Effects of Ph12SQ on the thermal stability and mechanical properties of high temperature vulcanized (HTV) silicone rubber

Ph<sub>12</sub>SQ (C<sub>6</sub>H<sub>5</sub>SiO<sub>1.5</sub>)<sub>12</sub> was blended into a polydimethylsiloxane (PDMS) based HTV silicone rubber as a reinforcing filler at loadings of (0, 2.5, 5, 10, 15, 20% by weight). The thermal stabilities and mechanical properties of these HTV silicone rubber composites were studied by thermal gravimetric analysis (TGA) and tensile testing, respectively. Dispersions of Ph<sub>12</sub>SQ were characterized by scanning electron microscopy (SEM). The obtained results show the presence of SQ-rich regions that affect the thermal stabilities and mechanical properties of HTV silicone rubber. TGA shows that T<sub>d1%</sub> is delayed from approximately 215 °C for DD<sub>0</sub> to 350 °C (DD<sub>20</sub>) (about 130°C) and the T<sub>d5%</sub> mass loss exhibits a similar trend. The thermo-oxidative stability also increases with Ph<sub>12</sub>SQ weight fraction. Also, the tensile strength and elongation at break of these HTV silicone rubbers increase from 8.8 to 11 MPa and 655 to 950 % with incremental loading of Ph<sub>12</sub>SQ to 5 wt% (DD<sub>5</sub>). Moreover, the addition of Ph<sub>12</sub>SQ increases its relative permittivity from 3.2 to 14.2 and the dissipation factor at 1 MHz increases from 0.01 to 0.05. Finally, the values of T<sub>d5%</sub> at different heating rates were applied for comparison of the lifetime of DD<sub>0</sub> and DD<sub>5</sub> samples according to the D&R model. The results show that DD<sub>5</sub> offers a longer lifetime than DD<sub>0</sub> at different temperatures.

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