Effect of nucleophiles on isobutylene carbocationic polymerization

Isobutylene(IB) cationic polymerization by DiCumCl/TiCl4 was studied, and the effects of nucleophiles on PIB growing end were analyzed by UV spectroscopy. Using molecular simulation, the activation energy for reaction of nucleophiles with H+ was calculated by Molecular orbital package(MOPAC) method in semi-experiential quantum dynamics, and the change value of carbonic atoms of the growing species of isobutylene reacting with N-containing nucleophile reagent was obtained by QEq method after conformation optimization by using molecular dynamics. It was found that nucleophiles can complex with protons and so prevent chain transfer and chain termination reactions related with protons, and can also stabilize carbocations by reducing their charges. There are different reaction abilities between nucleophiles and protons or carbocations. Piperidine and 2, 6-diter-butyl pyridine are strong nucleophiles which may complex with protons. 2, 6-Diter-butyl pyridine can only trap protons and cannot complex with carbocations because of its big molecular volume. Piperidine is a good proton trap agent that can complex with carbocations to reduce their charge and increase their stabilization.