On-line version ISSN 0717-9707
J. Chil. Chem. Soc. vol.51 no.4 Concepción Dec. 2006
J. Chil. Chi. Soc., 51, N°.4 (2006), p.1041-1043
SYNTHESIS AND CHARACTERIZATION OF COMB-LIKE POLY(ESTERS) CONTAINING SILICON AND/OR GERMANIUM IN THE MAINCHAIN
L.H. TAGLE, C.A. TERRAZA, L. LÓPEZ AND A. LEIVA
Facultad de Química, Pontificia Universidad Católica de Chile, P.O. Box 306, Santiago, CHILE (email@example.com)
Poly(esters) derived from the acid dichloride bis(4-chloroformylphenyl)-n-octylmethyl-silane and the diphenols bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), bis(4-hydroxyphenyl)-dimethylsilane and germane were synthesized under phase transfer conditions and characterized only by IR spectroscopy due to the insolubility of the resulting polymers. The glass transition temperature and the thermal stability were determined showing that the Tg values decrease when the size of the central atom is increased. The thermal stability increased when the polarity of the main chain was increased in the poly(esters) containing the C-Si and the C-Ge bonds from the diphenol part, with respect to the analogous derived from bisphenol A.
Key words: poly(esters), silicon, germanium, glass transition temperature, thermal stability.
Silicon-containing polymers such as poly(amides), poly(esters), poly(imides) and others in which the Si atom is bonded to four organic groups, have been described by several authors [1-12]. In general, it has been described that the sililaromatic groups increase the solubility, but maintain a high thermal stability as a consequence of the ionic character of the Si-C bond, because the Si atom has higher electronegativity than the C one. On the other hand, the Tg values are lower due the longer Si-C bond in front of the C-C- one .
However, germanium-containing polymers, in which the Ge atom is bonded to four organic groups, have not received great importance, with the exception of our works with respect to the synthesis of poly(carbonates), poly(thiocarbonates), poly(esters), poly(amides) and poly(urethanes), several of them containing moreover the Si atom [13-20]. In those works we showed that the synthetic process does not display differences with respect to the nature of the heteroatom. The thermal properties were strongly influenced by the nature of the heteroatom and the organic groups bonded to them, although they showed good thermal properties and some of them were thermally stable.
Continuing our works describing the synthesis and thermal properties of condensation polymers containing Si and Ge in the main chain, in this work we describe the synthesis of comb-like poly(esters) derived from an aromatic acid dichloride with Si as central atom and bonded to a long aliphatic chain, and three diphenols: bisphenol A and the analogous with Si and Ge. As a polymerization method we used the phase transfer catalysis, which has been successfully used in the synthesis of several kinds of polymers .
Reagents and solvents (from Aldrich or Riedel de Haen) were used without purification. The IR spectra were recorded on a Perkin-Elmer 1310 spectrophotometer and the 1H, 13C and 29Si NMR on a 400 MHz instrument (Bruker AC-200), using acetone-d6 or DMSO-d6 as solvents and TMS as the internal standard.
Tg values were obtained with a Mettler-Toledo DSC 821 calorimetric system. Thermogravimetric analyses were carried out in a Mettler TA-3000 calorimetric system equiped with a TC-10A processor, and a TG-50 thermobalance with a Mettler MT5 microbalance. Samples of 6-10 mg were placed in a platinum sample holder and the thermogravimetric measurements were carried out between 30 and 800ºC with a heating rate of 20ºC min-1 under N-2 flow.
The acid dichloride and the diphenols were characterized by I.R. and 1H, 13C, and when it corresponded by 29Si NMR spectroscopy. Poly(esters) were characterized by I.R.
The acid dichloride bis(4-chloroformylphenyl)-n-octylmethyl-silane, was synthetized according to described procedures, in which the di(p-tolyl) derivative was oxidized to the corresponding diacid and then reacted with thionyl chloride [22-24].
Bis(4-methylphenyl)-n-octylmethyl-silane. B.p.: 121-124ºC/20 mm Hg. IR (KBr) (cm-1): 3032 (H arom.), 2956 (CH3), 2923, 2854 (CH2), 1603, 1501 (C=C arom.), 811 (arom. p-subst.). 1H NMR (acetone-d6) (d) (ppm): 0.61 (s,3H,CH3), 0.97 (t,3H,CH3), 1.09-1.42 (m,14H,CH2), 2.44 (s,6H,CH3), 7.34 (d,4H,arom.), 7.51 (d,4H,arom.). 13C NMR (acetone-d6) (d) (ppm): -4.42 (CH3-Si), 13.85 (CH3-CH2), 20.95 (CH3-arom.), 14.34, 22.52, 23.77, 29.11, 29.16, 31.77, 33.53 (CH2), 128.3, 133.5, 134.2, 137.9 (C arom.). 29Si NMR (acetone-d6) (d) (ppm): -7.86.
