Structure and catalytic performance relationship of ionic liquids as recyclable alcoholysis catalysts for green preparation of ethylene-vinyl alcohol copolymer

Alcoholysis is an important reaction for the current industrial production of ethylene-vinyl alcohol (EVOH) copolymers. Herein, two series of ionic liquids (ILs), acidic and basic ones, were used as eco-friendly catalysts for alcoholysis of ethylene-vinyl acetate (EVA) copolymer. The effects of the reaction parameters (catalyst loading, n(CH3OH)/n(Ac) and reaction time), EVA composition, and nitrogen flow on the alcoholysis were systematically investigated. A nearly 100% of alcoholysis degree was achieved using acidic ILs ([BHSO(3)MIm][HSO4]) under the optimum conditions (3.0 mol% catalyst loading relative to the VA units in EVA, n(CH3OH)/n(Ac) = 30, 70 degrees C, 6 h). Moreover, [BHSO(3)MIm][HSO4] could be reused at least five times without the decrease of catalytic activity, showing excellent recyclability. The interactions between IL and the substrate methanol and the model compound ethyl acetate were investigated by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance techniques, and on the basis of these results, the plausible mechanisms of acidic and basic ILs catalyzed alcoholysis of EVA were proposed.