Controlled synthesis of L-lactide-b-epsilon-caprolactone block copolymers using a rare earth complex as catalyst

Well-defined block copolymers of L-lactide-b-epsilon-caprolactone were synt hesized by sequential polymerization using a rare earth complex, Y(CF3COO)( 3)/Al(iso-Bu)(3), as catalyst system. The compositions of the block copolym ers could be adjusted by manipulating the feeding ratio of comonomers. The characterizations by GPC, H-1 NMR, C-13 NMR, and DSC displayed that the blo ck copolymer, poly(epsilon-caprolactone-b-L-lactide) [P(CL-b-LLA)], had a n arrow molecular weight distribution and well-controlled sequences without r andom placement.