Photopolymerization kinetics of poly(acrylate)-clay composites using polymerizable surfactants

Photopolymerization kinetics of polymer-clay nanocomposite systems utilizing polymerizable quaternary ammonium surfactants as dispersants were systematically investigated to determine the effects of surfactant type and clay morphology on polymerization behavior. For these studies, either polymerizable surfactants were mixed into a clay-monomer system or the surfactants were ionically anchored to clay surfaces and added to the monomer for in situ photopolymerization. Higher photopolymerization rates are observed with increasing polymerizable surfactant concentration, while no significant change or decreases in polymerization rate occur with incorporation of non-polymerizable surfactants. The higher rates observed for polymerizable surfactant systems are due to lower apparent termination rate parameters stemming from immobilization of the surfactants. For clay that is modified with ionically bonded quaternary ammonium surfactants, polymerization rates decrease in both polymerizable and non-polymerizable organoclay systems with increasing concentration, but this decrease is much smaller when polymerizable organoclays are utilized. For the same organoclay concentration, higher polymerization rates and double bond conversions result with increasing polymerizable surfactant concentration via cation exchange. Significant increases in polymerization rate also occur with increasing degree of clay exfoliation. (c) 2008 Elsevier Ltd. All rights reserved.