Synthesis, characterization and degradation of poly(silyl ester)s
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To investigate the effects of sterics and polymer backbone composition upon the rates of hydrolytic degradation of polymers containing trialkyl-substituted silyl ester linkages, six poly(silyl ester)s with molecular weights typically ranging from 5000 to 15000 Da were synthesized through transsilylation ester exchange reactions of alkyl or aryl bis(trimethylsilyl)esters with methyl- and isopropyl-substituted bis(chlorosilyl)hexanes to give trimethylsilyl chloride as the condensate. Characterization of the poly-(silyl ester)s included infrared spectroscopy (IR), 1H NMR, 13C NMR, and 29Si NMR INEPT spectroscopies, size-exclusion chromatography (SEC), differential scanning calorimetry, and thermogravimetric analysis. Both 29Si NMR and SEC were employed to monitor the polymerization and the degradation experiments. As expected, the relative stability of the silyl ester bonds toward hydrolysis increased with increased steric hindrance of the substituents attached to the silicon atoms. The incorporation of p-phenylene groups into the polymer backbone allowed for the formation of crystalline domains, which in turn greatly increased the stability toward hydrolytic degradation of the polymers in the solid state. Hydrolysis of the polymers containing diisopropyl-substituted silyl esters gave small molecules; however, degradation of the dimethyl-substituted poly(silyl ester)s as solids in air resulted in the formation of poly(dimethylsilylhexylene siloxane) from the spontaneous condensation of 1,6-bis(dimethylhydroxysilyl)hexane.
author list (cited authors)
Wang, M., Weinberg, J. M., & Wooley, K. L.
complete list of authors
Wang, M||Weinberg, JM||Wooley, KL