  We present a new convenient and efficient "grafting from" method to obtain
well defined polystyrene (PS) silica nanoparticles. The method, based on
Nitroxide-Mediated Polymerization (NMP), consists to bind covalently the
alkoxyamine, which acts as initiator controller agent, at the silica
nanoparticles surface in two steps. The first step is a reaction between the
aminopropylsilane and the silica particles in order to functionalize the
particles surface with amino group. In a second step, the
initiating-controlling alkoxyamine moiety is introduced via an over grafting
reaction between the amino group and the N-hydroxysuccinimide based MAMA-SG1
activated ester. To simplify both their chemical transformation and the
polymerization step, the native silica particles, initially dispersed in water,
have been transferred in an organic solvent, the dimethylacetamide, which is
also a good solvent for the polystyrene. The synthesis parameters have been
optimized for grafting density, conversion rates, and synthesis reproducibility
while keeping the colloidal stability and to avoid any aggregation of silica
particles induced by the inter-particles interaction evolution during the
synthesis. After synthesis, the final grafted objects have been purified and
the non-grafted polymer chains formed in the solvent have been washed out by
ultra filtration. Then the particles have been studied using Small angle
Neutron Scattering (SANS) coupled to neutron contrast variation method. To
optimize the contrast conditions, both hydrogenated and deuterated monomers
have been used for the synthesis. A refined fitting analysis based on the
comparison on two models, a basic core-shell and the Gaussian Pedersen model,
enables us to fit nicely the experimental data for both the hydrogenated and
deuterated grafted case. Differences are seen between grafting of normal or
deuterated chains which can be due to monomer reactivity or to neutron contrast
effect variations. The synthesis and the characterization method established in
this work constitute a robust and reproducible way to design well defined
grafted polymer nanoparticles. These objects will be incorporated in polymer
matrices in a further step to create Nanocomposites for polymer reinforcement.
