Generation and Characterization of Photopolymerized Polymer Brush Gradients

Abstract

A novel method for using photoiniferter-mediated photopolymerization techniques to create surface-bound macromolecular assemblies exhibiting position-dependent molecular weights, surface densities, and layer thicknesses has been developed. By using a variable photomasking system and judiciously selecting photopolymerization parameters, such as monomer concentration and light intensity, poly(methyl methacrylate) (PMMA) surfaces exhibiting layer thickness gradients were photopolymerized on single silicon substrates from self-assembled monolayers of photoiniferter. The ability to precisely control the topographic slope of a surface-tethered polymer brush gradient was achieved by varying surface irradiation time or bulk monomer concentration. Kinetics of surface-gradient formation were measured using variable angle ellipsometry as well as transmission Fourier transform infrared spectroscopy. Under the conditions studied, the photopolymerization of PMMA exhibited first-order dependence of polymer brush layer thickness on both monomer concentration and surface irradiation time even though the polymer chain ends could not be reinitiated as should occur with a living-radical system.