Development of thiourethanes as robust, reprocessable networks

In this letter, we present a robust covalent adaptable network (CAN) that relies on dynamic, exchangeable thiourethanes. A primary aliphatic isocyanate, hexamethylene diisocyanate (HDI), and a primary aliphatic thiol, ethoxylated-trimethylolpropane tri(3-mercaptopropionate) (EETMP), are employed to form a network that can fully relieve an applied stress at 90 °C in under 40 min through the thiourethane bond exchange with a low loading (1 mol%) of catalyst, 1,5-diazabicyclo[4.3.0]non-5-ene (DBN). Based on the kinetic behavior of the dynamic chemistry, and as monitored via real-time FT-IR, synergetic dissociation and association mechanisms of the thiourethane bond exchange are proposed to explain the higher catalyst efficiency of the combined basic and nucleophilic catalyst, DBN, as compared to the strong basic catalyst, potassium tert-butoxide, and the strong nucleophilic catalyst, N-hetero carbene. Moreover, this thiourethane network exhibits excellent reprocessablity under relatively mild conditions (110 °C), which makes it a promising potential alternative to urethane materials in industry.