Acrylonitrile-based copolymers containing reactive groups: synthesis and preparation of ultrafiltration membranes

Copolymerization of acrylonitrile (AN) and maleic anhydride was conducted by a water-phase precipitation copolymerization process (WPPCP) with K2S2O8-Na2SO3 as initiator system and the resultant copolymers were used to fabricate ultrafiltration hollow fiber membranes (UHFMs) by a dry-wet phase inversion method. Structures and properties for the UHFMs were studied by the analysis of scanning electron microscopy and the measurements of water permeation, bovine serum albumin (BSA) rejection and breaking strength. Compared with normal solution copolymerization, only poly(acrylonitrile-co-maleic acid)s (PANCMAs) could be obtained with WPPCP due to the hydrolysis of maleic anhydride, however, advantages of WPPCP including high monomer conversion and high copolymer molecular weight were obtained. It was found that increasing the molecular weight of PANCMA or the concentration of casting solution raised BSA rejection and mechanical strength but decreased water flux for the corresponding UHFMs. Membrane structures and properties could also be adjusted by adding additives such as poly(vinyl pyrrolidone) and poly(vinyl alcohol) (PVA) to the casting solution. Ternary phase diagrams of the membrane-forming systems and viscosity data of the casting solutions were used to characterize the characteristics of thermodynamics and diffusion kinetics for the membrane-forming systems. Most promisingly, it was found that the acid groups on membrane surface of PANCMA could be conveniently converted to more reactive anhydride groups by treating the membranes with acetic anhydride/pyridine mixture. Finally, the potentiality for the immobilization of poly(ethylene glycol) (PEG) on membrane surface by the reaction of PEG with anhydride groups to further improve the membrane properties was briefly indicated using Fourier-transform infrared spectroscopy (FT-IR), pure water contact angle and BSA adsorption measurements combining water permeation and BSA rejection determinations. (C) 2003 Elsevier B.V. All rights reserved.