Organic/Inorganic Nanocomposite Star Polymers via Atom Transfer Radical Polymerization of Methyl Methacrylate Using Octafunctional Silsesquioxane Cores

A method was developed for atom transfer radical polymerization (ATRP) synthesis of a nanocomposite consisting of dispersed, nanosized hard particles in a thermoplastic matrix. Octafunctional cubic silsesquioxanes were used as a platform to synthesize 8-arm star poly(methyl methacrylate) (PMMA) via ATRP. The cubic silsesquioxane, octakis(hydridodimethylsiloxy)octasilsesquioxane (Q 8 M 8 H ), was converted to either octakis(2-bromo-2-methylpropionoxypropyldimethylsiloxy)octasilsesquioxane (OBPS) or the octaethylbenzyl chloride analogue. The bromo ester was successfully employed as an ATRP initiator using CuCl as catalyst, leading to formation of PMMA arms with controlled molecular weights and hence to nanocomposites with essentially complete control of dispersion and solids loading. The catalyst and initiator concentrations were demonstrated to affect the molecular weight distribution and the occurrence of star−star coupling caused by inevitable termination reactions.