Synthesis of PEI Grafted Poly (Ionic Liquid)s: Optimization and Kinetics Modeling of Effective CO₂ Fixation Reactions

Fixing the greenhouse gas CO2 through epoxide helps to mitigate worldwide ecological troubles. The applications of metal-free and solvent-free catalysts remain a challenge for CO2 catalytic conversion. In this work, an array of quaternary ammonium salts derived from polyethyleneimine with hydroxyl groups ([PEI-GDMAB-C-n]Br) were constructed by the reaction of branched PEI with a molecular weight of 10000 and glycidyl alkyl dimethylammonium bromide. A range of experiments were designed to demonstrate that [PEI-GDMAB-C-n]Br can be considered as a valid metal-free and solvent-free homogeneous catalyst for the CO2-epoxide cycloaddition reaction. Among of [PEI-GDMAB-C-n]Br, [PEI-GDMAB-C-18]Br catalyzed the model reaction of CO2 and epichlorohydrin under optimized reaction conditions (T=80 degrees C, 1.0 atm CO2, catalyst 1 mol%, ECH 15 mmol, 16 h) and the conversion achieved at 97.5 %. Moreover, the catalyst exhibited stable reusability and broad substrate applicability, which was used in the following cycle succinctly, because of self-separated properties by temperature control. The [PEI-GDMAB-C-18]Br catalyzed reaction process was detected as a pseudo-first-order reaction after kinetic studies and an E-a was calculated to be 50.65 kJ/mol. A combinatorial catalytic mechanism of hydrogen bonding and bromide ions is suggested to explain the remarkable catalytic performance of this bifunctional catalyst.