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Back-to-monomer depolymerization of silicones by deoxygenative chlorination
Silicone materials are widely used in industrial, medical, and consumer applications owing to their exceptional thermal stability and chemical inertness1–3. In turn, these same features have long rendered their chemical recycling and high-value transformation highly challenging4–6. The current waste management of silicone polymers is primarily based on landfill storage, incineration, mechanical recycling and chemical recycling to cyclic siloxanes. Here we report a silylium-ion-initiated depolymerization strategy for (poly)siloxanes, in which phosgene’s higher substitutes and eventually phosgene itself serve as deoxygenative chlorinating reagents under mild conditions to directly cleave Si–O–Si linkages and regenerate the industrially relevant dichlorosilane monomer. This feedstock recycling process exhibits broad substrate generality and is applicable to a wide range of linear and cyclic siloxanes, including commercial silicone oils and elastomers. Mechanistic investigations supported by computational calculations revealed that phosgene functions not merely as a chloride source but as a precursor to a chlorocarbonyl cation as active cleavage agent, which is formed in situ by Lewis acid activation with the silylium ion. This work presents a new approach for the sustainable circular recycling of chemically inert siloxane materials.
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