Benzo-12-crown-4 modifiedN-heterocyclic carbene for organocatalyst: Synthesis, characterization and degradation of block copolymers of ϵ-caprolactone withL-lactide

A set of poly(L-lactide)-poly(ϵ-caprolactone) diblock copolymers (AB) and poly(L-lactide)-poly(ϵ-caprolactone)-poly(L-lactide) triblock copolymers (ABA) with predictable molecular weights and relatively narrow distributions were synthesized by ring-opening polymerization of successively added ϵ-caprolactone (ϵ-CL) and L-lactide (LLA) using 4-methyl benzo-12-crown-4 imidazol-2-ylidene as catalyst. The effects of polymerization conditions, such as reaction time, temperature, monomer/catalyst molar ratio and monomer concentration on the copolymerization have been discussed in detail. The resulting copolymers were characterized by 1H-NMR, 13C-NMR, IR, GPC and DSC methods which confirmed the successful synthesis of block copolymers of LLA and ϵ-CL. Hydrolytic degradation of the polymers showed that the PLLA-PCL-PLLA copolymer exhibited faster degradation as compared with the PCL homopolymer in alkaline medium at 37°C.