Polyurea-Urethane Supramolecular Thermo-Reversible Networks

Novel polyurea-urethane (PUU) supramolecular polymer networks based on triuret and tetrauret blocks were synthesized. The network formation was controlled through the conformation of hydrogen bonding moieties and their concentration. FTIR spectroscopy and solubility tests showed the presence of significant hydrogen bonds only in triuret moieties and that these bonds conducted to cross-linked materials at room temperature. Hydrogen bonding association constant, K-assn = 95 M-1, was calculated using H-1 NMR for triuret blocks' self-associations. Dynamic mechanical analysis confirmed that triuret blocks conduct to a network at room temperature and that decross-linking occurs between 105 and 135 degrees C. The tetrauret blocks had a folded conformation at room and relatively low temperatures. The polymers containing these moieties did not cross-link at room temperature and below. Temperature increase favored unfolded conformation and conducted to intermolecular hydrogen bonds and, at high temperature, to cross-linked materials.