Full Circle Recycling of Polysiloxanes via Room-Temperature Fluoride-Catalyzed Depolymerization to Repolymerizable Cyclics

Siloxane-based polymeric materials are widely used all over the world because of their chemical, mechanical, and thermal stability and due to their low toxicity. Despite their usefulness, the high energy cost used to make them is lost when they are discarded, wasting resources and energy. Practical and simple methods of recycling these materials are therefore required. However, the simplification of these methods is underdeveloped. The present techniques used to recycle silicone-based materials, such as polydimethylsiloxanes, often involve high temperatures/pressures and complicated setups. To address this issue, we have established an efficient room-temperature technique for the depolymerization of silicone-based polymers, elastomers, and resins in the presence of low catalytic amounts of fluoride in specific high swell organic solvents. The products primarily contain cyclic siloxane units (D-4, D-5, and D-6) as verified by GCMS and Si-29 nuclear magnetic resonance. Nearly any silicone resin can be depolymerized rapidly using these methods. Silicone-rich systems result in the best conversions and the highest quantity of identifiable cyclics, while complex resins resulted in complicated products alongside discernible cyclics. We have also repolymerized the products from this process to reform silicones via acid, base, and fluoride catalysis. This process has the potential for large-scale industrial processing because of the use of mild conditions and solvent recycling ability.

Automated summary

Siloxane-based polymeric materials are widely used worldwide for their stability, but their high energy cost and lack of simple recycling methods are issues. The authors have developed a room-temperature depolymerization technique using low catalytic amounts of fluoride in organic solvents, showing potential for large-scale industrial processing.