Method for the Depolymerization of Silicone

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This invention is a chemical recycling method that breaks down waste silicone (polysiloxane) polymers into reusable building-block molecules. The process heats a mixture of silicone waste, acetic anhydride (or acetic acid combined with phosphorus pentoxide), a swelling agent such as n-decane, and a small amount of a zinc catalyst to 160–200 °C for 30–60 minutes. This combination efficiently cleaves the silicone polymer chains, producing diacetoxydimethylsilane and related monomers that can be directly used to manufacture new silicone materials. The acetic acid generated as a by-product of monomer hydrolysis can be converted back into acetic anhydride using phosphorus pentoxide, making the overall process largely self-sustaining in reagents.

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• Chemical recycling of end-of-life silicone consumer products such as silicone baking molds, kitchen utensils, and toys to recover high-purity silicone monomers for remanufacturing.
• Recycling of industrial silicone tubing, seals, and gaskets — including fiber-reinforced composites — back into usable silicone feedstocks.
• Recovery of silicone from medical-grade silicone devices and components at end of service life, reducing hazardous waste disposal.
• Processing of mixed or colored silicone waste streams (e.g., pigmented rubbers) where conventional mechanical recycling would produce only low-quality downcycled material.
• Integration into a closed-loop silicone manufacturing process where depolymerization monomers are hydrolyzed and repolymerized on-site, with acetic anhydride reagent recovered and recycled.
• Depolymerization of silicone oils from electronics and lubrication applications to reclaim dimethylsilane monomers for new polymer synthesis.

BenefitsContent extracted from patent full text and abstract with AI.

• Achieves high depolymerization rates (up to ~90%) and monomer yields (up to ~77% diacetoxydimethylsilane) within only 30–60 minutes, far faster than comparable prior-art protocols requiring up to 300 minutes.
• Requires only catalytic amounts of zinc (as low as 1 mol%), making the process cost-effective and avoiding stoichiometric quantities of metal reagents.
• The swelling agent enables processing of crosslinked and rubber-form silicones that would otherwise resist chemical attack, broadening the range of recyclable silicone waste.
• Acetic anhydride consumed in the reaction can be regenerated from the acetic acid by-product using phosphorus pentoxide, significantly reducing reagent consumption and process costs.
• Avoids environmentally harmful reagents such as boron trifluoride or benzoyl fluoride used in prior-art methods, improving the safety and environmental profile of the process.
• Works on diverse real-world silicone waste including colored, pigmented, and composite silicone products without requiring pre-sorting or purification of the input material.

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Patent Abstract

The invention relates to a method for the depolymerization of silicones, the method comprising the steps of:a) heating a mixture comprisingi. a silicone,ii. acetic anhydride and/or a mixture of acetic acid and phosphorus pentoxide,iii. a swelling agent andiv. a zinc catalyst to a temperature of 160-200 °C, andb) holding the temperature for 30-60 min.