Starlike polymeric architectures by atom transfer radical polymerization: Templates for the production of low dielectric constant thin films

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The synthesis of novel poly(methyl methacrylate)s with starlike architectures by controlled radical polymerization starting from dendritic 2-, 4-, 6-, and 12-arm multifunctional initiators is described. The more highly functionalized initiators were obtained by coupling a bromo-functionalized bis-(hydroxymethyl)propionic acid (bis-MPA) first generation dendron to hydroxyl-functionalized precursors. The controlled free radical character of the atom transfer radical polymerization is supported by the remarkably low polydispersities of the polymers and the close correspondence between the calculated and measured molecular weights. NMR studies on the polymers were consistent with initiation occurring from all initiator arms for the 2-, 4-, and 6-arm derivatives. Initial studies on deuterated polymers derived from 12-arm initiator suggest that in some cases initiation was not quantitative. In addition, starlike random copolymers of methyl methacrylate containing varying amounts of hydroxyethyl methacrylate with slightly higher polydispersities have been synthesized. Preliminary results show that these copolymers can be used to produce nanophase-separated inorganic/organic hybrids by templating vitrification of methylsilsesquioxane (MSSQ) and nanoporous thin films after subsequent thermal degradation of the organic polymer. Transmission electron microscopy confirms a nanoporous morphology of the thin films, and a decrease of the dielectric constant is observed.