The characteristics and mechanism of hydrogen bonding assembly in linear polyurethane with multiple pendant 2-ureido-4[1H]-pyrimidone units

2-Ureido-4[1 H ]-pyrimidone (UPy) can form strong quadruple hydrogen bonding (H-bonding) and is widely used to construct supramolecules. Though the H-bonding assembly of UPy-containing polymers has been widely reported, little attention is paid to the H-bonding characteristics and mechanism of UPy-containing polyurethanes. Here, by using UPy- p -PDLLA-SMPU, a linear polyurethane with multiple pendant UPy units as the model polymer, the H-bonding assembly characteristics in solution, solid film and melt are systematically investigated. It is found that the UPy units mainly exist as free monomers in DMSO, UPy dimers in CHCl 3 , and both free monomers and dimers in DMF. The dimerization of UPy can promote the H-bonding of urea and urethane groups and thus the formation of hard segment aggregates. Thereby, the thermal resistance and reversibility of the H-bonds are significantly enhanced in both UPy- p -PDLLA-SMPU film and melt. UPy- p -PDLLA-SMPU can transition from a rubber state (70°C–85°C) to a viscous flow state (≥120°C), presenting the characteristics of both chemically crosslinked and linear polyurethanes. This work provides a clear picture on the H-bonding assembly of UPy units together with urea and urethane groups in UPy- p -PDLLA-SMPU. The obtained assembly characteristics and mechanism are beneficial for the design and processing of UPy-based physically crosslinked polyurethanes.