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Self-Assembly of Polymer-Brush-Decorated Particles Synthesized by Surface-Initiated Living Radical Polymerization
Kohji Ohno
Institute for Chemical Research
Kyoto University, Uji, Kyoto 611-0011, Japan
Synthesis and self-assembly of fine particles grafted with well-defined polymer brushes are presented. Monodisperse silica particles (SiPs) of various diameters were surface-modified with a newly designed triethoxysilane having an initiation site for living radical polymerization, for instance, (2-bromo-2-methyl)propionyloxyhexyl triethoxysilane for atom transfer radical polymerization (ATRP). The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex proceeded in a living manner in all examined cases, producing SiPs coated with well-defined PMMA of a target molecular weight with a graft density as high as 0.7 chains/nm2. These PMMA-SiP hybrid particles had an exceptionally good dispersibility in organic solvents.
A colloidal crystal was newly identified for a liquid suspension of the PMMA-SiP hybrid particles. With increasing particle concentration, the suspension progressed from a (disordered) fluid to a fully crystallized system, going through a narrow crystal/fluid coexisting regime. The crystal had a face-centered-cubic structure with a surprisingly large nearest-neighbor interparticle distance, suggesting that the graft chains, highly extended due to the “concentrated brush effect”, exerted a long-range steric interaction. The crystalline structure was of closed-packed type in all cases, and the nearest-neighbor interparticle distance in the crystal increased with increasing graft chain length. Liquid-crystal formation of anisotropic particles grafted with polymer brush are also discussed.