Surface-grafted hyperbranched polymers via self-condensing atom transfer radical polymerization from silicon surfaces

A novel synthetic concept for preparing hyperbranched polymers on a planar surface is described, in which a silicon wafer grafted with an initiator layer composed of an alpha -bromoester fragment is used for a self-condensing vinyl polymerization (SCUP) via atom transfer radical polymerization (ATRP). A large number of nanoscale protrusions were found on the surface obtained by (meth)acrylic AB* initiator-monomers ("inimers"). The variations of the size and density of the protrusions, as well as the film thickness, depend on the catalyst system and show a slight correlation with the degree of branching and molecular weight of the ungrafted polymers, as confirmed by scanning force microscopy (SFM). The surface roughness is much larger than that of polymer brushes obtained by polymerizing conventional (meth)acrylates. The copolymerization of an AB* inimer and a conventional vinyl monomer gave an intermediate surface topography between the polymer protrusions and the polymer brush, which may be due to the highly branched structure. X-ray photoelectron spectroscopy (XPS) was used to determine the surface chemical composition. We find significant differences in the intensity of the bromine peak between the linear polymer brush, the branched, and the hyperbranched polymers, suggesting the feasibility of controlling the surface chemical functionalities.