Effect of chain architecture and comonomer ratio on the biodegradability and thermal stability of biodegradable copolymers of l-lactide and δ-valerolactone

Abstract

A series of novel biodegradable homopolymers and copolymers of L-lactide (LA) and δ-valerolactone (VL) were polymerized at 165 °C using stannous octoate as a catalyst initiated with salicylic acid or benzyl alcohol via ring-expansion or ring-opening polymerization, respectively. The polymer chain topology was suggested to be either cyclic or linear depending on the initiator used. The feeding molar ratio of LA : VL was changed to investigate the chain microstructure, thermal properties, as well as degradability of copolymers. ¹H-NMR revealed that incorporating 30, 50, and 70 mol% VL provided blocky, gradient, and random chain copolymers, respectively. Increasing VL content relative to the LA content decreased the T_g, T_m, and crystallinity of the copolymers. All copolymers displayed higher thermal stability than PLA homopolymers due to the presence of the VL comonomer. The cyclic polymers showed higher T_g, lower T_m, and lower crystallinity than their linear counterparts. Furthermore, it was found that the degradability of the copolymers can be controlled by adjusting the compositions of VL and LA and their chain architecture.