Influence of the Chemical Structure of Terminal Groups on the Properties of Poly(phenylene sulfone) Ultrafiltration Membranes

Abstract

For the first time, poly(phenylene sulfones) (PPSFs) with chlorine and hydroxyl terminal groups are synthesized and tested for casting high-performance flat-sheet ultrafiltration membranes. The synthesis of PPSFs is carried out in dimethylacetamide at various ratios of 4,4'-dihydroxydiphenyl and 4,4-dichlorodiphenyl sulfone monomers. Two samples with the predominant content of hydroxyl (PPSF-ОН) and chlorine (PPSF-Cl) terminal groups are studied by NMR spectroscopy, GPC, and DSC methods. The coagulation values of polymer solutions in N-methyl-2-pyrrolidone (NMP) and the mechanical properties and hydrophilicity of polymer materials are determined. Both PPSF samples exhibit high tensile strength values at a level of 16 MPa. Using the method of precipitation of PPSF solutions in NMP with PEG-400 additives into water flat-sheet porous asymmetric membranes with a mesoporous (a pore diameter of about 7 nm) thin outer layer and fingerlike macropores in the substrate layer are obtained. An increase in the proportion of hydroxyl terminal groups enhances the hydrophilicity of the polymer. This, in turn, allows for the preparation of flat-sheet membranes from PPSF-ОН with a water permeability of 66 L/(m² h bar), which is 1.5 times higher than the water permeability of the PPSF-Cl membrane. Meanwhile, both membranes demonstrate a Blue Dextran (M_w = 70 000 g mol^–1) rejection of 99.9%.