Density functional theoretical studies on the ring-opening polymerization mechanism of oxetane cation series compounds†
The mechanism of ring-opening polymerization of oxetane cation series compounds was investigated using the B3LYP and MP2 methods of density functional theory and ab initio methods, at the basis set levels of 6-31G(d,p) and 6-311++G(d,p). The geometrical parameters of the reactant, transition state, intermediate and product of a series of multi-polymer species in the reaction pathway were fully optimized. The structural changes of species in the reaction pathway are explained herein. The computing results show that the polymerization of oxetane is performed by the O atom of oxetane continuously attacking the C atom of the oxetane cation. The energy analysis of the reaction process shows that the acidized oxetane can easily polymerize with other oxetane molecules to form a copolymer, and the activation energy in the initial step is very low. The equilibrium and transition state characteristics of every stationary point in the reaction pathway were determined through vibrational analysis. The corresponding reactant and product of each transition state were verified according to the intrinsic reaction coordinates traced from the transition state of different hierarchical polymers. Finally, the solvent effects of tetrahydrofuran and dichloromethane are discussed herein based on the self-consistent reaction field theory.