Selective Degradation of Polydimethylsiloxane (PDMS) Catalyzed by [Polydentate Ligand-Alkali Metal Fluoride] Complexes

Conventional base catalysts such as KOH often suffer from low yields and multiple side reactions in the degradation of polydimethylsiloxane (PDMS) to produce high-value dimethyl cyclosiloxane (DMC). To overcome these limitations, a novel supramolecular catalyst-[K(cryptand[2.2.2])]F-was designed and synthesized in this work by utilizing the coordination interaction between KF and cryptand[2.2.2]. In this structure, K⁺ forms a stable coordination bond with the cryptand, which effectively weakens the electrostatic interactions within KF, thereby significantly promoting the dissociation and nucleophilic reactivity of F⁻ in the organic phase and resulting in a highly efficient supramolecular catalytic system. The use of a DMSO/n-octadecyl alcohol mixed solvent not only facilitated a homogeneous reaction between PDMS and the catalyst but also reduced the solvation effect on F⁻, further enhancing its catalytic performance. Experimental results show that with only 1% [K(cryptand[2.2.2])]F loading, the cyclic monomer yield from PDMS cleavage reached 95%, with DMC selectivity exceeding 99.5%. Moreover, the catalyst retained high activity over ten consecutive cycles, maintaining a yield above 93% and demonstrating excellent stability. Additionally, an improved Dean-Stark trap was used to construct a continuous production system capable of synthesizing DMC under low solvent-circulation conditions. This study presents a new and efficient catalytic strategy for the green and high-value upcycling of silicone waste, offering promising prospects for advancing a circular economy in the silicone industry.