Multi-functionalization of poly(vinylidene fluoride) membranes via combined "grafting from" and "grafting to" approaches

PVDF-g-[PBIEM-co-PPMA] graft copolymers were first synthesized in a "grafting from" process, involving thermally induced graft copolymerization of two inimers, 2-(2-bromoisobutyryloxy) ethyl methacrylate (BIEM) and propargyl methacrylate (PMA), from ozone-preactivated poly(vinylidene fluoride) (PVDF) chains. Microporous membranes were fabricated from the PVDF-g-[PBIEM-co-PPMA] copolymers by phase inversion in an aqueous medium. The tertiary C-Br groups of BIEM repeat units and the propargyl groups of PMA repeat units on the PVDF-g-[PBIEM-co-PPMA] membrane and pore surfaces provided the respective functionalities for the "grafting from" process involving surface-initiated atom transfer radical polymerization (ATRP) of the viologen-containing monomer, N-benzyl-N'-(4-vinylbenzyl)-4,4'-bipyridium dichloride (BVbpy), and the "grafting to" process involving alkyne-azide click reaction with azido-terminated poly(N-isopropylacrylamide) (PNIPAM-N-3), prepared a priori via reversible addition-fragmentation chain transfer (RAFT) polymerization. The resulting PVDF-g-[P(BIEM-g-PBVbpy)-co-P(PMA-click-PNIPAM)] membrane exhibited both redox-and temperature-dependent permeability to aqueous solutions. Alternatively, metal ions, such as Ag, Au or Pt ions, can be immobilized and reduced within the viologen-containing PBVbpy brushes on the PVDF-g-[P(BIEM-g-PBVbpy)-co-PPMA] membrane. The functionalized PVDF-g-[P(BIEM-g-PBVbpy)-co-PPMA]-Ag membrane surfaces were shown to be effective in reducing bacterial adhesion and fouling under continuous-flow conditions.