Synthesis and characterization of fluorinated polyimide with grafted poly(N-isopropylacrylamide) side chains and the temperature-sensitive microfiltration membranes

Abstract

Molecular modification of a fluorinated polyimide (FPI), 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride + 4,4′-bis(4-aminophenoxy)diphenyl sulfone, via ozone pretreatment and thermally induced graft copolymerization with N-isopropylacrylamide (NIPAAm) in a N-methyl-2-pyrrolidone solution, was carried out. The resulting FPIs with grafted NIPAAm polymer side chains [FPI-g-P(NIPAAm) copolymers] were cast into microfiltration membranes by phase inversion in water at temperatures ranging from 4 to 55°C. The surface composition of the membranes was characterized by X-ray photoelectron spectroscopy. The surface composition, mean pore size, and morphology of the membrane varied with the temperature of the aqueous coagulation bath. For the copolymer membrane cast below the lower critical solution temperature of the NIPAAm polymer (∼32°C), the rate of water permeation increased substantially at a permeate temperature above 32°C. For the flux of 2-propanol through the membrane cast above 32°C, a reversed permeate temperature dependence was observed.