To evaluate the effects of ionic liquids (ILs) on the microstructural features of aliphatic polyesters for biomedical applications, a series of copolymers were synthesized by lipase ring opening polymerization of rac-lactide (rac-LA) and ε-caprolactone (CL). The chemical structures of resulting polymers were characterized by ¹H- and 13C-NMR and the average molecular weight (Mn) and dispersity index were characterized by gel permeation chromatography. The structure of the copolymers confirms the presence of linear polymer chains with end-functional hydroxyl groups allowing covalent coupling of the therapeutic agents. Chain microstructure of copolymers indicates the presence of both random and block copolymers depending on the synthesis conditions. Moreover, it was found that CL is the most active co-monomer during copolymerization which enhances the polymerizability of rac-LA and allows to obtain higher Mn of the copolymers. The results demonstrate that ILs could be promising solvents in synthesis of aliphatic esters for biomedical applications.
Keywords: aliphatic polyesters; biomedical polymers; drug delivery systems; ionic liquids; lipases; polylactide; ring-opening polymerization; ε-caprolactone.