Upcycling of Silicone Rubber into Value‐Added Polyborosiloxane via Boron‐Assisted Mechanochemistry

Silicone rubber is indispensable in modern life owing to its exceptional thermal resistance, chemical inertness and long-term stability. However, the robustness of its Si-O-Si backbone makes it among the most difficult materials to recycle, leading to persistent waste accumulation and serious environmental concerns. Herein, we report a boron-assisted thermomechanical scission (BATS) upcycling strategy that directly converts crosslinked silicone rubber waste into high-value polyborosiloxane (PBS), a classic strain-rate-responsive material known as Silly Putty. Under mild conditions, BATS cleaves Si-O-Si backbones and reconstructs them into dynamic Si-O-B linkages, transforming silicone rubber waste into a high-value dynamic polymer through a solvent-free, byproduct-free process. Because this boron-assisted scission process acts directly on siloxane chains, it is broadly applicable to diverse silicone rubber wastes and can be implemented using conventional polymer-processing equipment. Moreover, the resulting PBS exhibits practical utility in impact protection and rate-responsive sensing. To the best of our knowledge, the BATS strategy appears to be the first example of direct polymer-to-polymer upcycling of silicone rubber waste into a substantially higher-value material. This work establishes a general, scalable, and sustainable polymer-to-polymer upcycling platform for silicone rubber waste and offers a promising strategy for advancing a circular organosilicon economy.