Kinetics of Surface-Initiated Atom Transfer Radical Polymerization of Acrylamide on Silica

Surface-initiated atom transfer radical polymerization (ATRP) of acrylamide is achieved on silica at room temperature by using a catalytic system of CuCl/CuCl2/tris(2-dimethylaminoethyl)amine. The thickness of the polyacrylamide film is proportional to the monomer concentration but not to reaction time. This behavior is qualitatively similar to that for surface ATRP of acrylamide using a CuCl/bipyridine catalytic system, which required 130 °C for initiation. A kinetic study shows that, at room temperature, both the rate for chain propagation and the rate of chain termination are higher, despite a much higher concentration of Cu(II) to reduce the radical population at room temperature. XPS shows that the concentration of chlorine at the surface drops as the polymerization reaction progresses, indicating that termination is caused by radical combination. For polymerization on silica gel at room temperature, microanalysis shows that half of the chlorine is lost during polymerization. Equilibration of the surface-bound initiator with only the copper catalyst shows that most of the chlorine loss is due to the combination of initiator radicals.