Porous Membranes of Polysulfone-graft-poly(tert-butyl acrylate)and Poly sulfone-graft-poly( acrylic acid): Morphology,pH-Gated Water Flow,Size Selectivity,and Ion Selectivity

摘要

Membranes were prepared from two samples of polysulfone-graft-poly(tert-butyl acrylate),PSf-g-PtBA,by immersion into water of solution films of the polymers first solvated in l-methyl-2-pyrrolidinone (MP)and propionic acid (PA).Polysulfone-graft-poly(aery lie acid),PSf-g-PAA,membranes were obtained after soaking the PSf-g-PtBA membranes in trifluoroacetic and formic acid to hydrolyze PtBA.Both PSf-g-PtBA and PSf-g-PAA membranes had high water permeability.An electron microscopic study revealed that the membranes were porous and asymmetric.In the skin layer,the polymer formed a nodular phase consisting of fused polymer lumps surrounded by void channels.The PAA chains and presumably also the PtEA chains were concentrated at the lump/lump or lump/void interfaces.At a constant pressure,the water flux across PSf-g-PAA membranes decreased with increasing solution pH probably due to the extension of the PAA chains into the channels at high pH.The PSf-g-PAA membranes also showed permselectivity toward anions of lower valence and may be used to separate NaCl from Na2SO4,for example.A permeation test using poly(ethylene glycol)samples of different molar masses showed that membranes of a PSf-g-PAA sample had a size of-2 nm at constrictions of the nanochannels.