Novel Rare Earth Catalysts for the Living Polymerization and Block Copolymerization of ε-Caprolactone

Abstract

The steric effect of bulky groups of the catalyst can kinetically suppress the transesterification reactions by screening linear polymer chains from the active center during the polymerization of ε-caprolactone (CL) with rare earth alkoxide. Therefore, isopropoxy rare earth diethyl acetoacetate ((EA)2LnOiPr Ln = Nd, Y) and Nd(OiPr)3-donor adducts (1,10-phenanthroline, 2,2‘-bipyridyl, 18-crown-6 ether) are excellent catalysts for the living polymerization of ε-caprolactone, giving poly(ε-caprolactone) (PCL) with a narrow molecular weight distribution. Block copolymerizations of ε-caprolactone with trimethylene carbonate (TMC) and d,l-lactide (LA) have been attained successfully using (EA)2LnOiPr as catalyst. The characterizations by GPC, NMR, DSC, and polarizing microscope showed that the block copolymers, P(CL-b-TMC) and P(CL-b-d,l-lactide), have well-controlled sequences without random placement.