Preparation and characterization of incompletely condensed POSS and its application in RTV composites

Research on the structure and properties of room-temperature vulcanizated silicone rubber (RTV) composites with a type of incompletely condensed polyhedral oligomeric silsesquioxane (POSS) was conducted. Trisilanolphenyl POSS (TPOSS) was synthesized and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), proton nuclear magnetic resonance ( 1 H NMR), and scanning electron microscopy (SEM). FTIR spectra suggested successful bonding of TPOSS. XRD analysis illustrated that POSS exhibited a crystal behavior while TPOSS had an amorphous structure. The chemical shift of 1 H NMR at 7.1–7.8 ppm and 3.71–3.73 ppm further confirmed the structure of TPOSS. TPOSS particle was aggregated with large size observed from SEM Then, TPOSS was applied in RTV composites. Properties of RTV/TPOSS composites such as swelling behavior, tensile strength, elongation at break, thermal stability, and flame retardance were researched and compared. Results showed that the TPOSS were beneficial for increasing the cross-linking points and forming the effective three-dimensional networks in RTV composites. Tensile tests revealed that the tensile strength of RTV/TPOSS-3 was 20% higher than that of pure RTV, and the elongation at break of RTV/TPOSS-1 also showed an improvement. Thermogravimetric analysis studies demonstrated that RTV/TPOSS-5 presented the highest values of temperature at 5% mass loss and temperature at maximum mass loss rate of 437.5°C and 573.7°C, respectively. In addition, the residue of RTV/TPOSS-9 increased to 61.0%. Horizontal burning test found that the burning rate with 9% content of TPOSS was strikingly decreased by 66.4% compared with pure RTV.