Regulation of polar microenvironment on the surface of tertiary amines functionalized polyacrylonitrile fiber and its effect on catalytic activity in Knoevenagel condensation

Two fiber supported tertiary amine catalysts were prepared by immobilization of 3-dimethylamino-1-propylamine (PANDF) and 3-dimethylamino-N-methylpropylamine (PANTF) on polyacrylonitrile fiber. Both fiber catalysts contain polar microenvironments constructed by amide groups, tertiary amine groups and unreacted cyano groups. The difference between the two catalysts lies in that the PANDF contains hydrogen bond network while the PANTF does not. Employing Knoevenagel condensation as a model reaction, the cooperative action of immobilized tertiary amines with hydrogen bonds was evaluated in detail. At the same time, the aggregation of reactants in the polar microenvironment under different solvents was also investigated. The results showed that hydrogen bonds and the supporting basic groups can promote the reaction by the synergistic catalytic effect in most solvents. The catalysts displayed different catalytic behaviors in solvents with different polarities. The catalysts can achieve highly efficient catalytic activity in the more polar solvents which were well compatible with the catalysts. Moreover, the reaction can also occur in less polar solvents due to their incompatible property with the fiber catalysts, which can compel the polar reactants to accumulate on the fiber surface with strong polar microenvironment.