A Study on the Initiation Mechanism of Uncatalyzed Polymerization by the Frontier Electron MO Method

Abstract

In the uncatalyzed polymerization, it was realized that the initiation reaction took place through a hydrogen transfer, as shown in Scheme 1 (in Text). The radicals [1] and [2] were caught by the spin-trapping method. In order to support the mechanism, perturbation energies, ΔE, of the hydrogen transfer reaction between acrylonitrile (AN) and the complexes of AN with Lewis base were calculated by Frontier Electron MO method. As the models of the macromolecular anion or Lewis base, HCOO-:, CH₃COO-: and (CH₃)₂O: were applied. The calculations were carried out by the ab initio Hartree-Fock (STO-3 G basisset)method. ΔE of the hydrogen atom transfer reaction from AN to AN, from HCOO: … AN to AN, from CH₃COO:… mAN to AN, and from (CH₃)₂O:… AN to AN were 0.003, 0.030, 0.029 and 0.029 eV, respectively. By complexing of AN with Lewis base, the energy levels of MOs of AN raise. Accordingly, the σ-HOMO of the complex becomes to go near to the π*-LUMO of the free AN. And tIE becomes thus larger and the hydrogen transfer from the complexed AN to a free AN may proceed.