Grafting of polymers to solid surfaces by using immobilized methacrylates

In this paper we present the results of studies that aim at a better understanding of the radical graft polymerizations for the formation of polymer monolayers at solid surfaces by copolymerization of monomers in solution with monomers immobilized at the surface of the substrate. Monolayers of 3-methacryloylpropyl trimethoxysilane (MPS) were deposited onto silicon wafers and polymer monolayers were attached to these surfaces by copolymerization of the immobilized double bonds with styrene using azobis isobutyronitrile (AIBN) as the initiator. In two separate sets of experiments the polymerization time and the initiator concentration were varied, while all other polymerization parameters were kept constant. It was found by varying the polymerization time that the formation of the polymer layer levels off at rather low monomer and initiator conversion, and films of 15 nm thickness are formed. It was further found, that the initiator concentration (varied over almost three orders of magnitude) does not influence the thickness of the resulting films. A model is developed that explains these findings in the light of the reaction kinetics of the surface attachment reaction.