Supramolecularly Reinforced Films from Polyurethane–Urea Dispersions Containing the Tris-Urea Motif

Because of the drive toward more green and sustainable processes for polymer synthesis, there is a growing desire to avoid solvent-borne polymer systems where possible and exchange for waterborne alternatives. Here, it isdemonstrated that the use of carbohydrazide as a chain extender of polyurethane prepolymers dispersed in water leads to the generation of polyurethane–urea dispersions that are supramolecularly reinforced by the tris-urea motif. Despite being incorporated as a small percentage of the total formulation by weight, films cast from polyurethane–urea dispersions that incorporate the tris-urea motif allow for more than an order of magnitude increase in Young’s modulus and an order of magnitude increase in tensile strength without any compromise in the elongation at break. It is also demonstrated that the tris-urea group provides better mechanical strength than a chemically cross-linked structure and also undergoes stress relaxation on a longer time scale. Furthermore, DMTA measurements demonstrate that the increased strength of supramolecular hydrogen bonding interactions increase the mechanical stability at elevated temperatures. The improvement in mechanical properties shown by tris-urea containing polyurethane–urea dispersions should allow for the use of waterborne systems where previously only solvent-borne polymers have been used.