Surface macromolecular architectural designs using photo-graft copolymerization based on photochemistry of benzyl N,N-diethyldithiocarbamate

Surface macromolecular architectures with regional dimensional precision, control of the thickness of a graft layer, and blocks of graft chains were attempted using the surface photo-graft copolymerization method pioneered by Otsu et al. This is based on the photochemistry of benzyl N,N-diethyldithiocarbamate, which can be photolyzed into a radical pair lone radical can initiate radical polymerization and the other tends to recombine with the former radical). Ultraviolet light (UV) irradiation of a benzyl N,N-diethyldithiocarbamyl group-immobilized polymer surface in the presence of a vinyl monomer such as N,N-dimethylacrylamide, N-[3-(dimethylamino)propyl]acrylamide, methacrylic acid, or styrene at room temperature allowed precise control of the macromolecular architectures of the grafted surfaces. X-ray photoelectron spectroscopy (XPS) analyses and water contact angle measurements before and after UV irradiation in a monomer solution provided evidence that the graft copolymerization proceeded only during photoirradiation and at photoirradiated portions. Atomic force microscopic (AFM) observations showed that the thickness of the graft-copolymerized layers increased almost linearly with UV irradiation time. Patterned grafted surfaces, which were prepared using the ionic or nonionic hydrophilic monomers listed above under irradiation through a projection mask, were clearly visualized by dye-staining or cell-culturing. The graft copolymerization under irradiation through a projection mask with sequential monomer charges yielded surfaces with regionally dimensionally controlled macromolecular architectures such as di- and triblock graft-copolymerized surfaces. A graft thickness-gradient surface was obtained by using a gradient filter.