 1. Properties of monomers 1a d Monomer Yield (%) Melting point ( C) T m1 ( C) T onset ( C) T exo ( C) 1a b c d Melting points were determined with a Gallenkamp hot-block melting point apparatus. Endothermal peak temperatures, onset temperatures and exothermic peak temperatures were determined by DSC. Figure 1. DSC traces of biscitraconimides 1a d. exothermic transition associated to curing of the monomers in the range C. The rate of polymerization of biscitraconimides at a certain temperature is affected by the structure of the bridge units, as well as the substituted position. The onset temperature of curing reaction of these monomers increases in the order 1a 1c 1b 1d. Thus, the order of the reactivity increased via verso. The higher

8 Synthesis of new polyimidosulfides by Michael addition 151 Table 2. Elemental analysis of polymers 4a d Polymer Yield ηinh Mn 10 4 Mw/Mn Molecular formula/ C (%) H (%) N (%) S (%) (%) (dl/g) formula weight Calcd. Found Calcd. Found Calcd. Found Calcd. Found 4a C20H30N2S2O5/ b C27H28N2S2O5/ c C26H26N2S2O6/ d C26H26N2S3O9/ Number-average molecular weight and polydispersities were determined by GPC.

9 152 C. Gaina and V. Gaina Figure 2. DSC traces of polymers 4a d; run II. onset of curing of biscitraconimides 1d may be due to the high electron-withdrawing effect of the SO 2 group Polymer synthesis Chain extension of bismaleimides with bisthiols in order to give polyimidosulfides is well described in the literature [7 10] and linear or crosslinked polymers can be obtained. The synthesis of the polyimidosulfides by polyaddition reaction of bisthiols to biscitraconimides is not yet reported in literature. The addition of various alkyl mercaptans to citraconimides was presented [19]. The results indicate that the reaction of various mercaptanes with citraconimides is highly regioselective resulting in predominantely geminally substituted products. To facilitate the analysis of spectral data of polymers, a model compound 3 was prepared. By reaction of N-p-tolyl citraconimide 2 with bis(1-mercapto- 2-ethylether) in molar ratio 2 : 1 in the presence of tributylamine, a mixture of geminally (3e) and vicinally (3b or 3c) substituted products was prepared (Scheme 2). Products 3a c were isolated by extraction and the IR and 1 H-NMR spectra are presented in Figs 3 and 4. The IR spectra showed the absorption bands around 1400 and 1195 cm 1 corresponding to the vibration of the C N C linkages and due to the formation of succinimide ring by the polyaddition reaction. Other identified absorption bands were those at cm 1 corresponding to vibration of the C S C bond from polyimidosulfides.

10 Synthesis of new polyimidosulfides by Michael addition 153 Scheme 2. In 1 H-NMR spectra of crude products 3a c, the major product (geminally substituted product 3a) exhibited singlet for 3-methyl protons and the methylene protons for succinimide ring at 1.80 and 3.0 ppm, respectively. In comparison, 3-methyl protons from the minor products (i.e., the vicinally substituted products 3b or 3c) appeared as a doublet center at 1.50 ppm and the methylene protons from succinimide ring as two doublets at 3.15 and 3.85 ppm. The doublet of the 3-methyl protons in the minor product shows a splitting of 9 Hz. The ratio of geminallysubstituted product 3a and vicinally-substituted product 3b or 3c is 5 : 3bytheratio of the integrated signals for the 3-methyl protons of geminal and vicinal products. The poly(imidothioethers) 4a d were prepared by polyaddition of bis(2-mercaptoethylether) with biscitraconimides 1a d, in equimolecular ratio, in NMP that contains a catalytic amount of the tributylamine (TBA) (Scheme 3). The properties of the polymers are listed in Table 2. The structures of the polymers were confirmed by IR and 1 H-NMR spectroscopy and elemental analysis. Examination of IR spectra of all polyimidosulfides 4a d (Fig. 5) reveals that all spectra contain prominent characteristic bands of the succinimide and thioether groups. The weak absorption band at cm 1 and strong absorption band at cm 1 are characteristic of the succinimide carbonyl (C O) stretching frequencies. The presence

11 154 C. Gaina and V. Gaina Figure 3. IR spectra of monomer 2 and mixture model compound 3a, b, c. of absorption bands around 1400 and 1195 cm 1 corresponding to the vibration of C N C linkages are due to the formation of succinimide ring in the polyaddition reaction (Scheme 3). Other identified absorption bands of the polyimidosulfides are at 2950 and 2850 cm 1 (suggesting the presence of CH 2 linkages), and at cm 1, corresponding to the vibration of C S C links. The 1 H-NMR spectra of polymers confirmed their chemical structures. The 1 H-NMR spectrum of polymer 4b (Fig. 6) displays signals at ppm (q, aromatic protons), 4.10 ppm (s, 2H of CH 2 from Ar CH 2 Ar), ppm (t, 4H, CH 2 ether link from bisthiol and H of succinimide of vicinally substituted product), ppm (m, 8H, CH 2 protons of S CH 2 links and CH 2 from succinimide ring of geminally methyl substituted product), 2.10 ppm (d, 3H, CH 3 of citraconimide unreacted), 1.67 ppm (s, 3H, CH 3 of geminally substituted units) and ppm (d, 1H, CH 3 of vicinally substituted units). Data of elemental analysis of the polymers 4a d are listed in Table 2 and showed good agreement between calculated and found values. The polymers were obtained

