Synthesis of Polymer/Silica Hybrid Nanoparticles Using Anionic Polymerization Techniques

Abstract

We report a new "grafting to" technique for the functionalization of silica particles with anionically produced polymers. It is based on a two-step procedure. In the first step the silica nanoparticles were modified with multifunctional chlorosilanes. This procedure allows replacing the original Si−OH surface groups by Si−Cl groups. In the second step the anionically synthesized polymers were linked to the Si−Cl functionalized nanoparticle surface. Both the chlorosilane functionalization of the nanoparticles and the subsequent reaction with living polymer can be carried out without irreversible particle aggregation. This was proved by examining the reaction products with static and dynamic light scattering as well as small-angle X-ray scattering. The polymer linking event is accompanied by termination reactions, most likely due to residual Si−OH groups. Therefore, the raw products were purified by a simple fractionation procedure. The examination of the products by size exclusion chromatography showed that this procedure allowed removing the free polymer quantitatively. The new anionic based method offers the possibility for grafting densities up to 1 chain per nm2 of particle surface, which is significantly higher than reported in the past for other "grafting to" approaches. The now obtained grafting densities are similar to the ones reported for "grafting from" techniques which are mainly based on controlled radical polymerization. Our new approach offers the possibility to obtain hybrid materials containing polymers which are not accessible via controlled radical techniques like polydienes. In addition, the new technique allows grafting polymers having molecular weights up to 500 000 g/mol and still narrow molecular weight distributions.