Viscoelastic behavior of poly(butyl methacrylate) densely grafted on silica nanoparticles

A series of poly(butyl methacrylate)s (PBMAs) with various molar masses (33 000–270 000 g mol −1 ), which were densely grafted on fumed silica nanoparticles (PBMA–SiO 2 ), were synthesized by surface‐initiated atom transfer radical polymerization. The dynamic viscoelastic behavior of PBMA–SiO 2 was systematically investigated in the solid and molten states with oscillatory strains, and compared to that of a conventional nanocomposite (PBMA/SiO 2 ). The storage moduli of PBMA–SiO 2 and PBMA/SiO 2 are equivalent in the solid state, whereas the storage modulus of PBMA–SiO 2 is lower than that of PBMA/SiO 2 in the molten state, especially at high silica loading. This is because the formation of a network structure composed of the silica nanoparticles in PBMA–SiO 2 is strongly suppressed by the polymer brushes on the particles. In contrast, even at low silica loading, the PBMA–SiO 2 system exhibits a gel‐like behavior resulting from a steric repulsion between the composite particles, because all of the tethered polymers behave as bound polymers. Copyright © 2011 Society of Chemical Industry