Bis(4-carboxyphenyl)-n-octylmethyl-silane. M.p.: 89-91ºC. IR (KBr) (cm-1): 3392 (OH), 3026 (H arom.), 2959 (CH3), 2924 (CH2), 1693 (C=O), 1599, 1501 (C=C arom.), 849 (arom. p-subst.). 1H NMR (DMSO-d6) (d) (ppm): 0.17 (s,3H,CH3), 0.5-1.53 (m,17H,CH3-(CH2)7-), 7.6 (d,4H,arom.), 7.91 (d,4H,arom), 13.21 (s,2H,OH). 13C NMR (DMSO-d6) (d) (ppm): -4.2 (CH3-Si), 14.1 (CH2-Si), 15 (CH3-CH2), 22.5, 23.4, 24.7, 29.8, 33.4, 34.1 (CH2) 129.6, 133.3, 134.1, 143.8 (C arom.), 168.7 (C=O). 29Si NMR (DMSO-d6) (d) (ppm): -6.5.
Bis(4-chloroformylphenyl)-n-octylmethyl-silane. B.p.: 70-72ºC/5 mm Hg. IR (KBr) (cm-1): 3026 (H arom.), 2956 (CH3), 2925 (CH2), 1776, 1739 (C=O), 1592, 1553 (C=C arom.), 862 (arom p-subst.). 1H NMR (acetone-d6) (d) (ppm): 0.71 (s,3H,CH3), 0.9-0.95 (t,3H,CH3-CH2) 1.2-1.47 (M,14H,CH2), 7.74 (d,4H,arom.), 8.13 (d,4H,arom.). 13C NMR (acetone-d6) (d) (ppm): -4.94 (CH3-Si), 13.43 (CH3-CH2), 14.17, 22.66, 23.6, 29.19, 31.6, 31.8, 33.56 (CH2), 146.2, 134.9, 128.9, 130.2 (C arom.), 168.5 (C=O). 29Si NMR (acetone-d6) (d) (ppm): -5.27.
The diphenols bis(4-hydroxyphenyl)-dimethyl-germane, and bis(4-hydroxyphenyl)-dimethyl-silane were synthesized from p-bromo-phenol and dimethyl-dichloro-germane, or dimethyl-dichloro-silane according to the procedure described by Davidson . Bis(p-hydroxyphenyl)-2,2-dimethylpropane (bisphenol A) was a commercial product.
Bis(4-hydroxyphenyl)-dimethyl-silane. M.p. 170-171ºC (Lit.  173-174ºC). IR (KBr) (cm-1): 3289 (OH), 3028 (H arom.), 2952 (CH3), 1601, 1503 (C=C arom.), 822 (arom. p-subst.). 1H NMR (d) (ppm) (acetone-d6): 0.45 (s,6H,CH3), 6.84 (d,4H,arom), 7.35 (d,4H,arom), 8.37 (s,2H,OH). 13C NMR (d) (ppm) (acetone-d6): -1.06 (CH3-Si); 116.6; 129.5; 137.1; 159.9 (C arom). 29Si NMR (acetone-d6) (d) (ppm): -6.1.
Bis(4-hydroxyphenyl)-dimethyl-germane. M.p. 160-161ºC (Lit.  161-163ºC). IR (KBr) (cm-1): 3291 (OH), 3024 (H arom.), 2971 (CH3), 1601, 1500 (C=C arom.), 820 (arom. p-subst.). 1H NMR (d) (ppm) (acetone-d6): 0.54 (s,6H,CH3), 6.84 (d,4H,arom), 7.30 (d,4H,arom), 8.31 (s,2H,OH). 13C NMR (d) (ppm) (acetone-d6): -2.34 (CH3-Ge); 116.8; 131.2; 136.3; 159.5 (C arom).
Poly(esters) were synthesized 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 20ºC. 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 40ºC until constant weight and characterized.
Poly(ester) I. IR (KBr) (cm-1): 3032 (H arom.), 2960 (CH3), 2924, 2854 (CH2), 1738 (C=O), 1599, 1505 (C=C arom.), 838 (arom. p-subst.).
