Nanofiltration membranes prepared by direct microemulsion copolymerizationusing poly(ethylene oxide) macromonomer as a polymerizable surfactant

A novel polymer membrane with nanosized pore structures has been prepared f rom the direct copolymerization of acrylonitrile (AN) with a polymerizable nonionic surfactant in water-in-oil (w/o) or bicontinuous microemulsions. T his polymerizable surfactant is omega-methoxy poly(ethylene oxide)(40) unde cyl-alpha-methacrylate macromonomer [CH3O-(CH2CH2O)(40)-(CH2)(11)-OCO(CH3)C =CH2, abbreviated: C-1-PEO-C-11-MA-40]. Besides PEO macromonomer, AN, and c rosslinker ethyleneglycol dimethacrylate, the microemulsion system containe d varying amount of water that formed w/o microemulsions having water dropl et structures and bicontinuous microemulsions consisting of interconnected water channel. The polymerized membranes prepared in this study have pore r adii ranging from 0.38 to 2.4 nm as evaluated by PEG filtration. The pore s ize appears to vary linearly with water content in precursor microemulsions . But a sharp change in the gradient of the linear relationship is observed around 25 wt % water content. Membranes made from bicontinuous (>25 wt % w ater) microemulsion polymerization have a larger and interconnected (open-c ell) nanostructures. In contrast, much smaller closed-cell (disinterconnect ed) nanostructures were obtained from w/o (<25 wt % water) microemulsion po lymerization and the membrane exhibited a permselectivity toward water in p ervaporation separation of high ethanol (>50 wt %) aqueous solutions. The s eparation factor (alpha) for 95% ethanol aqueous solution by the membrane d erived from the microemulsion containing 10 wt % water is about 20. (C) 200 0 John Wiley & Sons, Inc.