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Journal of the Chilean Chemical Society

On-line version ISSN 0717-9707

J. Chil. Chem. Soc. vol.50 no.3 Concepción Sept. 2005

http://dx.doi.org/10.4067/S0717-97072005000300002 

 

J. Chil. Chem. Soc., 50, N° 3 (2005), págs: 535-539

 

SYNTHESIS OF CONDENSATION POLYMERS DERIVED FROM SILYLATED MONOMERS UNDER PHASE TRANSFER CATALYSIS

 

L.H. TAGLE*, C.A. TERRAZA, W. AHLERS, and C. VERA

Facultad de Química, Pontificia Universidad Católica de Chile P.O. Box 306, Santiago, CHILE e-mail: ltagle@puc.cl


SUMMARY

The synthesis of the poly(carbonate) and poly(thiocarbonate) derived from the diphenol bis(4-hydroxyphenyl)-phenylmethylsilane and the poly(ester) derived from the same diphenol and the acid dichloride bis(4-chloroformylphenyl)-phenylmethylsilane are described. Polymers were synthesized under phase transfer conditions and the results were evaluated by the yields and inherent viscosity values. The phase transfer process was effective, but the results were affected by the increase of the NaOH concentration in the aqueous phase, in the sense that it was possible to see hydrolytic processes that decrease the yields and the inherent viscosity values. Also there was an influence of the nature of the catalysts, with BTEAC being efficient due to it hydrophilic nature.


INTRODUCTION

Since the first silicon-containing polymer was synthesized [1] an important number of condensation polymers containing the Si-atom bonded to four carbon atoms such as poly(esters), poly(amides), poly(imides) and others, have been synthesized and their properties described [2]. In this sense these kinds of polymers have been of great interest since they have potential applications in optoelectronic materials [3-4]. Also aromatic silane functions have been incorporated into thermally stable polymers with the objective of improving their processing characteristics [5].

However, we have not found poly(carbonates) and poly(thiocarbonates) derived from diphenols in which the Si-atom is bonded to two different groups, aromatic and aliphatic. Only poly(esters) and poly(amides) have been described from the diacids bis(4-carboxyphenyl)-diphenylsilane and bis(4-carboxyphenyl)-dimethylsilane [6-7]. On the other hand, the poly(carbonate) derived from a diphenol in which the Si-atom is bonded to two methyl groups has been described and the thermal and the photooxidative behaviour studied [8]. Neither have we found references with respect to the synthesis of poly(esters) derived from a diacid and a diphenol containing both a Si-atom bonded to a methyl and phenyl groups.

In the last years we have described the synthesis of several kinds of condensation polymers derived from diphenols containing Si and/or Ge in the main chain [9], and using the phase transfer catalysis as the polymerization method. We have focussed our attention on the influence of the nature of the catalyst and the concentration of NaOH in the aqueous phase. In this sense, when this concentration is increased, it is possible to see a salting out effect of the diphenolate to the organic phase, which has as a consequence an increase of the yields and hinh values. Also the increase of the NaOH concentration can hydrolyze the substrate and the polymeric chains and as a consequence, obtain lower yields and hinh values. The first situation was observed in the synthesis of poly(esters) and poly(thiocarbonates) [10-11] and the second with poly(carbonates) [11], which was attributed to the hydrolysis of the phosgene and the poly(carbonate) chains in the organic phase. Also the catalysts have influence in these hydrolytic processes according to their structure.

Continuing our works in the synthesis of condensation polymers derived from monomers, diphenols or acid dichlorides, containing Si in the main chain, in this work we described the synthesis of the poly(carbonate) and poly(thiocarbonate) derived from the diphenol bis(4-hydroxyphenyl)-phenylmethylsilane, and the poly(ester) derived from the same diphenol and the acid dichloride bis(4-chloroformylphenyl)-phenylmethylsilane. As the polymerization technique we used phase transfer catalysis, in which the diphenolate is transferred as an ionic pair with the catalyst, from the aqueous phase to the organic one, in which the reaction takes place. The qualitative behaviour of the catalysts and the NaOH concentration was evaluated by the yields and inherent viscosity values.

