Effect of different alkoxy POSSs on thermal stability and mechanical properties of silicone rubber

Six varieties of alkoxy polyhedral oligomeric silsesquioxanes (POSSs) featuring methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, and n-hexoxy as terminal groups were synthesized using the direct dehydrogenation condensation method. These POSSs were then incorporated as cross-linking agents into hydroxy-terminated polydimethylsiloxane (HPDMS) to create various formulations of room temperature vulcanized silicone rubbers (RTV SRs), denoted as SRM, SRE, SRP, SRI, SRB, and SRH. The morphology, thermal stability, and mechanical properties of the resulting SRs are analyzed using scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and universal tensile testing machine. The findings indicate that the incorporation of POSS into SRs results in significant enhancements in thermal stability and mechanical properties when compared to the control group (TEOS/SR). SRB and SRH exhibit the highest cross-linking density and tensile strength. Specifically, SRB-4 demonstrates the highest tensile strength at 2.66 MPa, representing an 8.6-fold increase compared to TEOS/SR. The maximum decomposition rate temperature of SRP-4 reaches 527°C and is 194°C higher than TEOS/SR. Because the alkoxy groups with different chain lengths on POSS have different chemical reactivity, they have a great effect on the dispersion of POSS in SRs, which affect the cross-linking density, tensile strength, and thermal stability.