Ring-opening copolymerization of L-lactide with ε-caprolactone initiated by diphenylzinc

Copolymerization of mixtures of L-lactide and e-caprolactone has been initiated by diphenylzinc. The reaction conditions were investigated, to discover the effects on yield, molecular weight and microstructure of copolymers obtained. The temperature used varied between 50 and 120 degrees C, the molar ratio of monomer to initiator ranged between 90 and 1440 mol/mol, and the molar ratio of epsilon-caprolactone to L-lactide employed was between 100/0 and 0/100mol/mol. Copolymers were characterized by H-1-NMR, C-13-NMR, DSC and gel permeation chromatography. The results indicate that incorporation of L-lactide to the growing chain is preferred and epsilon-caprolactone is copolymerized after most of the L-lactide has been depleted. The microstructure of obtained copolyesters was affected considerably by transesterification reactions. It was observed that increasing reaction temperature, reaction time and concentration initiator was advantageous to the transesterification. The crystallinity of copolyester obtained was determined by differential scanning calorimetry. The results are in good agreement with both molar composition and sequence distribution of copolyesters. (C) 2006 Society of Chemical Industry.