EXPERIMENTAL PART

Reagents and solvents (from Aldrich or Riedel de Haen) were used without purification. The following catalysts (from Fluka) were used: tetrabutylammonium bromide (TBAB), benzyltriethylammonium chloride (BTEAC) and methyltrioctylammonium chloride (ALIQUAT 336TM).

The IR spectra were recorded on a Perkin-Elmer 1310 spectrophotometer and the 1H, 13C and 29Si NMR on a 400 MHz Bruker instrument, using CDCl3, DMSO-d6 or acetone-d6 as solvents and TMS as the internal standard. Viscosimetric measurements were made with a Desreux - Bischoff [12] type dilution viscosimeter at 25°C.

Monomers

Bis(4-hydroxyphenyl)-phenylmethylsilane was synthetized according to the procedure described by Davidson [13], in which 7.1 g (0.041 mol) of p-bromophenol in THF were added under N2 to 60 mL of n-butyllithium (1.6 N solution in n-hexane) at ­70C. Then, the temperature was increased slowly up to 5C and the mixture stirred for one hour. The temperature was decreased to ­50C and 0.013 mol of phenylmethyldichlorosilane were added in THF, and the temperature was increased up to 10C and stirred for 2 hours. The mixture was hydrolyzed by adding 5% HCl until a yellow solution (pH = 1) was obtained. The organic layer was dried under MgSO4 and the solvent evaporated. The brown oil was poured in n-hexane obtaining a white solid which was recrystallized from toluene and characterized.

M.p.: 119-123C. IR (KBr) (cm-1): 3315 (OH), 3021 (H arom.), 2953 (CH3), 1600, 1584, 1504 (C=C), 830 (arom. p-subst.), 731, 699 (arom. mono-subst.). 1H NMR (acetone-d6) (d) (ppm): 0.81 (s,3H,CH3), 6.92 (d,4H,arom.), 7.42-7.68 (m,9H,arom.), 8.72 (s,2H,OH). 13C NMR (acetone-d6) (d) (ppm): -3.68 (Si-CH3), 116.1, 128.8, 129.2, 130.4, 135.1, 136.8, 140.5, 160 (arom.). 29Si NMR (acetone-d6) (d) (ppm): -11.96.

Bis(p-tolyl)-phenylmethylsilane was synthetized according to the following procedure [14] described previously in which 1.5 mL of p-bromotoluene (0.012 mol) in 5 mL of dry ether were added under N2 flow to a 0.18 g of Li and the mixture refluxed for 4 hours. When the Li reacted, 0.006 mol of phenylmethyldichlorosilane in 5 mL of dry ether, were added drop by drop and refluxed for 3 hours. The mixture was hydrolyzed with 30 mL of 5% HCl solution. The organic layer was separated, washed several times with water and dried with MgSO4. The solvent was evaporated and the solid recrystallized.

M.p.: 81-82C. IR (KBr) (cm-1): 3047 (H arom.), 2955, 2919 (CH3), 1597, 1499 (C=C), 803 (arom. p-subst.), 738, 701 (arom. mono-subst.). 1H NMR (acetone-d6) (d) (ppm): 0.88 (s,3H,CH3), 2.40 (s,6H,CH3), 7.15 (d,4H,arom.), 7.36-7.59 (m,9H,arom). 13C NMR (acetone-d6) (d) (ppm): -2.92 (Si-CH3), 21.9 (CH3), 129.1, 129.9, 130.6, 133.8, 136.3, 136.4, 137.9, 140.4 (arom.). 29Si NMR (acetone-d6) (d) (ppm): -11.04.

