Synthesis, characterization and enzymatic degradation of novel biodegradable copolymers of 5-allyloxy-1,3-dioxan-2-one with ε-caprolactone

Abstract

Ring-opening copolymerization of 5-allyloxy-1,3-dioxan-2-one (ATMC) with ε-caprolactone (CL) was successfully performed for the first time in bulk at 140 °C using Sn(Oct)2 as the catalyst. Novel biodegradable copolymers with different compositions were characterized by 1H NMR, GPC, DSC, X-ray diffraction and static contact angle method. The copolymer composition was relevant to the monomer feed ratio, while the ATMC incorporation in the copolymers was less than that in the feed. With the increase of ATMC molar feed ratio from 25% to 75%, the Mn of the resulting copolymers decreased from 30,500 to 14,300 g/mol, while the static contact angle of the copolymers increased from 92.7° to 98.2°. The relationship between the copolymer glass transition temperature and composition was in agreement with the Fox equation. In vitro cytotoxicity studies using MTT assay demonstrated that the copolymer had low cytotoxicity compared to poly(ε-caprolactone) (PCL). Moreover, solution cast films were allowed to degrade in a pH 7.4 phosphate buffer solution containing Pseudomonas lipase. Weight loss data showed that the copolymers with ATMC content higher than 46% were not degradable and the enzymatic degradation rate increased with CL content. The areas of the diffraction peaks decreased gradually with increasing degradation time according to XRD analysis. Little changes of molecular weight can be detected during enzymatic degradation, in agreement with a surface erosion mechanism shown by SEM.