Diels-Alder thermoresponsive networks based on high maleimide-functionalized urethane prepolymers

Thermoreversible polyurethane networks were successfully prepared by DielsAlder reaction using a highly maleimide-functionalized urethane prepolymer with an epoxy-based furan coupling agent or a furan-functionalized polyurethane. Highly functional maleimide prepolymers with various functionalities were synthesized by the isocyanate-alcohol reaction from glycerol, H12MDI, and protected N-hydroxymethylmaleimide. Thermal behavior and de-crosslinking of the networks were studied via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and solubility tests. Swelling tests allowed the evaluation of the networks' density. Thermal properties and crosslinking density were influenced by furan and maleimide functionalities and by the nature of the diene. Denser networks with lower de-crosslinking temperatures were obtained using the epoxy-based furan coupling agent. With the furan-functionalized polyurethanes, looser networks and higher de-crosslinking temperatures were obtained. These higher de-crosslinking temperatures were attributed to the presence of more physical links in the networks.