A ruthenium-catalyzed hydrosilane-induced polymerization of 3-alkyl-3-hydroxymethyloxetane derivatives: Facile access to functionalized polyoxetanes by virtue of organosilyl groups

Ring-opening polymerization of 3-alkyl-3-alkoxymethyl- or 3-alkyl-3-siloxymethyloxetanes is catalyzed by a triruthenium cluster, [Ru ₃{μ₃-(η₂,η₃, η₅-C₁₂H₈)}(CO)₇], in the presence of trialkylsilanes, providing a novel accessible method for functionalized polyoxetanes of M_n = 10₃-10₅. Oxetanes having alkoxy-, fluoroalkoxy-, triethyleneglycoloxy-, and trialkylsiloxy functions undergo polymerization and copolymerization. Consumption rates of two monomers in the copolymerization of 3-benzyloxymethyl- and 3-trimethylsiloxymethyl-3-alkyloxetanes are almost the same, indicating formation of random copolymers. The organosilyl group in the polymer and copolymers with siloxymethyl side chains is converted to CH₃OH or CH₂OCOR groups by hydrolysis or silyl/acyl exchange. These protocols give the way to access polymers or copolymers bearing OH and OCOR side chains. A ruthenium-catalyzed reaction of 3-ethyl-3- hydroxymethyloxetane with trialkylsilanes results in dehydrogenative silylation to give 3-ethyl-3-siloxymethyloxetane, which is followed by ring-opening polymerization. Combination of tandem dehydrogenative silylation/ring-opening polymerization/the silyl/acyl exchange realizes one-pot synthesis of polymers with CH₂OCOR side chains from 3-ethyl- 3-hydroxymethyloxetane. DSC analyses of the formed polymers provided T_g and T_m data, which are a good example showing that the polymer properties are controlled by appropriate selection of functional groups at the side chain.