RTV silicone rubbers cured by polyhedral oligomeric silsesquioxane and ladder-like polysilsesquioxane: Thermostability, long-term thermal properties, and pyrolysis mechanism

At present, silicone rubber has been widely used in the fields of aerospace and electronic materials, yet its long-term thermal performance still remains a challenge. In this investigation, polyhedral oligomeric silsesquioxane and ladder-like polysilsesquioxanes with multiple silicon-methoxy groups (MSPOSS, MSLPSQ) were synthesized successfully and used as cross-linkers to cure room temperature vulcanized silicone rubber (POSS-SR, LPSQ-SR). The results demonstrate that both MSPOSS and MSLPSQ can effectively improve thermostability, mechanical properties, and long-term thermal properties of RTV silicone rubber. The silicone rubber exhibits a remarkable preservation of strength and flexibility after long-time heat treatment at 400 °C. The silicone rubber demonstrates an impressive retention rate of 84.52% for tensile strength and 69.16% for elongation at break. An analysis of the pyrolysis process of the silicone rubber reveals that the 'back-biting' of polysiloxane chains were inhibited effectively by both MSPOSS and MSLPSQ. As a result of this inhibition, the silicone rubber's terminal chains are delayed from decomposing, resulting in retardation of initial thermal decomposition and significant improvement long-term thermal properties. This work may provide a new prospect for room temperature vulcanized silicone rubber for aerospace applications in extreme environments.