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ABSTRACT:In this article, we consolidate several literature reports in an attempt to provide a structural definition of a polymer brush as a tethered polymer layer with a high grafting density of polymer chains. We will try to distinguish a brush from grafted polymer layers and coated layers and provide a reasonable approach to the description of the brush regime with a single parameter S-reduced grafting density. Furthermore, we will attempt to describe the relevance of this description to applications. This article is timely given the continuing interest relating to brushes on flat substrates, nanoparticles, and the walls of micro-channels.

Reversible addition fragmentation chain transfer (RAFT) has been used to synthesize polymer brushes. Styrene, methyl methacrylate, and N,N-dimethylacrylamide brushes were prepared under RAFT conditions using silicate surfaces that were modified with surface-immobilized azo initiators. Films with controlled thicknesses were produced. RAFT was also used to synthesize PS-b-PDMA and PDMA-b-PMMA block copolymer brushes that displayed reversible surface properties upon treatment with block-selective solvents.

PMMA-layered silicate nanocomposites were prepared by in-situ suspension polymerization and emulsion polymerization. For the suspension polymerization, the silicate layers were dispersed individually in water, and we speculate that they are adsorbed on the surface of monomer droplets. For the emulsion polymerization, the nanocomposite was obtained by adding an aqueous dispersion of layered silicate into the polymer emulsion. Wide-angle X-ray diffraction (WAXD) and atom force microscopy (AFM) were used to characterize the structures of the nanocomposites. Analysis of samples from emulsion and suspension polymerization was consistent with an exfoliated structure; after melt pressing, WAXD analysis indicated that both intercalated and exfoliated structures were observed. The exfoliated structure was preserved when organic modifiers that produced tethered polymer chains were used. Compared to a PMMA macrocomposite, the nanocomposites prepared by these methods display glass transition temperatures that are up to 15 °C higher and thermal degradation temperatures that are up to 60 °C higher.

Surface initiated polymerizations yield covalently bonded polymer on the substrate. The properties of such nanoparticles are unique finding a wide range of applications. This article reviews the different techniques of synthesis of these hybrid nanoparticles and their mechanistic approach presented in literature.