The bis(p-tolyl)-phenylmethylsilane was oxidized to the bis(4-carboxyphenyl)-phenylmethylsilane according to the following procedure [15]: 1 g (3.31 mmol) of bis(p-tolyl)-phenylmethylsilane was suspended in a mixture of 50 mL of glacial acetic acid, 17 mL of acetic anhydride and 2 mL of concentrated sulfuric acid. Then 3.2 g of chromic acid were added over 55 minutes at 15C. The reaction mixture was stirred for 10 minutes and poured in ice and stirred for 30 minutes. The solid diacid was filtered, washed and dried. The crude diacid was dissolved in NaHCO3 and reprecipitated with diluted HCl. The pure diacid was filtered, washed with water, dried under vacuum and characterized.

M.p.: 114-118C (decomp.). IR (KBr) (cm-1): 3431 (OH), 3024 (H arom.), 2903 (CH3), 1693 (C=O), 1599, 1499 (C=C), 851 (arom. p-subst.), 758, 700 (arom. mono-subst.). 1H NMR (DMSO-d6) (d) (ppm): 0.87 (s,3H,CH3), 7.34-7.39 (m,5H,arom.), 7.54 (d,4H,arom.), 7.90 (d,4H,arom). 13C NMR (DMSO-d6) (d) (ppm): -4.3 (Si-CH3), 127.9, 128.3, 129.7, 131.3, 133.8, 134.4, 134.7, 141 (arom.), 167.6 (C=O). 29Si NMR (DMSO-d6) (d) (ppm): -10.5.

The acid dichloride bis(4-chloroformyl-phenyl)-phenylmethylsilane was synthetized according to the general procedure: 1 g of the diacid was mixed with 30 mL of thionyl chloride and a drop of N,N-dimethyl-formamide and the mixture refluxed for 5 hours. The excess of thionyl chloride was destiled and 10 mL of petroleum ether were added obtaining a yellow solid which was recrystallized in benzene obtaining a white solid, which was characterized.

M.p.: 73-76C. IR (KBr) (cm-1): 3047 (H arom.), 2961 (CH3), 1780, 1736 (C=O), 1590, 1489 (C=C), 837 (arom. p-subst.), 736, 708 (arom. mono-subst.). 1H NMR (acetone-d6) (d) (ppm): 0.95 (s,3H,CH3), 7.45-7.56 (m,5H,arom.), 7.88 (d,4H,arom.), 8.21 (d,4H,arom.). 13C NMR (acetone-d6) (d) (ppm): -4. 6 (Si-CH3), 129.7, 131.5, 134.6, 135.2, 135.6, 136.4, 137.6, 146.5 (arom.), 169.2 (C=O). 29Si NMR (DMSO-d6) (d) (ppm): -10.56.

Poly(ester) synthesis

The poly(ester) was synthetized according to the following general procedure: 1 mmol of the diphenol was dissolved in 0.5M NaOH and water (total volume 15 mL), and the catalyst (5% in mol) was added. To this solution 1 mmol of the acid dichloride in 15 mL of CH2Cl2 was added and the mixture stirred for one hour at 20C. After this time the mixture was poured into 350 mL of methanol. The poly(ester) was filtered, washed with methanol and dried under vacuum at 40C until constant weight and characterized.

IR (KBr) (cm-1): 3022 (H arom.), 2956 (CH3), 1738 (C=O), 1580, 1496 (C=C), 830 (arom.p-subst.), 736, 699 (arom. mono-subst.). 1H NMR (CDCl3) (d) (ppm): 0.88 (s,3H,CH3), 0.95 (s,3H,CH3), 7.23-8.22 (m,26H,arom.). 13C NMR (CDCl3) (d) (ppm): -3.6 (Si-CH3), -3.12 (Si-CH3), 121.3, 128, 128.1, 128.3, 128.9, 129.4, 129.7, 130.2, 130.4, 134.1, 135.3, 135.5, 135.8, 136.7, 137 (C arom.), 152.2 (C-O), 165.2 (C=O). 29Si NMR (CDCl3) (d) (ppm): -10.55, -10.58.

