SPONTANEOUS HYDROLYTIC DEGRADABILITY OF COPOLYESTERS HAVING TETRAHYDROPYRAN RINGS IN THEIR BACKBONES

Homo- and copolyesters, containing 2,5-linked tetrahydropyran rings in their backbones, were prepared by cationic ring-opening polymerizatio n of bicyclic lactones, 2,6-dioxabicyclo[2.2.2] octan-3-one (1), and i ts 4-methoxy-carbonyl and 4-benzyloxycarbonyl derivatives (3 and 4). C opolyesters, having pendant carboxyl groups, were derived from the cop olymers containing 4 as one of the comonomers by the catalytic hydroge nolysis of the pendant benzyloxy-carbonyl groups. Copolyesters, contai ning both 2,5-linked and 2,6-linked tetrahydropyran rings in the main chains, were obtained by the copolymerization of 1 with 6,8-dioxabicyc lo [3.2.1]octan-7-one (13), which is a structural isomer of 1. Spontan eous hydrolytic degradability of these polyesters was investigated in a phosphate buffer solution (pH 7.5) at 27-degrees-C. The degradabilit y of the polyesters markedly depended on the molecular structure: hydr ophobic pendant groups retarded the hydrolytic degradation, whereas hy drophilic pendant groups accelerated it. In particular, a small amount of pendant carboxyl groups significantly enhanced the hydrolytic degr adability of the copolyesters from 1. Polyesters, containing 2,6-linke d tetrahydropyran rings in their backbones, underwent hydrolytic degra dation more readily than those entirely consisting of 2,5-linked tetra hydropyran rings. (C) 1994 John Wiley & Sons, Inc.