Synthesis and characterization of a functionalized biodegradable copolymer: poly(l-lactide-co-RS-β-malic acid)

The ring-opening copolymerization of l-lactide (l-LA) and RS-β-benzyl malate (MA) was performed in the presence of stannous octoate. Copolymers were successfully synthesized using different feeding doses. 1H NMR analysis revealed that the compositions of the copolymers with high MA contents were similar to the feeding doses. GPC measurements showed that the molecular weight of the copolymers decreased as the MA content increased. The hydrophilicity of these copolymers was remarkably improved after they were hydrogenolyzed over palladium on charcoal, which removed the pendant benzyl groups. These de-protected copolymers had higher glass transition temperatures (Tg) than both the corresponding protected copolymers and the PLLA homopolymer due to the formation of intermolecular hydrogen bonds between the pendant carboxyl groups. The morphology of the copolymers changed from crystalline to amorphous with increasing RS-β-malic acid content.