| Abstract
| - Molecular modification of ozone-pretreated poly(vinylidene fluoride) (PVDF) via thermally induced graftcopolymerization with N-isopropylacrylamide (NIPAAM) in N-methyl-2-pyrrolidone solution was carriedout (the NIPAAM-g-PVDF copolymer). The chemical structure and composition of the NIPAAM-g-PVDFcopolymers were characterized by Fourier transform infrared spectroscopy, elemental analysis, andthermogravimetric analysis. In general, the graft concentration increased with the NIPAAM monomerconcentration used for graft copolymerization. Microfiltration membranes were prepared from the NIPAAM-g-PVDF copolymers by the phase inversion method. The bulk and surface graft concentrations of themembranes were obtained by elemental analysis and X-ray photoelectron spectroscopy (XPS), respectively.XPS analyses of the copolymer membranes revealed a substantial surface enrichment of the grafted NIPAAMpolymer. The pore sizes of the pristine PVDF and the NIPAAM-g-PVDF membranes were measured usinga Coulter Porometer. The morphology of the membranes was studied by scanning electron microscopy. Themembrane surface composition, mean pore size, and morphology varied with the temperature of the castingbath. For the copolymer membrane cast below the lower critical solution temperature (LCST) of the NIPAAMpolymer (∼32 °C), the rate of water permeation increased substantially at a permeate temperature above32 °C. A reverse permeate temperature dependence was observed for the flux of 2-propanol through themembrane cast above the LCST of the NIPAAM polymer.
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