Metal catalyst-free and recyclable silicone elastomer

The global production of silicone is expected to reach 2.9 to 3.0 million tons in 2024, but only 35,000 to 45,000 tons are estimated to be recycled in the same year. There is, simply said, a lack of possibilities for recycling silicones. The subject has gained increasing attention over the last few years, with many interesting publications demonstrating the recycling of even crosslinked silicones. Most of the research is, however, focused on
depolymerization to monomers and cyclic polysiloxanes, which will require polymerization step(s) before reintroducing them into the material loop. A more facile strategy would instead be to selectively cleave the crosslinking points and, by doing so, retrieve the actual polymers with their functionalities. The polymers would then be ready for re-crosslinking without requiring further synthesis. In this work, this strategy is explored in the form of a silicone elastomer in which silyl ethers constitute the crosslinks.

The silyl ether crosslinked silicone elastomer is achieved by a metal catalyst-free curing of a carbinol end-functionalized silicone polymer with a polysilazane (PSz) crosslinker. Our experiments show that polymers with carbinol end-groups can be reclaimed after a low-energy intensive chemical recycling process. The recycling process relies on having a suitable solvent to swell the elastomer and a weak acid to hydrolyze the silyl ether crosslinks. The reclaimed polymers can be re-cured using new PSz to form new silicone elastomers. The recycling procedure is  illustrated in Figure 1