In situ thermo-dependant trapping of carbon radicals: a versatile route to well-defined polymer-grafted silica nanoparticles

Abstract

We report in this paper an original and simple method for the grafting of polymer chains on colloidal silica particles. We first synthesize an alkoxyamine bi-functional initiator, by coupling 2-methyl-2-[N-tert-butyl-N-(dimethoxyphosphoryl-2,2-dimethylpropyl)aminoxy]propionic acid (MAMA) and an acrylate coupling agent, 3-(trimethoxysilyl)propyl acrylate (TPMA). Based on the fact that MAMA dissociates at 25 °C, but activates polymerization of acrylates at only 110 °C, it is possible to stop the reaction after the insertion of only one CC acrylate double bond, in the temperature range 25–80 °C. This synthetic methodology is called “in situ thermo-dependant trapping of carbon radicals”. The “new” initiator obtained at that stage is then grafted on Stöber silica particles, by simple condensation of its alkoxysilane functions. We show that the initiator-grafting density is twice as high as the value obtained by our first approach of “trapping of carbon radicals”. The last step of the synthesis process is the grafting from polymerization of polybutylacrylate (PBA). Transmission electron microscopy (TEM) images and small-angle neutron scattering (SANS) spectra show that the PBA-grafted silica particles are spherical, with a narrow size distribution, and do not form aggregates. Moreover, by this versatile route, the grafted polymer density, the molecular weight and therefore the polymer-layer morphology, can be easily controlled and tuned. It can also be extended to other monomers that work well with SG1 nitroxide.