Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto anatase TiO 2 nanoparticles via a combination of phosphate ligand engineering and alkyneazide ''click'' chemistry. Highly crystalline TiO 2 nanoparticles with 5 nm diameter were synthesized by a solvothermal method and used as high refractive index filler. The synthesized phosphate-azide ligand anchors strongly onto the TiO 2 nanoparticle surface and the azide end group allows for attachment of poly(glycidyl methacrylate) (PGMA) polymer chains through an alkyne-azide ''click'' reaction. The refractive index of the composite material increased linearly from 1.5 up to 1.8 by increasing the loading of TiO 2 particles to 30 vol % (60 wt %). UV-vis spectra show that the nanocomposites exhibited a transparency around 90% throughout the visible light range. It was also found that the PGMAgrafted TiO 2 nanoparticles can be well dispersed into a commercial epoxy resin, forming transparent high refractive index TiO 2 -epxoy nanocomposites.

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This study demonstrated a method for toughening a highly crosslinked anhydride cured DGEBA epoxy using rubbery block copolymer grafted SiO 2 nanoparticles. The particles were synthesized by a sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The inner rubbery block poly(n-hexyl methacrylate) (PHMA) had a glass transition temperature below room temperature. The outer block poly(glycidyl methacrylate) (PGMA) was matrix compatible. A rubbery interlayer thickness of 100% and 200% of the particle core radius was achieved by grafting a 20 kg/mol and a 40 kg/mol PHMA at a graft density of 0.7 chains/nm 2 from the SiO 2 surface. The 20 kg/mol rubbery interlayer transferred load more efficiently to the SiO 2 cores than the 40 kg/mol rubbery interlayer and maintained the epoxy modulus up to a loading of 10 vol% of the rubbery interlayer. Both systems enabled cavitation or plastic dilatation. Improvement of the strain-to-break and the tensile toughness was found in both systems. We hypothesize that plastic void growth in the matrix is the primary mechanism causing the improvement of the ductility. OPEN ACCESSPolymers 2012, 4 188

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