High-performance silicone elastomers via microphase separation: strong, heat resistant, flame retardant and transparent

High-performance room-temperature vulcanized (RTV) silicone elastomers that simultaneously possess superior mechanical strength, thermal stability, and excellent transparency are urgently required in advanced engineering fields. Current strategies mainly rely on incorporating inorganic fillers or utilizing complex macromolecular cross-linkers; however, their serious aggregation issues and complicated synthesis significantly restrict their practical use, especially in optical applications. Inspired by the Flory–Huggins theory, we first propose a straightforward yet highly effective "one-stone-three-birds" molecular design strategy, employing a linear intermediate-molecular-weight cross-linker (Si-40) with multiple reactive ethoxy groups to remarkably improve the performance of RTV silicone elastomers. This approach achieves nanoscale microphase separation instead of undesirable macroscopic aggregation in silicone rubber. Experimental results demonstrate substantial improvements in mechanical properties (488 % increase in tensile strength), thermal stability (46.3 % increase in residual yield at 800 °C), and flame-retardant performance (16 % reduction in peak heat release rate) compared to traditional systems. Detailed investigations into the pyrolysis behavior and condensed-phase evolution revealed that Si-40 plays a dual role in enhancing thermal stability and flame retardancy. Specifically, it inhibits the occurrence of random main-chain scission while sustaining radical-induced cross-linking reactions throughout thermal decomposition. Simultaneously, Si-40 promotes the development of a more compact and continuous char residue, which serves as an effective physical barrier to retard heat transfer and suppress smoke release during combustion. This facile and scalable molecular design approach provides a novel and versatile route toward designing high-performance silicone elastomers for advanced applications, including flexible electronics and thermal protective coatings.