Tailor-made thermosets obtained by sequential dual-curing combining isocyanate-thiol and epoxy-thiol click reactions

Abstract

In this work, a new family of thermosets based on thiol-isocyanate-epoxy networks has been prepared via sequential dual-curing methodology where both reactions are activated by temperature. The sequential dual behaviour of the new system proposed here is based on the faster reaction kinetic of the first curing stage, i.e. the isocyanate-thiol coupling, which proceeds at a relatively low temperature, compared to the second stage, i.e. the epoxy-thiol reaction, between the remaining thiol functionalities and the epoxy groups that takes place at a higher temperature. Furthermore, the effect of using different aliphatic isocyanates was investigated. Both reactions have a click character and the intermediate/final materials show a wide range of properties depending on the relative contribution of both curing stages thanks to the selected ratio between the isocyanate and epoxy groups. The new thermosets obtained were characterized from the thermal and dynamic mechanical point of view, resulting excellent candidates as smart materials due to their narrow transitions, which favours fast and controlled changes in their macromolecular features.