Synthesis of Polymer Thin Film Gradient with Nanometer Thickness through Water Diffusion Controlled Surface Polymerization

Abstract

We report here a unique, simple method for synthesizing polymer film gradients with nanometer thickness through diffusion controlled surface polymerization. Polar solvents, especially water, have previously been shown to increase the rate of atom transfer radical polymerization (ATRP) of numerous monomers. That result made it apparent that the rate of ATRP polymerization could be regulated by the concentration of water in the polymerization solution. On the basis of this observation, we successfully developed a simple method for preparing polymer thin film gradients on substrates by water concentration gradient formed along the surface of substrates. An initiator attached substrate was placed in a two-layer system of water and a polymerization solution in which the diffusion of water into the polymerization solution resulted in a monomer concentration gradient, leading to varied polymerization rates along the substrate, and finally polymer thin film gradients. Poly(ethylene glycol) methacrylate (PEGMA) gradient thin films formed on silica surfaces have thickness ranging from a few of hundreds of angstroms to more than 1000 Å.