Radiation Induced Double Grafting of Polybutadiene Olygomers and Styrene onto Silica: Characterization of the Materials and Mechanistic Studies

Ionizing radiations from a 60-Co source have been employed for inducing radical reactions finally leading to the grafting of unsaturated olygomers and vinyl monomers onto the surface and micropores of precipitated silica Zeosil 116 5 (150- 170 m 2 /g). The target was to obtain modified silica with enhanced polar compatibility with respect to polybutadiene and styrene-butadiene copolymers rubber matrices and suited to favour the formation of chemically bound rubber in a vulcanization process. The latter property was expected to follow from the characteristics of free radical reactivity arising from the unsaturations present in the organic coating. Three classes of modified silica have been prepared: A)silica coated with polybutadiene olygomers with M n in the range 1000-5000 and having a different relative content of 1,4-cis, 1 , 4 -trans and vinyl double bonds [1,2] ; B)Silica coated with polybutadiene olygomers further modified by subsequent grafting of styrene monomer. The type A samples were obtained by γ irradiation under vacuum of silica samples preimpregnated with the oligomers in the dose range up to 30-200 kGy. Type B samples were obtained via three different steps as outlined in the scheme below: SiO 2 (PB) γ vacuum→/298K SiO 2 -PB γ air→/298K SiO 2 -PB-OOH Fe 2+ →/Sty SiO 2 -PB-O-PS The characterization of the modified silica was carried on by elemental and thermogravimetric analysis, FTIR (diffuse reflectance), Raman spectroscopy, inverse gas chromatography (IGC), CP/MAS 29-Si NMR, granulometry and TEM microscopy.