Unsymmetrical N-heterocyclic carbene: 1-isopropyl-3-benzylimidazol-2- ylidene as catalyst for ring-opening polymerization of ε-caprolactone

摘要

An unsymmetrical N-heterocyclic carbene, namely 1-isopropyl-3- benzylimidazol-2-ylidene, is a highly active catalyst for ring-opening polymerization of -caprolactone (CL) to give polycaprolactone (PCL) with number average molecular weight (Mn) as high as 2.66 10 ~4 at 0C in 100 min in tetrahydrofuran (THF). The effects of monomer/initiator molar ratio ([M]/[I]), catalyst/initiator molar ratio ([C]/[I]), monomer concentration, as well as polymerization temperature and time have been investigated. The kinetic studies of CL polymerization have indicated that the polymerization rate is first-order with respect to both monomer and catalyst concentrations. The apparent activation energy amounts to 56.04 kJ/mol. The proposed mechanism is a monomer-activated process.