Ring-opening polymerization of lactones using zirconocene catalytic systems: Block copolymerization with methyl methacrylate

The ring-opening polymerization of epsilon-caprolactone (epsilon-CL) and delta-valerolactone (delta-VL) using nine catalytic systems consisting of a combination of three C-2v zirconocene complexes and three borate cocatalysts is discussed. The polymerizations proceed in a well-controlled manner, producing polymers with relatively high molecular weights and narrow molecular weight distributions. Kinetic experiments of the polymerization of epsilon-CL with the catalytic system Cp2ZrMe2/B(C6F5)(3) (1) showed a linear dependence between polymerization yield and molecular weight with time, as well as between the molecular weight with the molar ratio of the monomer over the catalyst [epsilon-CL]/[Zr], indicating sufficient control of the polymerization reaction. The catalytic system (1) was utilized for the synthesis of well-defined block copolymers of MMA with epsilon-CL and delta-VL. All samples were characterized by size exclusion chromatography, nuclear magnetic resonance, and differential scanning calorimetry. (C) 2007 Wiley Periodicals, Inc.