12 Synthesis of new polyimidosulfides by Michael addition 155 Figure 4. 1 H-NMR spectra of monomer 2 and mixture model compound 3a, b, c. in 85 90% yields and their inherent viscosities ranged between 0.19 and 0.32 dl/g (Table 2). The GPC curves indicated that the M n values of polymers 4a d varied between and ,andM w /M n ratios, as a measure of the molecular weight distribution, were in range All polymers exhibited high solubility in aprotic dipolar solvents (DMF, NMP, DMSO). Flexible films for the polymers 4a d were obtained by casting from DMF solutions. Their thermal behavior was monitored by DSC and TGA measurements (Table 3). As can be seen, the polyimidosulfides 4a d showed an inflection curve in the second DSC run, corresponding to a glass temperature transition range between 78 and 157 C. The thermal stability of the polyimidosulfides was evaluated by dynamic TGA. All traces of the polymers 4a d showed two stages of decomposition. The first

13 156 C. Gaina and V. Gaina Figure 5. IR spectra of polymers 4a d.

14 Synthesis of new polyimidosulfides by Michael addition 157 Scheme 3. Figure 6. 1 H-NMR spectrum of polymer 4b. stage occurred between 295 and 323 C due to the decomposition of thioether aliphatic links and had 14 28% weight loss, corresponding to loss of hydrogen sulfide from the polymer [7]. The second stage of decomposition occurred between 450 and 472 C, depended upon the nature of the biscitraconimide structures and

15 158 C. Gaina and V. Gaina Table 3. Thermal properties of polymers 4a d Polymer T g ( C) IDT T 5 ( C) T 10 ( C) T 20 ( C) T 30 ( C) PDT max ( C)/ w (%) 4a /18; 450/40 4b /28; 472/23 4c /14; 458/20 4d /17; 452/19 IDT, initial decomposition temperature; T x, temperature for x% weight loss, PDT max,maximum decomposition temperature; w, weight loss at maximum decomposition temperature. was in accordance to maximum decomposition temperature of biscitraconimide monomers. The temperature for 10% weight loss was 276 C for polymer 4a and 338 C for polymer 4d, respectively. 4. CONCLUSIONS New polysulfides were prepared by addition reaction of bis(1-mercapto-2-ethylether) to biscitraconimides. The reaction of various mercaptanes with citraconimides is highly regioselective, resulting in predominantly geminally-substituted products. REFERENCES 1. J. V. Crivello, J. Polym. Sci. Polym. Chem. Edn. 11, 1185 (1973). 2. L. R. Dix, J. R. E. Ebdon, N. J. Flint, Ph. Hodge and R. O Dells, Eur. Polym. J. 31, 647 (1998). 3. C. S. Wang and T. S. Len, J. Appl. Polym. Sci. 73, 833 (1999). 4. M. F. Grenier-Loustalot and L. DaCuhna, Polymer 39, 1799 (1998). 5. W.Wu,D.WangandC.Ye,J. Appl. Polym. Sci. 70, 2471 (1998). 6. J. L. Hopwell, G. A. George and D. J. T. Hill, Polymer 41, 8221 (2000). 7. J. V. Crivello, J. Polym. Sci. Polym. Chem. Edn. 14, 159 (1976). 8. J. V. Crivello and P. C. Juliano, J. Polym. Sci. Polym. Chem. Edn. 13, 1819 (1975). 9. J. E. White, D. D. Snider and M. D. Scaia, J. Polym. Sci. Polym. Chem. Edn. 22, 589 (1984). 10. L. R. Dix, J. R. Ebdon and P. Hodge, Eur. Polym. J. 31, 653 (1995). 11. V. Taranu and S. Pecincu, Macromol. Rep. A31, 45 (1994). 12. V. Gaina, C. Gaina, C. Chiriac and M. Rusu, Macromol. Rep. A32, 121 (1995). 13. V. Gaina, C. Gaina, M. Sava, A. Stoleriu and M. Rusu, J. Macromol. Sci. Pure Appl. Chem. A34, 2435 (1997). 14. C. Gaina, V. Gaina, A. Stoleriu, M. Sava, C. Chiriac and V. Cozan, J. Macromol. Sci. Pure Appl. Chem. A34, 191 (1997). 15. V. Gaina, C. Gaina and M. Sava, Polym. Plast. Technol. Eng. 40, 89 (2001). 16. V. Gaina and C. Gaina, Polym. Plast. Technol. Eng. 43, 539 (2004). 17. G. B. Gill, G. D. James, K. V. Oates and G. Pattenden, J. Chem. Soc. Perkin Trans. 1, 2567 (1993). 18. D. Braun, W. Kczerwinski and R. Bednarschi, Makromol. Chem. 193, 477 (1992). 19. R. E. Earl, F. W. Clough and L. B. Townsend, Heterocycl. Chem. 15, 1479 (1973).