¹³C and ²⁹Si Solid-State NMR of Rubber−Silica Composite Materials

The polymer−silica interaction in elastomeric materials composed of 1,4- cis -polyisoprene rubber and silica was studied by magic angle spinning NMR. The relaxation times in the hydrogen domain are informative about phases at the nanometer scale when a spin propagation phenomenon, due to strong dipolar couplings in the solid, prevails. However, magnetization diffusion is quenched in a rubbery phase where spin−spin relaxation rates are slow. The problem was overcome by promoting spin diffusion below the glass transition at low temperature. The interface was then observed under high-resolution conditions by the reciprocal points of view of 13 C and 29 Si nuclei. In particular, a fast transfer of magnetization from the polymer to the silica surface was observed by cross-polarization dynamics following the nonprotonated silicon atoms. Bidentate coupling agents and vulcanization promote a better interaction with the silica surface. The morphological modifications of the silica particles after processing could also be observed.