Researchers at Belgium's Ghent University (www.ugent.be/en) have discovered a new method that allows the reversible conversion of a thermoset polymer into a thermoplastic. The “click chemistry” conversion is achieved when triazolinediones (TADs) react with the electron-rich molecules of unsaturated organic compounds, including polyurethane, for example. This characteristic enables them to cross-link the polymer chains, thereby creating a thermosetting polymer with macromolecular crosslinks.

The researchers said the cross-linking reaction can take place under ambient conditions, adding that the TADs are insensitive to moisture and air and do not require a catalyst to react. Thanks to their reaction kinetics and relatively low energy barriers, the TADs are capable of breaking and forming reaction bonds easily, with the “click” reaction happening at room temperature, while the “unclick” can be brought about at a temperature of 120°C – provided that the reaction partner includes an indole group.

These characteristics mean a thermoset material can be re-cast or extruded, while maintaining the properties of a thermoset polymer during its use. Another bonus of the “click chemistry” process is that the unreacted TAD molecules have a bright red colour that disappears during the reaction, allowing the user to directly ascertain that the process has occurred.