SYNTHESIS OF DEGRADABLE POLYESTERS HAVING PENDANT ESTER GROUPS BY RING-OPENING POLYMERIZATION OF 4-SUBSTITUTED 2,6-DIOXABICYCLO[2.2.2]OCTAN-3-ONE DERIVATIVES

New polyesters (8-10) containing tetrahydropyran rings in their backbone chains and ester groups in the side chains were synthesized by cationic ring-opening polymerization of 4-substituted 2,6-dioxabicyclo[2.2.2]octan-3-one derivatives (5-7) by using boron trifluoride etherate as an initiator in dichloromethane at -60-degrees-C. The polyesters 8-10 having number average molecular weights up to 3.8 x 10(4) were soluble in a variety of solvents including benzene, tetrahydrofuran, acetone, and dimethyl sulfoxide in which the parent polyester (2) without pendant ester groups was insoluble. The polyesters 8 and 9 containing hydrophilic oxyethylene moieties in the side chains swelled in methanol, and 9 swelled even in water. Thin films of these polyesters underwent spontaneous hydrolysis in a neutral phosphate buffer solution (pH 7.5) at 30-degrees-C. The apparent rate of the heterogeneous hydrolysis was markedly dependent upon the hydrophilicity of the polyesters, increasing in the order of 10 < 4 almost-equal-to 2 < 8 < 9.