Ring-opening polymerization by N-heterocyclic carbenes as catalysts: Characteristics and kinetics

In this work catalytic ring-opening polymerization of cyclic esters in THF in the presence of benzyl alcohol is described. The polymerization is catalyzed by 1,3- bis (4-methoxyphenyl)imidazolium carbene, N-heterocyclic carbene (NHC). The ability of two different monomers, ɛ-caprolactone and L-lactide, to enter into the polymerization via ring-opening polymerization with NHCs as catalysts was evaluated. The plot of ln([M] 0 /[M] t ) versus reaction time yielded a straight line indicating that the kinetics of polymerization of ɛ-caprolactone and L -lactide was first-order in monomer concentration. Moreover, a direct relation between the rate of ring-opening polymerization of ɛ-caprolactone and the catalyst concentration suggested a first-order dependence of the rate of polymerization on the catalyst concentration.