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

Abstract

Abstract2‐Ureido‐4[1H]‐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 CHCl3, 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.