The role of silica in radiation induced grafting and crosslinking of silica/elastomers blends

When silica/polybutadiene and silica/styrene-butadiene are submitted to γ irradiation at 77 K a scavenging of the silica radiolytic species by absorbed vinyl units takes place at the surface with concomitant grafting and crosslinking of the polymers. Key intermediate in such reactions are SiO₂-bonded radicals of structure SiO₂–C^?(CH₃)CH(R)(R′). The role of silica is rationalized in terms of the following steps: a) absorption of the radiation energy in the bulk of the silica particles followed by exciton migration at the surface; b) reactions of excited groups (silanols) with absorbed vinyl units giving SiO₂-bonded radicals; c) crosslinking of the polymers initiated by grafted radicals.