University of Surrey: New plastic turns into a gas when heated – then reforms once cooled

Researchers at the University of Surrey have developed a polymer that breaks down into gaseous monomers at just 90°C and spontaneously recombines into the original solid polymer upon cooling. The material could enable new approaches to chemically recyclable plastics as well as coatings that can be applied and thermally removed. The findings were published in the journal "Macromolecules".

The material is poly(1,2-dithiolane), also known as poly(trimethylene disulfide). The researchers produced the polymer through radical and cationic ring-opening polymerization of 1,2-dithiolane. According to the university, the resulting material is soft, insoluble and hydrophobic, giving it properties that are in some respects comparable to polyethylene.

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The key difference lies in its thermal behavior. When heated to 90°C, poly(1,2-dithiolane) efficiently depolymerizes into its monomers. At this temperature, the monomers are gaseous. Upon cooling, they polymerize again without any additional chemical processing step, forming a solid, water-repellent polymer with its original properties. The process can be repeated.

This distinguishes the approach from many chemically recyclable polymers investigated to date. According to the University of Surrey, these often require temperatures of around 150 to 200°C for depolymerization. In addition, recovered monomers frequently have to be processed separately and then repolymerized. With the new material, by contrast, depolymerization, evaporation and subsequent polymer formation are driven by changes in temperature.

The researchers demonstrated three potential applications. Polymer vapor was condensed onto surfaces to create water-repellent coatings. These layers could subsequently be removed by reheating. In addition, contaminated polymer was separated from a model additive by sublimation and then recovered as a purified solid.

The scientists see particular potential for coatings on geometrically complex surfaces, where liquid coating systems may reach their limits. The process also demonstrates a possible route for purifying and reusing appropriately designed polymer materials.

The researchers regard the work primarily as a proof of concept for a new class of circular materials. The polymer is not intended as an immediate replacement for conventional commodity plastics. Further research will investigate, among other things, how the chemistry can be tailored to achieve different material properties and applications.

The study, "Lipoic Acid Without the Side Chain: Sublimable Homopolymers and Degradable Copolymers Based on 1,2-Dithiolane", was conducted by Touseef Kazmi and other researchers led by Peter J. Roth at the University of Surrey. It was published in "Macromolecules" under DOI 10.1021/acs.macromol.6c01500.

More information: www.surrey.ac.uk

University of Surrey, Guildford, Großbritannien

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