Polymer Brush Membranes for Pervaporation of Organic Solvents from Water

Atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate from initiators immobilized on porous supports yields high-flux pervaporation membranes that can be readily modified to control their properties. Derivatization of poly(2-hydroxyethyl methacrylate) (PHEMA) coatings with octyl (C8-PHEMA), hexadecyl (C16-PHEMA), or pentadecafluorooctyl (fluorinated PHEMA) side chains provides films that are sufficiently hydrophobic to allow selective pervaporation of volatile organic compounds (VOCs) from water. For all of these derivatized PHEMA membranes, VOC/water selectivities generally increase with decreasing solubility of the VOC in water, and trichloroethylene/water selectivities are about 500. Sorption data suggest that fluorinated PHEMA has the highest free volume and that C16-PHEMA has the lowest, and consistent with this inference, fluxes decrease in the order fluorinated PHEMA > C8-PHEMA > C16-PHEMA. The ATRP and derivatization reactions readily yield defect-free films with thicknesses <200 nm, and this minimal thickness results in fluxes of ∼1.4 kg/(m 2 h) (0.05 wt % VOCs at 22 °C) through fluorinated films. These fluxes are generally an order of magnitude greater than those through high-performance poly(dimethylsiloxane) pervaporation membranes. The use of different monomers or derivatization reagents may further enhance the flux and selectivity of pervaporation membranes prepared by ATRP.