Cationic polymerization of isobutylene by AlCl3 in polar solvents at mild temperatures

In the present study, adiabatic cationic polymerizations of isobutylene catalyzed by aluminum chloride were performed in different polar solvents (dichloromethane, dichloroethane and their mixtures with n-hexane), temperatures (10 °C and 30 °C) and concentrations of co-catalysts (water and dibutyl ether, DBE) to evaluate the respective impacts on the microstructure of the produced poly (isobutylene) (PIB). Reactions performed at 30 °C were characterized by quick heat release, fast polymerization kinetics and production of PIB samples with low average molar masses (<1300 Da), high polydispersities (4.57) and up to 25.7 mol% of vinyl content (conventional PIB, CPIB). On the other hand, reactions performed at 10 °C and with higher concentration of DBE provided highly reactive PIB (HRPIB) (vinyl content of 71.8 mol%) with low average molar masses (around 1600 Da) and lower polydispersity (3.68). Empirical mathematical modeling showed that temperature and DBE concentration exerted the most significant influences on vinyl content and molar mass, suggesting that these parameters can be used to modulate β-H elimination in the cationic polymerization of PIB towards the synthesis of conventional or HRPIB at non cryogenic temperatures.