Synthesis of polymer brushes on silicate substrates by radical addition fragmentation chain transfer technique

The objective of this research was to investigate controlled radical polymerizations for the synthesis of polyacrylamides and to apply these techniques in polymerization from surface-immobilized initiators. The interest in surface-immobilized polyacrylamides was two-fold: fundamental interest in tethered chains and commercial applications in chromatography supports and surface modification of biomedical devices. Before investigating surface-immobilized polymerizations, controlled free radical reactions were studied in solution. Initially, ATRP was used for the polymerization of N, N-dimethylacrylamide (DMA). All reactions were uncontrolled affording broad polydispersity polymers with a lack of agreement between experimental and theoretical M _n. Mass spectrometry, 1H NMR and sequential monomer addition experiments confirmed the uncontrolled nature of these reactions. This behavior was attributed to complexation of the metal catalyst with the acrylamide moiety leading to a slow-down of the ATRP deactivation step.; Polymerization of DMA via RAFT, which does not require metal catalysts, was investigated as an alternate route. Solution polymerizations of DMA via RAFT were controlled. This method was subsequently applied to the synthesis of polymer brushes from a surface-immobilized azo-type initiator. Styrene, MMA, and DMA were polymerized under RAFT conditions from the silica gel and flat silicon substrates, giving polymer films with controlled thickness. These thin polymer films were analyzed by ATR-FTIR, ellipsometry, tensiometry, XPS and TGA. The immobilized chains were cleaved from the surface via transesterification with methanol and analyzed by GPC to give chains with controlled molecular weight and relatively narrow polydispersities. The use of RAFT in synthesis of covalently attached polymer chains also allowed the formation of block copolymer brushes by the sequential addition of monomers, which further demonstrated the controlled nature of this system. Amphiphilic PS-b-PDMA and PDMA-b-MMMA copolymer brushes showed reversible rearrangement behavior upon treatment with different solvent systems.