Polyether-Functionalized Comb-Shaped Alkali Ionic Liquid Polymers for Knoevenagel Condensations

Comb-shaped ionic liquid polymers P[VB(EG)_nIm][OH] (n = 0, 2, 3, 4) with varying polymerization degrees of polyether groups were successfully synthesized and characterized by FTIR, NMR, and ESI-MS. The Knoevenagel condensation reaction was selected as a model reaction to evaluate their catalytic performances. The influence of the polymerization degree of polyether groups on catalytic activity was studied. The results indicated that higher catalytic activity was obtained with increasing polymerization degree, owing to the enhancement of surface activity and the high local center activity concentration of the ionic liquid polymers. Among these ionic liquid polymers, P[VB(EG)₄Im][OH] exhibited the best catalytic performance owing to the OH anion, higher surface activity, and easy formation of hydrogen bonds with active centers. Using P[VB(EG)₄Im][OH] as the catalyst, the influence of solvent types on the catalysis effect was investigated. When dimethyl sulfoxide was used as the solvent, 97.6% yield was achieved because of its higher polarity and higher compatibility with reactants.