Synergistic enhancement of thermal and optical properties of phenyl liquid silicone rubber reinforced by liquid phenylethyl/H‐containing <scp>POSS</scp>

Abstract A series of addition‐type liquid silicone rubbers (LSRs) with varying compositions was prepared by incorporating phenylethyl/H‐containing polyhedral oligomeric silsesquioxane (Ph/H‐POSS) as both a reinforcing filler and a crosslinking agent. The effects of Ph/H‐POSS content on the morphology, thermal stability, mechanical properties, and optical performance of the LSRs were systematically investigated. The results indicated that the thermomechanical properties of the LSRs are significantly influenced by the amount of Ph/H‐POSS incorporated. Specifically, introducing an appropriate amount of Ph/H‐POSS enhanced the crosslinking density of the LSRs. The steric hindrance caused by both the POSS structure and the phenyl groups inhibited the migration of polysiloxane chains, leading to improved thermomechanical properties. When the Ph/H‐POSS content reached 6 wt%, the T 5% and T max of the LSRs increased by 72.8 and 11.5 °C, respectively, compared to the POSS‐free LSR (LSR‐0), and the residue at 800 °C also increased. Notably, when the Ph/H‐POSS content reached 15 wt%, the elongation at break improved by up to 78.38%, compared to the pure sample. Moreover, the liquid Ph/H‐POSS exhibits excellent compatibility with the LSR matrix, ensuring good dispersion within the system with minimal impact on optical properties. The UV transmittance remains above 92%, and the refractive index of the LSRs can be adjusted by varying the Ph/H‐POSS content. This innovative approach to LSR preparation provides a promising method for developing highly elastic, transparent LSRs with tunable properties, making them suitable for applications such as electronic device encapsulation and LSR lenses.