Copolymer of lactide and ε-caprolactone catalyzed by bimetallic Schiff base aluminum complexes

A series of copolymers of lactide（LA） and e-caprolactone（ε-CL） with different monomer feed ratios were achieved using three kinds of bimetallic Schiff aluminum complexes as catalysts. The ratios of LA and ε-CL units in different copolymers and the average segments length were determined by NMR analysis. The comparative kinetic study of L-LA/ε-CL and rac-LA/ε-CL copolymerization systems showed that the polymerization rate of LA was faster than ε-CL, and L-LA showed polymerization rate slightly faster than rac-LA. It was inferred that the copolymers achieved by these complexes were gradient copolymers with gradual change in distribution of LA and e-CL units. The thermal properties of these copolymers were characterized by DSC analysis, which showed that the glass transition temperature（Tg） of these copolymers changed regularly according to the pro-portion change of two structural units.