Functional poly(vinylidene fluoride) copolymer membranes via surface-initiated thiol-ene click reactions

Thermally induced graft copolymerization of allyl methacrylate (AMA) from ozone-preactivated poly (vinylidene fluoride) (PVDF) chains was first carried out in N-methyl-2-pyrrolidone (NMP) solution to produce the PVDF-g-PAMA copolymers. The PVDF-g-PAMA copolymers were cast, by phase inversion in an aqueous medium, into microporous membranes with enriched allyl groups on the membrane and pore surfaces. The pendant allyl groups in the PAMA side chains allowed the thiol-ene click grafting of thiol-functionalized moieties on the membrane surface. Thermally initiated thiol-ene click reaction with 3-mercaptopropionic acid (MPA) produced the PVDF-g-P[AMA-comb-MPA] membrane which exhibited a pH-responsive permeation behavior, with the most drastic change in permeation rate of the aqueous media being observed between pH 2 and 4. The PVDF-g-P[AMA-comb-DMAPS] membrane was synthesized via UV-initiated thiol-ene click reaction of 1,6-hexanedithiol (HDT) with the PVDF-g-PAMA membranes, using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as the photoinitiator, followed by thiol-Michael addition reaction of the zwitterionic molecules, N,N'-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate (DMAPS). A significant reduction in microbial adhesion was observed on the PVDF-g-P[AMA-comb-DMAPS] membrane in a flow chamber, in comparison to the pristine hydrophobic PVDF membrane.