Back-to-cyclic monomers: chemical recycling of silicone waste using a [polydentate ligand-potassium silanolate] complex

Silicones are ubiquitous materials owing to their exceptional mechanical and thermal stability as well as low toxicity. Recycling them has become a relevant target for circular economy purposes. Conventional processes of chemically recycling polysiloxanes allow for the recovery of valuable cyclic monomers. Unfortunately, they lack efficiency and still require high operating temperatures, thus yielding detrimental by-products. Herein, we introduce an efficient method for the solvent-free depolymerisation of linear polydimethylsiloxanes using a [polydentate ligand-potassium silanolate] complex as a catalyst that promotes the chemical recycling of silicones into cyclic monomers from many industrial substrates including actual waste materials. Our method only requires a small amount of catalyst (0.1 mol%) and proceeds over a wide range of temperatures (60 degrees C-170 degrees C) to efficiently yield a mixture of cyclosiloxanes (up to 98-99% yield) from up to a 100 g scale of waste silicone oils. Moreover, the recyclability of this catalyst was demonstrated over five runs without loss of activity.