Flash Communication: Temperature-Dependent Initiation Mechanism in AlCl ₃ -Catalyzed Cationic Polymerization of Isobutylene

The monomeric AlCl3–H2O species is commonly accepted as the initiating species in the AlCl3-catalyzed cationic polymerization of isobutylene. However, density functional theory (DFT) calculations reveal that the dominant initiating species during the initiation stage are the dimeric AlCl3 complexes A0 (Al2Cl6–H2O) and C0 (Al2Cl5OH- -HCl), rather than B0 (AlCl3HOHAlCl3) as proposed by Johnson et al. (ACS Catal. 2018, 8, 8006). Herein, we propose a novel temperature-dependent initiation mechanism for the AlCl3-catalyzed cationic polymerization of isobutylene: initiation by a small amount of C0 at low temperature, and co-initiation involving both A0 and C0 at room temperature.