Poly(ester) II. IR (KBr) (cm-1): 3025 (H arom.), 2960 (CH3), 2924, 2854 (CH2), 1739 (C=O), 1589, 1496 (C=C arom.), 835 (arom. p-subst.).
Poly(ester) III. IR (KBr) (cm-1): 3024 (H arom.), 2957 (CH3), 2924, 2854 (CH2), 1739 (C=O), 1587, 1493 (C=C arom.), 828 (arom. p-subst.).
RESULTS AND DISCUSSION
Poly(esters) derived from the acid dichloride bis(4-chloroformylphenyl)-n-octylmethyl-silane and the diphenols bis(p-hydroxyphenyl)-2,2-dimethyl-propane (bisphenol A) (PE-I), bis(4-hydroxyphenyl)-dimethyl-silane (PE-II) and bis(4-hydroxyphenyl)-dimethyl-germane (PE-III), were synthesized under phase transfer conditions in CH2Cl2 as solvent at 20ºC using two phase transfer catalysts. Poly(esters) were characterized by IR spectroscopy and elemental analysis, and the results were in agreement with the proposed structures.
In all polymers it was possible to see the disappearance of the OH band and to see a new band at 1738 cm-1 corresponding to the C=O of the ester group.
Poly(esters) were insoluble in all solvents. In fact, the solubility was intended in many solvents, common and uncommon, and it was only possible to see a swelling in toluene, but it was not possible to obtain a good quality NMR spectrum in toluene-d8. This lack of solubility can be due to the long aliphatic side chain which confers to the poly(esters) a very lypophilic character. In other polymers in which the Si or Ge atoms are bonded to two C4 chains, insolubility was also observed in all the solvents.
In this study the efficiency of the phase transfer process with the catalysts and without them, was studied by the yields obtained for each poly(ester). The catalyst concentration, solvent, reaction time and temperature remained constant. Three base concentrations were studied, with the molar ratios of NaOH/phenol 2/1, 3/1, and 4/1. 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 polymer, experiments without catalyst were made in order to evaluate the behaviour of the interphase of the system. In all cases polymers were obtained due to an interphasial polycondensation process between the diphenolate dissolved in the aqueous phase and the acid dichloride dissolved in the organic one.
When the catalysts were used it was possible to see only a very low increase of the yields due to the insolubility of the poly(esters) in the reaction media. However, the highest yields were obtained when a NaOH/phenol molar ratio of 3/1 was used, which can be due to a salting out effect of the diphenolate from the aqueous phase to the organic one. This effect has been described in other systems [16, 19, 26-27]. At higher NaOH concentrations it was possible to see in some cases, a decrease of the yields probably due to a hydrolysis of both, the acid dichloride or the polymeric chain. The main difficulty was the insolubility of the poly(ester) in the reaction media, which does not permit to obtain more accurate conclusions, caused by the long aliphatic side chains.
The thermal properties, Tg and thermal decomposition temperature (TDT) were determinedby differential scanning calorimetry and dynamic thermogravimetry respectively. Table II shows the values of the Tg for the three poly(esters).
The Ge atom is larger than Si, and the C-Ge bonds are longer than the C-Si ones, and therefore there will be lower rotational barriers in poly(esters) with the Ge atom. Consequently the poly(esters) with Si would show higher Tg values than the analogous with Ge, but lower than poly(ester) I in which the diphenol does not have any heteroatom, and showed the highest Tg value. The results are shown in Table II, the only difference in the poly(esters) being the central atom of the diphenol, and the results showed the above trend.
The thermal decomposition temperatures were taken when the poly(esters) lost 10% of weight. It has been described that the bond polarity increases the thermal stability of polymers and in this case poly(esters) derived from diphenols with Si or Ge, would have higher thermal stability than the analogous with carbon . In Table II it is possible to see that poly(esters) II and III with two heteroatoms in the main chain showed higher thermal stability than poly(ester) I only with one Si atom. The difference between poly(ester) II and III was low. Poly(ester) II with two Si atoms should have had a higher TDT value than poly(ester) III.
As a conclusion, poly(esters) with Si and/or Ge atoms in the main chain and a long side aliphatic chain, were obtained under phase transfer conditions, but were insoluble in all solvents, which caused low yields and probably low molecular weights. The Tg values were in agreement with the trend in the sense that those with larger atoms as Ge showed lower values. The TDT values increase when the polarity of the main chain is increased with respect to poly(ester) with only one Si atom.
The authors acknowledge the financial support of FONDECYT through grant 1030528.
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