Metal Catalyst-Free and Recyclable Silicone Elastomer Achieved Through Curing of a Carbinol-Functional Polydimethylsiloxane With a Polysilazane

Abstract

Both producers and end-users of silicone elastomers are facing a significant challenge regarding efficient recycling processes for their materials. The inherently stable nature of silicone elastomers gives them unique properties, but complicates their reentry to a circular material loop. This paper presents a recyclable silicone elastomer with crosslinks constituted by silyl ethers. Condensation curing of carbinol-functional polydimethylsiloxane (PDMS) with polysilazane (PSz) is proven to create a stable silicone elastomer without the need for a metal catalyst. The mechanical properties can be easily tuned by the addition of fillers as well as by chain extension. Adding the cured silicone elastomer to a solution of 0.055 mol L⁻¹ acetic acid (AcOH) in tetrahydrofuran (THF) for 24 h at 40°C yields a liquid silicone with a high resemblance to the starting polymer, demonstrating a selective cleavage of the silyl ether crosslinks. Experiments show that this reclaimed silicone can successfully be recured using new PSz to form new silicone elastomers. Mechanical properties similar to the starting elastomer are achieved when the reclaimed silicone is cured with pristine polymer in a 1:1 ratio, demonstrating the potential for industrial applications, where cured production scrap could be reintroduced to new elastomers via a simple process.