Modification of Octavinyl POSS and Its Effect on the Mechanical Properties and Thermal Stability of Silicone Rubber/POSS Composites

Octavinyl polyhedral oligomeric silsesquioxane (POSS) can be used to improve the thermal stability of silicone rubber (SR). However, POSS nanoparticles tend to agglomerate in SR matrix, negatively affecting the reinforcement role of POSS for SR, and consequently limiting the practical application of SR/POSS composite. To address the issue, multifunctional POSS (m-POSS) was synthesized via a thiol-ene click reaction and used as a novel heat-resistant filler for SR. The results demonstrate that m-POSS containing both vinyl and siloxane groups was successfully synthesized, with the main product exhibiting a molecular weight of approximately 1587 g mol−1. At the POSS loading of 1.5 phr, SR/m-POSS (100/1.5) composite has much better mechanical properties and thermal stability than SR/POSS (100/1.5) composite. With increasing m-POSS loading from 1.5 to 4.5 phr, the thermal stability of SR/m-POSS becomes better, while the tensile strength decreases. SR composite filled with 1.5 phr m-POSS has an excellent balance in thermal stability and mechanical properties, with a tensile strength of 9.2 MPa and an elongation at break of 587%. To fill multifunctional polyhedral oligomeric silsesquioxane containing vinyl and siloxane groups into SR is an effective approach to producing composites with excellent properties.