Membranes that deliver nanoscale size selectivity are desirable for applications ranging from water treatment to molecular separations. Here we describe polymer thin film composite membranes coated with amphiphilic graft copolymers consisting of a poly(vinylidene fluoride) (PVDF) backbone and poly(oxyethylene methacrylate) (POEM) side chains, PVDF-g-POEM. Transmission electron microscopy and thermal analysis reveal that these materials molecularly self-assemble into bicontinuous nanophase domains of semicrystalline PVDF, providing structural integrity, and poly(ethylene oxide) (PEO), providing selective transport channels of defined size. PVDF ultrafiltration membranes coated with PVDF-g-POEM wet instantaneously and reject >99.9% of emulsified oil from a 1000 ppm oleic acid/triethanolamine/water microemulsion feed at 66 psi without fouling. Their molecular sieving capability is demonstrated through separation of like-charged organic dyes varying in molecular dimensions by several angstroms. Thicker films of PVDF-g-POEM also act as a chromatograph, exhibiting time-dependent permeation of vitamins B2 and B12. Nonporous asymmetric membranes prepared by immersion precipitation of PVDF/PVDF-g-POEM blend solutions exhibit separation capability similar to that of the thin film composites. These new nanochannel membranes hold potential utility for both high volume and high end value liquid-based separations.

Immobilization of N-methyl-D-glucamine (NMDG) on poly(vinylbenzyl chloride) beads yields an effective and highly selective sorbent for arsenate ions. Three important parameters in the resin's high As(V) affinity and selectivity are the structure of the ligand, its ionic form, and the crosslink density of the polymer. The NMDG resin crosslinked with 2 wt % divinylbenzene is far more selective than commercially available analogues, especially when sulfate and chloride ions are present in solution at high concentrations. Selectivity studies at neutral pH indicate that the protonated tertiary amine moiety is an important component of the complexation mechanism. The NMDG resin also has a high affinity for the un-ionized As(V) species at pH 1.