Customizing Polymer Brushes

Abstract

Chemistry One way to modify a surface and control or improve its properties is to grow polymer chains off the surface to form a brush. One method for growing polymer brushes from surfaces—atom-transfer radical polymerization—can be controlled electrochemically, in that the process can be catalyzed by Cu+ ions but not by Cu2+. Li et al. used this method to create gradients in the length of polymer brushes grown on a substrate modified with a suitable initiator. They polymerized 3-sulfopropyl-methacrylate with Cu+-bipyridyl catalysts generated from Cu2+ in a mixed water-methanol solvent. The substrate was placed opposite a working electrode in an electrochemical cell. Because the Cu+ catalyst diffused toward the substrate, a concentration gradient was established along the cell. If the substrate was placed parallel to the working electrode, uniform brushes were grown, but if it was placed at an angle, a gradient in polymer brush length (measured with ellipsometry) was created, corresponding to the gradient in catalyst concentration. Prepatterning of the initiator on the substrates—which included gold, silicon, and silicone rubber—allowed the brush to form a staircase structure. J. Am. Chem. Soc. 10.1021/ja3116197 (2013).