Poly(carbonate) and poly(thiocarbonate) synthesis

The poly(carbonate) and poly(thiocarbonate) were synthesized according to the following general procedure: the diphenol (1 mmol) was dissolved in 0.5 M NaOH and water (total volume 15 mL), and 15 mL of CH2Cl2 and the catalyst (5% in mol) were added. To this mixture 1 mmol of phosgene (from a toluene solution) or thiophosgene was added and the mixture stirred at 20C for one hour. After this time the organic layer was poured into 300 mL of methanol and the polymer was filtered, washed with methanol, dried until constant weight, and characterized.

Poly(carbonate). IR (KBr) (cm-1): 3022 (H arom.), 2958 (CH3), 1775 (C=O), 1589, 1497 (C=C), 813 (arom. p-subst.), 730, 700 (arom. mono-subst.). 1H NMR (CDCl3) (d) (ppm): 0.87 (s,3H,CH3), 7.29-7.69 (m,13H,arom.). 13C NMR (CDCl3) (d) (ppm): -3.20 (Si-CH3), 120.5, 128.1, 129.8, 130.1, 134, 135.2, 135.5, 136.7 (arom.), 152.2 (C=O). 29Si NMR (CDCl3) (d) (ppm): -10.58.

Poly(thiocarbonate). IR (KBr) (cm-1): 3022 (H arom.), 2956 (CH3), 1585, 1494 (C=C), 1185 (C=S), 812 (arom.p-subst), 727, 700 (arom. mono-subst.). 1H NMR (CDCl3) (d) (ppm): 0.89 (s,3H,CH3), 7.22-7.62 (m,13H,arom.). 13C NMR (CDCl3) (d) (ppm): -3.19 (Si-CH3), 121.4, 128.1, 129.8, 134, 134.5, 135.3, 136.7, 157.7 (arom.), 193.9 (C=S). 29Si NMR (CDCl3) (d) (ppm): -10.52.

RESULTS AND DISCUSSION

The poly(carbonate) (I) and the poly(thiocarbonate) (II) derived from the diphenol bis(4-hydroxyphenyl)-phenylmethylsilane with phosgene or thiophosgene respectively, were synthesized under phase transfer conditions in CH2Cl2 as solvent at 20C using several phase transfer catalysts. The poly(ester) (III) was synthesized from the acid dichloride bis(4-chloroformylphenyl)-phenylmethylsilane and the diphenol bis(4-hydroxyphenyl)-phenylmethylsilane under phase transfer conditions in CH2Cl2 as solvent at 20C using the same phase transfer catalysts. Polymers were characterized by IR and 1H, 13C and 29Si NMR, and the spectral data were in according to the proposed structures.

In all polymers it was possible to see the disappearance of the OH band. In the poly(carbonate) it was possible to see a new band at 1775 cm-1 corresponding to the C=O of the carbonate group, and in the poly(thiocarbonate) there was an increase of the band at 1185 cm-1 corresponding to the C=S group. In the poly(esters) it was possible to see a new band at 1738 cm-1 corresponding to the C=O of the ester groups.

In this study the efficiency of the phase transfer process with each catalyst and without it, was studied by measuring the yields and inherent viscosity (hinh) values of the obtained polymers. The catalyst concentration, solvent, reaction time and temperature remained constant. Three base concentrations were studied, the molar ratios of NaOH/phenol being 3/1, 4/1, and 6/1. The volume of the aqueous phase was the same in all cases (15 mL).

The reaction takes place when the diphenolate dissolved in the aqueous phase is transferred to the organic one in the form of an ionic-pair with the catalyst. For all the polymers experiments without catalyst were made in order to evaluate the behaviour of the interphase of the system. In all cases the polymers were obtained due to an interphasial polycondensation process between the diphenolate dissolved in the aqueous phase and the phosgene, thiophosgene or acid dichloride dissolved in the organic one.

