Adhesion Enhancement of Polymeric Films on Glass Surfaces by a Silane Derivative of Azobisisobutyronitrile (AIBN).
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Adhesion of polymeric films on surfaces can be due to a combination of van der Waals, electrostatic or covalent interactions between the two materials. The interfacial adhesion between a polymer film and glass or metal can be improved by using a broad class of silane coupling agents. Typically, silane coupling compounds used for adhesion improvement have structure similar to (R´O)3-Si-R, where R´O- is an alkoxy group and -R is an organofunctional group. Under appropriate reaction conditions alkoxy groups condense with hydroxyl groups available on the surface, resulting in surfaces decorated with organofunctional -R groups, which promote formation of covalent bonding of the coupling agent with polymeric networks. Alkoxy silanes with amino and vinyl organofunctional groups are common silane coupling agents and their adhesion-promoting abilities with polymeric films have been well-documented. In analogy to our previous work of forming conformal polymer coatings on three dimensional assemblies of silica nanoparticles (aerogels) via surface initiated polymerization (SIP), here we expand the scope of that work demonstrating the application of a new bidentate free radical initiator (Si-AIBN) as coupling agent that enhances adhesion of polystyrene (PS) and polymethylmethacrylate (PMMA). Si-AIBN was synthesized via a condensation reaction between 3-aminopropyltriethoxysilane (APTES) and azobiscyanovaleric acid. Si-AIBN is attached to the surface of glass by hydrolysis of the ethoxy groups and reaction with the hydroxyl groups of the surface. On supply of thermal energy those glass surfaces act like a macro initiator generating surface-bound radicals. In the presence of olefin monomers, surface-bound initiator starts formation of polymeric chains in analogy to a “grafting from” approach. Since each polymer chain is terminated by a molecule of the initiator, which is surface-bound, the adhesion of the resulting polymeric films on the substrate is promoted not only by mechanical interlocking of the polymeric chains but also by covalent bonding with the glass surface.