Synthesis of polyisoprene, polybutadiene and Styrene Butadiene Rubber grafted silica nanoparticles by nitroxide-mediated polymerization

We present a new application of nitroxide mediated polymerization (NMP) for grafting of various elastomers onto the surfaces of silica nanoparticles (NPs) while ensuring colloidal stability and thus avoiding particle aggregation. While NMP has been used to graft chains from NP surfaces, our novel contributions are thus two-fold. We show for the first time that this methodology, initially demonstrated for styrene polymerization, can be extended to a variety of other relevant polymer chemistries, i.e., to isoprene, butadiene and styrene-butadiene rubber. We optimize the synthesis conditions for the different monomers under critical pressure conditions and characterize the grafted chains in solution by a combination of small angle x-ray and neutron scattering (with deuterated solvent labelling) to quantitatively describe the grafted chain composition. Second, crucially, we characterized the colloidal stability of the particles during the different steps of the grafting process. We have found that particle aggregation can (and does) occur at a variety of points during synthesis, and hence we have performed a detailed refined characterization of NP agglomeration and then found methods to mitigate it at each stage. These steps ensure that we can begin the preparation of composite materials from a well-defined starting point. [Display omitted]