Charged ultrafiltration membranes of polyacrylonitrile covalently binding amphiphilic quaternary ammonium group: effect of aliphatic hydrophobic groups on the filtration properties

Amphiphilic monomers of chloromethylstyrene derivative were synthesized and then copolymerized with acrylonitrile for the preparation of positively charged ultrafiltration membranes. Four types of the polyacrylonitrile charged membranes having quaternary ammonium group with trimethyl, dimethylbutyl, dimethyloctyl and dimethylstearyl groups were prepared by the phase-inversion method. The ultrafiltration properties of the charged membranes were measured by using dextran molecular probes at various NaCl concentrations. Then, the filtration behavior was compared in these charged membranes. For membranes with trimethyl and dimethylbutyl groups on the quaternary ammonium salt, the values of the molecular weight cutoff and the permeation rate of the solute solution increased when the salt concentration increased. However, for membranes having amphiphilic quaternary ammonium groups with octyl and stearyl aliphatic chains, the filtration properties did not change with the salt concentration. We concluded that a compact conformation of the amphiphilic polyionic segments in the membrane causes stable filtration properties.