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

The ring-opening polymerization of ε-caprolactone (ε-CL) and δ-valerolactone (δ-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 ε-CL with the catalytic system Cp₂ZrMe₂/B(C ₆F₅)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 [e-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 ε-CL and δ-VL. All samples were characterized by size exclusion chroma-tography, nuclear magnetic resonance, and differential scanning calorimetry.