Synthesis Of Macromolecular Silane Coupling Agents And Its Application In Silicone Rubber

Silicone rubbers are three-dimensional structure elastomer obtained by crosslinking linear polysiloxanes, such as polydimethylsiloxanes. Silicone rubbers have high and low temperature resistance, good radiation resistance, weather resistance, and oxidation resistance, etc. Therefore, they are widely applicated in industry and many items in daily use. However, silicone rubbers have lower mechanical strength due to the weak interactions between polysiloxane molecules. Introducing polar chains in polysiloxane molecules by copolymerization to increase the intermolecular actions, adding crosslinkers to improve crosslinking network and using silane coupling agents to improve interface actions between inorganic phase and organic phase are three effective methods to improve the mechanical properties of silicone rubbers.Higher crosslinking density in silicone rubbers will be formed when crosslinkers with high vinyl content are added in rubber matrix, causing "concentrative crosslinking" effect, which could improve mechanical properties of silicone rubber.In this paper, we synthesized two kinds of macromolecular silane coupling agents (MMSCAs) which could yield both concentrative crosslinking effect and coupling function. Two types of vinyl silicone oils (VSO) with different vinyl content of allyl-capped hyperbranched polycarbosilane (HBP) and triethoxysilane (TES) were employed to synthesize MMSCAs by hydrosilylation reaction. MMSCAs and the feed materials were studied by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The performances of silicone rubbers prepared from VSOs, HBP and MMSCAs was further studied.The silicone rubber samples prepared from different crosslinkers were investigated by scanning electron microscope (SEM), crosslinking density test, mechanical properties and thermogravimetry (TG) analysis.With VSOs, HBP, MMSCAs in silicone rubber increasing, crosslinking density of silicone rubbers increased correspondingly. The ethoxyl groups in MMSCAs could react with hydroxyl groups on the surface of silica, resulting in the enhancement of the interactions between polymeric matrix and fillers.MMSCAs could offer effect of "concentrative crosslinking" in silicone rubber. MMSCAs could also enhance the interaction between organic phase and inorganic phase. Hence, they could improve mechanical performances of silicone rubber.When MMSCAs were used as crosslinkers, the silicone rubbers had lower thermal stability. It could be explained that the hydroxyl groups that were produced by ethoxyl hydrolysis accelerated the degradation of silicone matrix, especially at high temperatures.