pH-responsive permeability of PE-g-PMAA membranes

Poly(methacrylic acid) (PMAA) grafted porous PE membranes (PE-g-PMAA) were studied. It was found that (1) a wide range of graft yields can be achieved by varying irradiation time (20-240 min) and monomer concentration (0.22M-0.66M), (2) the grafted membrane exhibits reversible permeability response, (3) the membrane shows a maximum permeability response at an intermediate permeant molecular weight due to size exclusion effect, and (4) depending on the graft yield, two types of permeability response can be obtained. These observations are consistent with our earlier study on poly(N-isopropylacrylamide) (PNIPAAm)-grafted porous polyethylene membranes. In addition, it was observed that the solvent used during grafting may influence the graft location-presumably due to variations in pore wetting. Specifically, compared to water solvent, methanol can increase grafting inside membrane pores, an observation inferred from membrane swelling, thickness measurement, and SEM characterization. Moreover, preferential grafting inside the membrane pores, as affected by increasing methanol content in the grafting solvent, results in lower membrane permeability and a greater pore graft-controlled type of permeability response. (C) 2000 John Wiley & Sons, Inc.