Table I shows the yields and hinh values obtained for the poly(carbonate) I and poly(thiocarbonate) II.


For the poly(carbonate) the use of the catalysts only showed a low increase of the yields, but with similar values of hinh. The increase of the NaOH concentration implied a decrease of the yields in all the essays and also in some cases of the hinh values due to a hydrolytic process of the phosgene which decreases the yields as well as of the polymeric chains which decreases the viscosity. The hydrolytic process is higher in those essays in which the more lypophilic catalysts were used, TBAB and Aliquat, and the poly(carbonate) was not obtained at the highest NaOH concentration [16]. The inverse can be observed with BTEAC, which is a hydrophilic catalyst and consequently not appropriate for the transfer of OH- anions, and in this case the hydrolysis is less important.

On the other hand the low increase of the hinh without catalyst and at the highest NaOH concentration, can be due to a salting out effect of the diphenolate from the aqueous phase to the organic one, which has been describe in other systems [9-10].

The fact that in some essays the values of hinh are lower than those obtained without catalyst, would be indicative that the polymerization is more influenced by the transfer process which depends on the catalyst, instead the reaction in the organic phase. Also there is a hydrolytic process, which affects the substrate in the interphase and the polymeric chains in the organic phase, this being dependant on the nature of the catalyst.

For the poly(thiocarbonate) at the same conditions the phase transfer process was more effective, in the sense that practically in all cases the yields were relatively high. However, the increase of the yields was not important, only BTEAC showing a low increase. This catalyst is described as hydrophilic [17] and consequently useful for the transporting of a diphenolate with a high organic content. When the NaOH concentration was increased there was no important decrease of the studied parameters. With TBAB there was a low increase probably as a conse

quence of a salting out effect of the diphenolate from the aqueous phase to the organic one. Apparently both thiophosgene and the poly(thiocarbonate) would be more stable in the hydrolytic process even at high NaOH concentrations. A similar behaviour has been described in other systems with Si or Ge in the main chain [11,18-19]. With these very similar values, it is not possible to obtain more conclusions.

Table II shows the yields and hinh values obtained for the poly(ester) III at the same conditions. Without catalyst, polymers were obtained by an interphasial polycondensation process, between the diphenolate dissolved in the aqueous phase and the acid dichloride dissolved in the organic one. The phase transfer process did not show important effectiveness because there were no important changes in the results when the catalysts were used compared with the essays without them. When the highest NaOH concentration was used, there was a decrease of the yields as a consequence of the hydrolysis of both the acid dichloride and the poly(ester). The exception was BTEAC, a hydrolytic catalyst which is not appropriate for transporting this diphenol with high organic content. The decrease of the parameters at the highest NaOH concentration was low because it does not promote the hydrolytic process.


Low yields were described in the synthesis of poly(carbonates) and poly(thiocarbonates) derived from diphenols containing Si or Ge bonded to two ­CH3 or -C6H5 groups [16], but when poly(esters) derived from the same diphenols were synthesized using a NaOH concentration higher than the stoichiometric, there was an important increase of the yields and hinh due to a salting out effect of the diphenolate from the aqueous phase to the organic one [13]. In this work we used a NaOH concentration which was twice the stoichiometric, and probably there was a salting out that increased both parameters, the yields and the hinh values.

With BTEAC and Aliquat we also obtained lower yields and hinh values. BTEAC is normally partitioned mainly in the aqueous phase due to the hydrophilic character [17], and Aliquat mainly in the organic phase due to the more lypophilic character of this catalyst due to the three C8 chains bonded to the N atom.

In spite of the low yields and hinh obtained for these polymers, it is possible to see an increase of these parameters when the catalysts were used in comparison with the essays without catalysts.

ACKNOWLEDGEMENTS

The authors acknowledge the financial support of FONDECYT through grant 1030528.

 

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