Synthesis and Characterization of Degradable Poly(silyl ester)s

Abstract

Polymers containing labile silyl ester bonds along the backbone were synthesized via a transsilylation ester interchange reaction. The condensation of the bis(trimethylsilyl) esters of adipic acid and sebacic acid with several bis(silyl chloride)s gave trimethylsilyl chloride as the condensate and formed the new silyl ester bonds composing the polymer backbones. Alteration of the degradation properties of the poly(silyl ester)s was demonstrated with the synthesis of nine polymers consisting of three series with variation in the silicon side chain substituents, the backbone composition adjacent to the silicon atoms, or the backbone composition adjacent to the carbonyl moieties. Characterization of the poly(silyl ester)s included infrared spectroscopy, 1H, 13C, and 29Si NMR spectroscopies, size exclusion chromatography (SEC) (typical molecular weights ranged from 2000 to 10 000), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The degradative properties of the polymers were evaluated by 29Si NMR, and molecular weight loss was evaluated by GPC. Increased steric bulk and decreased electronegativity of the substituents attached to the silicon atoms resulted in decreased monomer reactivity and increased degradation times for the polymers. Hydrolysis of the polymers in solution gave small molecules while condensation of the disilanol degradation products occurred in the solid-state degradations to give polysiloxanes.