New plastic vaporizes when heated, then reforms upon cooling

A plastic that can disappear into a vapour when gently heated and then rebuild itself as a solid when cooled has been developed by scientists at the University of Surrey, offering a striking new model for how recyclable materials could be designed. Unlike conventional plastics, which are engineered to resist heat and chemical change, the new polymer can repeatedly switch between a solid coating and a gaseous form at comparatively low temperatures. The researchers say the discovery is not a replacement for polyethylene or a complete answer to the global plastic-waste crisis, but it demonstrates a previously unavailable strategy for creating materials that can be applied, removed, purified and reused with far fewer processing steps.

The material is based on a class of sulfur-containing molecules known as 1,2-dithiolanes. The Surrey team’s study, published in Macromolecules, investigates polymers made from a specially designed lipoic-acid-derived building block, described in the paper as “lipoic acid without the side chain.” In polymer chemistry, small molecular units called monomers are joined through chemical reactions to create long chains. Those chains determine whether a material behaves like a soft film, a rigid solid, a rubber or a liquid. In this case, the monomer’s strained five-membered disulfide ring gives the polymer unusual chemical reversibility, allowing the long chains to break apart and reform under controlled conditions.

Most everyday plastics are valuable precisely because their molecular structures are difficult to disrupt. Polyethylene, used in carrier bags, food packaging and shampoo bottles, consists of stable carbon–carbon backbones that do not readily return to their original building blocks. Mechanical recycling can turn such plastics into lower-quality products, but chemical recycling is more demanding because the polymer must be broken down and the resulting compounds often require purification and further chemical processing. Even many polymers designed for chemical recycling need temperatures of approximately 150 to 200 degrees Celsius before depolymerisation becomes efficient. The Surrey material follows a different path, breaking down at about 90 degrees Celsius and producing a vapour rather than a liquid mixture of recovered monomers.

Depolymerisation is the reverse of polymerisation: instead of joining monomers into long molecular chains, it separates those chains back into their constituent units. When the Surrey polymer is heated, the bonds connecting the repeating 1,2-dithiolane-derived units can undergo a reversible ring-opening and ring-closing process. The polymer therefore loses its large-chain structure and converts into small molecules with sufficient volatility to enter the gas phase. As the vapour cools, the molecules condense and spontaneously polymerise, rebuilding the original material. This behaviour resembles sublimation and deposition more closely than conventional melt processing, because the polymer can move directly between a solid surface and a vapour without first passing through an ordinary liquid state.

That physical transformation could make the material particularly useful as a coating. To demonstrate the concept, the researchers generated a vapour from the polymer and allowed it to condense onto a surface, forming a continuous waterproof layer. Vapour deposition can reach areas that are difficult to cover with conventional liquid coatings, including intricate geometries, narrow gaps and textured surfaces. Liquid paints and protective films may pool, drain or leave uncovered regions when applied to complex objects. A vapour, by contrast, can travel across a surface before condensing, potentially producing a more uniform film. The resulting coating retained the soft, insoluble and hydrophobic characteristics associated with the polymer.

The same process can also remove the coating without solvents or aggressive chemical treatments. When the coated object is reheated to around 90 degrees Celsius, the polymer evaporates from the surface and can, in principle, be captured for reuse. This reversibility could be valuable in manufacturing, electronics, laboratory equipment and other applications where a temporary waterproof or protective layer is needed. A coating might be applied during fabrication, removed during repair, or recovered when a product reaches the end of its useful life. The approach could reduce the need for solvent-based stripping, although the researchers emphasise that practical systems would still need to address energy use, vapour containment, coating thickness and large-scale recovery.

The team also tested whether the polymer could be purified through its unusual phase change. In a model experiment, the material was deliberately contaminated with an additive. Heating caused the polymer to enter the vapour phase while the non-volatile contaminant remained behind. When the vapour cooled, it re-formed as a clean solid. This is a form of purification by sublimation, in which differences in volatility separate one substance from another. Conventional recycling often produces complex mixtures containing dyes, plasticisers, fillers, stabilisers and residues from previous use. The ability to separate a polymer from certain additives without transforming it through multiple liquid chemical stages could provide a useful foundation for future recycling technologies, although the method’s effectiveness will depend on the nature of the contaminant.

The scientists caution that the discovery remains a proof of concept rather than a ready-made industrial solution. A practical replacement for commodity plastics would need to match their low cost, mechanical strength, durability, production volume and resistance to environmental exposure. It would also need to be assessed over many heating and cooling cycles to determine whether the monomer, polymer or coating gradually degrades. Life-cycle studies would be required to compare the energy needed for low-temperature depolymerisation and vapour recovery with the energy used in conventional manufacturing and recycling. Nevertheless, the material’s combination of hydrophobicity, softness, reversibility and relatively low processing temperature suggests that its greatest value may lie not in replacing every plastic, but in inspiring specialised circular materials designed from the outset to be temporary, recoverable and chemically reusable.

The University of Surrey researchers describe the work as the introduction of a new design principle for polymer science: instead of making plastics permanently stable and then struggling to dispose of them, scientists could engineer materials whose stability is deliberately switchable. Touseef Kazmi, the study’s lead author, said the team had demonstrated a principle that was not previously available, while corresponding author Peter Roth said the chemistry could inspire a new generation of circular materials. The next challenge will be tailoring the molecular structure to control properties such as strength, flexibility, evaporation rate and re-polymerisation speed. If those obstacles can be overcome, plastics that vanish into recoverable vapour and return as the same material could turn a dramatic laboratory demonstration into a new route for cleaner coatings, easier maintenance and more precise polymer recycling.

Subject of Research: Reversible, sublimable polymers based on 1,2-dithiolane chemistry for low-temperature depolymerisation, vapour deposition, removable waterproof coatings and polymer purification.

Article Title: Lipoic Acid Without the Side Chain: Sublimable Homopolymers and Degradable Copolymers Based on 1,2-Dithiolane

News Publication Date: 11 August 2026

Web References: https://doi.org/10.1021/acs.macromol.6c01500

References: University of Surrey study published in Macromolecules, DOI: 10.1021/acs.macromol.6c01500

Keywords

Recyclable plastics, polymer chemistry, sublimable polymers, depolymerisation, 1,2-dithiolane, lipoic acid, vapour deposition, waterproof coatings, chemical recycling, circular materials, materials science