Silica Surface Modification And Preparation Of Polybutadiene/SiO₂ Nanocomposites By Anionic In Situ Polymerization

Silane coupling agents are used to modifiy the fumed silica surface and organic silicas with good hydrophobility are obtained. The anionic in situ polymerization is firstly applied to introduce silicas into the preparation of polybutadiene (PB)/SiO₂ nanocomposites (NC). In this paper, the effect of silica on the structure and properties of the composites are investigated systematically.(1) The organic silicas with good hydrophobility are obtained by the modification of silane coupling agents. To vary the modification conditions, such as solvent, temperature, hydrolysis time of the agents and the PH value of the solution and apply the method of area integral ratio, to determine the optimum surface modification techniques.FTIR, TEM, TGA and UV are applied to characterize the microstructure, morphology, moisture absorption and ultraviolet absorption property. The results show that the hydroxyl group on the silica surface is reduced dramatically after surface modification. In comparison with the unmodified silica and the organic silica R972 obtained from Degussa, the dispersed state of the modified silica is much better, the size of aggregate is smaller (below 100 nm) and the nanoparticle chain structure can be observed. Different silane coupling agents have different influence on the modification and the micromorphology of the particles. The hydrophobility is increased and the moisture absorption is decreased with the increasing usage of silane coupling agent, which provides the feasibility for the anionic in situ polymerization with butadiene.(2) The anionic in situ polymerization is firstly applied to introduce silica into the polymerization of butadiene and the structure and properties of PB/SiO₂ NC are studied.FTIR, TEM and DSC are used to investigate the microstructure, morphology and glass transition temperature;TGA, dynamic rheological measurements and UV tests are applied to characterize the thermal stability, viscoelasticity and ultraviolet absorption properties of the composites. The results show that the modified silicas have a better dispersion state in PB matrix in comparison with the unmodified silica. The incorporation of the modified silica has a great influence on the microstructure of NC and different particles have different effect. The thermal stability is improved greatly, such as PB/wkl-A1100 NC, the central weight loss temperature is increased by 17.6℃ when the silica content is 3.2wt%. The formation of the spatial network of silica particles has the enhancement on the PB matrix, which also has adramatic effect on the viscoelasticity of NC: at low frequency, the storage modulus G' is increased and tanδ is decreased. The ultraviolet absorption of NC in the whole near-ultraviolet region is increased greatly, which provides the possibility for preparing anti-ultraviolet radiation rubber.The precipitated silica are used to prepare the PB/SiO₂ composites, and the results show that the NC prepared by the fumed silica is much excellent than the composites prepared by the precipitated silica both from the particle dispersed states and the material properties. In comparison with the traditional solution blending, the in situ polymerization has obvious advantage on improving the material properties.