Synthesis and in vitro degradation of poly(L-lactide-block-glycidol)

Abstract

Block copolymers of L-lactide (LLA) and glycidol (G) were synthesized by ring-opening polymerization of LLA using tin octoate [Sn(Oct)2] and branched polyglycidol (PG) as an initiation system. The molecular weight of the block copolymers depend on the reaction temperature, reaction time, and monomer feed ratio (LLA:G). Results from GPC chromatograms suggested that different polymeric species including homo PLLA might occur during the polymerization. At high LLA:G feed ratio (10:1) two types of polymeric products having different solubilities in methanol were obtained. It was found that the methanol-insoluble portion having higher molecular weight than the methanol-soluble portion. The suitable polymerization condition was carried out without solvent at 130°C for 24 hours. The amount of Sn(Oct)2 was 5%mol of the total hydroxyl group content in PG. The glass transition temperatures (Tg) of the block copolymers were found to be between those of PG and PLLA and increased with increasing the copolymer molecular weight. The block copolymer was more hydrophilic than homo PLLA and increased with decreasing LLA content as examined by air-water contact angle measurement. The obtained block copolymer degraded in phosphate buffer saline at pH 7.4 at a slower rate than the homo PLLA having the same molecular weight. The weight loss of the copolymer was however slightly more than that of homo PLLA, probably due to dissolution of the cleaved water-soluble PG block.