Experimental and Theoretical Studies on the Polymerization of Isobutylene Using the GaCl3-Based Catalytic System

This work investigates a novel GaCl3·AlCl3/H2O catalytic system for the synthesis of low-molecular weight polyisobutylene (LPIB). Catalytic performance was improved by employing a dual Lewis acid system, which outperformed the conventional single component (GaCl3/H2O) catalyst in terms of both reaction rate and yield. In accordance with the optimized reaction conditions, the conversion of monomer was found to be 97%, thereby achieving low molecular weight polyisobutylene (LPIB) with a number average molecular weight (Mn) of 3900 g/mol. Density functional theory (DFT) calculations revealed a lower proton transfer barrier (5.8 kcal/mol) in the dual Lewis acid catalytic structure compared to its single component counterpart. Subsequent theoretical analyses, incorporating electrostatic potential (ESP), independent gradient model based on Hirshfeld partition (IGMH), and distortion/interaction analysis, attributed this observed kinetic advantage to a higher positive ESP extremum and enhanced interaction between the IB fragment and the Lewis-acidic active center. Together, these results establish the GaCl3·AlCl3/H2O dual Lewis acid system as an enhanced catalytic platform over the conventional GaCl3/H2O system for efficient IB polymerization toward LPIB synthesis.