Study on cationic polymerization of isobutylene using electrochemical method

The cationic polymerization of isobutylene (IB) initiated by H₂O/TiCl₄ was carried out in a mixture of methylene dichloride and n-hexane at −60 °C in the presence of a variety of external electron pair donors (EDs), such as triethylamine (TEA), N,N-dimethyl acetamide (DMA) and pyridine (Py). The effects of ED concentration ([ED]), H₂O concentration ([H₂O]) on conductance and capacitance in H₂O/TiCl₄/ED/CH₂Cl₂ reaction system were investigated. The effects of [ED], [H₂O], solven polarity and polymerization time on monomer conversion, molecular weight (MW), molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) were also investigated. Conductance decreased while capacitance increased with increases in both [ED] and electron donicity of ED. Conductance and capacitance increased with [H₂O] when [H₂O] was more than [Py]. Both unpaired and paired ions existed as propagating species or chain carriers in the presence of relatively low [ED] and polymers with bimodal molecular weight distribution (peak a and b) were obtained. The peak a with high molecular weight was induced by propagation via unpaired ions while peak b with low molecular weight was induced by propagation via paired ions. The propagation via paired ions could be achieved and polymers with unimodal molecular weight distribution could be produced when sufficient amounts of external ED was introduced to polymerization system.