Study on anionic polymerization of ethylene oxide initiated by ammonium/triisobutylaluminum

In this paper, ammonium/triisobutylaluminum was used as an initiating system for anionic polymerization of ethylene oxide (EO). When the amount of triisobutylaluminum versus ammonium was in excess, a fast polymerization rate was achieved at room temperature and allowed polyethylene glycol synthesized with a high molecular weight and narrow molecular weight distribution. It was found that triisobutylaluminum may play two roles during the polymerization, one is that it can react with ammonium to form "ate" complex as an efficient initiator for EO polymerization, and the other is that it exerts a significant activating effect on the monomer. The catalytic effect of triisobutylaluminum in EO polymerization was elucidated by using quantum chemical calculations at density functional theory level, involving thermo-chemistry parameters. The studies show that EO homopolymerization cannot be conducted without the aid of catalyst due to the big energy difference of bonding orbitals. The interaction between EO and trialkylaluminum makes the electron cloud distribution and energy gap of EO molecule change, which indicates trialkylaluminum can activate the monomer. In addition, because of the lower enthalpy of formation, the formation of "ate" complex is prior to the interaction of trialkylaluminum and EO.