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

Abstract

Silicones are ubiquitous materials owing to their exceptional mechanical and thermal stability as well as low toxicity. Recycling them has become a seducing target for Circular Economy purposes. Conventional chemical recycling processes of polysiloxanes allow for the recovery of valuable cyclic monomers. Unfortunately, they lack efficiency and still require high operating temperatures thus yielding detrimental by-products. We introduce an efficient method for the solvent-free depolymerisation of linear polydimethylsiloxanes using a [polydentate ligand-silanolate] complex as a catalyst, that promote 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 temperature (60°C-170°C) to efficiently yield of a mixture of cyclosiloxanes (up to 98-99% yield) from up to a 100g scale of waste silicone oils. Moreover, the recyclability of this catalyst was demonstrated over five runs without loss of activity.