Synthesis and characterization of novel room temperature vulcanized (RTV) silicone rubbers using octa[(trimethoxysilyl)ethyl]-POSS as cross-linker

A novel cross-linker octa[(trimethoxysilyl)ethyl]-POSS (OPS) based on a Vinyl-POSS derivative was firstly prepared via hydrosilylation chemistry. The novel POSS cross-linker was applied to hydroxyl terminated polydimethylsiloxane (HPDMS) matrix to prepare a series of novel RTV silicone rubbers. The chemical incorporation of novel POSS cross-linker into PDMS by hydrolytic condensation reaction was verified by attenuated total reflection (ATR) infrared spectroscopy. Morphology, thermal properties and mechanical properties of these novel RTV silicone rubbers have been studied by means of scanning electron microscope (SEM), thermal gravimetric analysis, universal tensile testing machine and dynamic mechanical analysis, respectively. The results displayed a pronounced enhancement effect of the novel cross-linker OPS on thermal stabilities and mechanical properties of RTV silicone rubbers as compared with the PDMS polymers prepared with tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMOS) cross-linkers. Subsequently, the thermal decomposition of representative novel RTV silicone rubber in nitrogen was monitored by TGA coupled with real-time IR, and the degradation residues were also characterized by FTIR. It was found that the POSS cages were beneficial to increasing the degradation residues. The striking enhancements in thermal properties and improvements on mechanical properties could be attributable to the synergistic effect of the increasing dimensionality of cross-linking networks resulting from three-dimensional structure of OPS cross-linker, the plasticization of self-cross-linked OPS cross-linker and uniform distribution of POSS-rich domains.