AbstractHomo‐ and copolyesters, containing 2,5‐linked tetrahydropyran rings in their backbones, were prepared by cationic ring‐opening polymerization of bicyclic lactones, 2,6‐dioxabicyclo 2.2.2 octan‐3‐one (1), and its 4‐methoxy‐carbonyl and 4‐methoxy‐carbonyl and 4‐benzyloxycarbonyl derivatives (3and4). Copolyesters, having pendant carboxyl groups, were derived from the copolymers containing4as one of the comonomers by the catalytic hydrogenolysis of the pendant benzyloxy–carbonyl groups. Copolyesters, containing both 2,5‐linked and 2,6‐linked tetrahydropyran rings in the main chains, were obtained by the copolymerization of1with 6,8‐dioxabicyclo 3.2.1 octan‐7‐one (13), which is a structural isomer of1. Spontaneous hydrolytic degradability of these polyesters was investigated in a phosphate buffer solution (pH 7.5) at 27°C. The degradability of the polyesters markedly depended on the molecular structure: hydrophobic pendant groups retarded the hydrolytic degradation, whereas hydrophilic pendant groups accelerated it. In particular, a small amount of pendant carboxyl groups significantly enhanced the hydrolytic degradability of the copolyesters from1. Polyesters, containing 2,6‐linked tetrahydropyran rings in their backbones, underwent hydrolytic degradation more readily than those entirely consisting of 2,5‐linked tetrahydropy
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