A theoretical study of the mechanism of cationic polymerization of isobutylene catalysed by EtAlCl/-BuCl with bis(2-chloroethyl)ether in hexanes.

The mechanism of cationic polymerization of isobutylene catalyzed by -BuCl/ethylaluminum dichloride (EADC) combined with bis(2-chloroethyl)ether (CEE) in -hexane solvent has been investigated using molecular dynamics (AIMD) and metadynamics (MTD) simulations. The results indicated that the polyisobutylene (PIB) initiation stage involves a clear two-step mechanism. Calculation of the free energy landscapes of the other two ether reactions reveals that the energy barriers of diisopropyl ether (i-PrO) and 2-chloroethyl ethyl ether (CEEE) are much higher than those of CEE, which is consistent with the experimental results. During the chain propagation phase, the required free energy barrier gradually decreases and tends to reach equilibrium as the chain length increases. Finally, the oxonium mechanism during the chain initiation stage was investigated by calculating the H NMR spectra and MTD simulation. Our calculations can confirm that the existence of -butyloxonium ions during the reaction is possible. Their contribution to the whole reaction is further discussed.