Easy-to-make polymer stretches, sticks, self-heals

A few commercially available reagents and a little heat are all that’s needed to make a polymeric material that’s easily processed, highly stretchable, self-healing, and sticky, according to a study (Sci. Adv. 2018, DOI: 10.1126/sciadv.aat8192). The polymer may prove useful in producing adhesives, self-healing materials, and wearable devices. To make the compound, researchers at East China University of Science & Technology, including Da-Hui Qu, Yi-Tao Long, and chemistry Nobel laureate Ben L. Feringa, heated thioctic acid (TA), a coenzyme involved in animal metabolism, to 70 °C. The mild heat melts the organosulfur compound and triggers polymerization by opening TA’s five-membered ring at the site of a S–S bond. Cooling leads to poly(TA), a transparent solid cross-linked through carboxylic acid hydrogen bonds. But poly(TA) is metastable. So the researchers added diisopropenylbenzene (DIB) and ferric chloride to molten TA. Those reagents stabilize the product, poly(TA-DIB-Fe), by cross-linking it in three different ways (shown)—via hydrogen bonds, covalent bonds with DIB, and iron-carboxylate coordinative bonds. The polymer’s knack for repeatedly making and breaking three types of bonds endows it with many of its properties, such as the ability to be stretched to 150 times its original length without breaking.