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SYNOPSISHeterogeneous surface modification of polyacrylonitrile (PAN) ultrafiltration (UF) membranes is realized with UV irradiation-initiated graft polymerization of acrylic acid (AA) from the gas phase onto photoinitiator (benzophenone, BP)-coated samples. In the absence of monomer, PAN functionalization by ketyl radicals dominates after UV excitation of sorbed BP. With AA, graft and total polymer yield increase with B P loading and UV irradiation time. Average molecular weight and distribution of PAA homopolymer-formed in parallel during graft polymerization-are analyzed with gel permeation chromatography. Morphology of PAN-gr-AA UF membranes is checked with scanning electron micrographs (SEMs) and atomic force microscopy. Chemical changes are characterized with FTIR-ATR spectroscopy and SEM/EDX analyses, indicating a pronounced surface selectivity of the graft polymer modification (localized in the upper 5-pm membrane thickness). The amount of grafted PAA systematically reduces membrane permeability and increases dextrane retention, as verified in UF experiments. Photo graft polymer modification of U F membranes will be applied to adjust membrane performance by controlling surface hydrophilicity and permeability using other monomers and/or further graft polymer functionalization. 0 1995

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As a matrix for affinity membrane technology we chose a flat-sheet microfiltration membrane based on polypropylene. Using photopolymerization to graft epoxy groups onto the pore surface, we worked with glycidylmethacrylate as a monomer. We developed optimized, efficient, and mild UV irradiation conditions for the two-step photografting process practically preserving the given pore structure of the base membrane. A grafting degree of up to 1.2 mg/cm(2) per surface area of the membrane was obtained. The poly-propylene membrane surface became significantly more hydrophilic. Introduction of epoxy groups allowed a stable covalent immobilization of the protein streptavidin serving as receptor for affinity ligand binding. A relatively high streptavidin immobilization capacity of about 65 micro g/cm(2) per surface area of the membrane was obtained. Apparently, only about two of the binding sites of the immobilized streptavidin were available for biotin recognition. We also found that the oriented immobilization of biotinylated alkaline phosphatase onto the surface via a streptavidin bridge increased the specific enzymatic activity about sixfold compared with random immobilization of this enzyme.