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 la yer 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 obtain ed by (meth)acrylic AB* initiator-monomers ("inimers"). The variations of t he size and density of the protrusions, as well as the film thickness, depe nd on the catalyst system and show a slight correlation with the degree of branching and molecular weight of the ungrafted polymers, as confirmed by s canning force microscopy (SFM). The surface roughness is much larger than t hat of polymer brushes obtained by polymerizing conventional (meth)acrylate s. The copolymerization of an AB* inimer and a conventional vinyl monomer g ave 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 chemica l composition. We find significant differences in the intensity of the brom ine peak between the linear polymer brush, the branched, and the hyperbranc hed polymers, suggesting the feasibility of controlling the surface chemica l functionalities.