Advanced ultrafiltration membranes based on functionalized poly(arylene ether sulfone) block copolymers

Abstract

In this study, poly(arylene ether sulfone) (PAES) block copolymer was synthesized from fluoride-terminated oligomer (A₁₆) and hydroxyl terminated oligomer (B₁₂) by aromatic nucleophilic substitution (S_NAr) polycondensation reaction. Then allylic free radical substitution reaction at methyl side group using N-bromosuccinimide and benzoyl peroxide was performed to synthesize PAES–CH₂Br block copolymer. The chemical structure of PAES and PAES–CH₂Br block copolymers was confirmed by ¹H-NMR spectroscopy. Gel permeation chromatography was applied to determine the molecular weight and the degree of polymerization of A₁₆ and B₁₂ oligomers, PAES and PAES–CH₂Br block copolymers. The synthesized block copolymer had high molecular weight and multiblock structure. Non-solvent induced phase separation of blends of PAES–CH₂Br and PAES block copolymers followed by heterogeneous quaternization using trimethyl amine led to hydrophilic positively charged ultrafiltration membranes. Fourier transform infrared spectroscopy in the attenuated total reflection mode, scanning electron microscopy, contact angle, and outer surface zeta potential studies were performed to characterize the resulting membranes. The results confirmed that the prepared membranes were porous, hydrophilic and positively charged. Membranes were also characterized with respect to permeability and then used in ultrafiltration of bovine serum albumin and lysozyme model solutions at varied pH values. Membrane performance depended on the positive charge density which could be adjusted by varying the fraction of PAES–CH₂Br in the membrane. Due to the combined effects of size exclusion and charge repulsion, permeability, antifouling properties and protein separation selectivity of membranes could be increased simultaneously with increasing charge density.