Study On Quadruple Hydrogen-Bonding Recognition Polyurethane

In recent years, the hydrogen bonding recognition supramolecular materials based on UPy (2-ureido-4[1H]-pyrimidone) unit have gained much attention. The UPy units could dimerize through quadruple hydrogen bonding recognition. The formation of the dimer could increase the apparent molecular weight. Apart from this, the properties of the supramolecular could be changed significantly. If several UPy units were introduced to one molecular chain, a supramolecular network could be formed in which UPy dimers acted as physical crosslinkers. Compared with the traditional chemical crosslinked network, this supramolecular network was reversible. While maintaining the elasticity, such polymers also enhanced its mechanical properties and improved its processability. For these reasons, the applications of the materials were widely enlarged.In this paper, a UPy functional group-containing diol was synthesized referring to former work. And then the UPy-containing polyurethane was achieved with PEG acting as the soft segment, UPy-containing diol and HDI as the hard segment. Its properties was studied through comparison with UPy-free polyurethanes. Viscosity test results showed that the UPy group can only associate in nonpolar solvent, such as CHCl₃. The association greatly improved the intrinsic viscosity. The tensile property tests indicated the improvement of tensile strength for the quadruple hydrogen bonding interaction. The glass transition temperature was increased due to the decline of the chain flexibility. The introduction of the ureido sacrificed the thermostability of polyurethanes. But the initial decomposing temperature was still above 250oC, which was acceptable. The crystallization of PEG was restricted by the interaction of quadruple hydrogen bonding.A series of PEG with different molecular weight was adopted to synthesize polyurethane samples with different content of UPy. The content and density of UPy had much influence on the properties of polyurethanes. The lower PEG molecular weight, the greater the density of UPy, the more remarkable the influence. The TEM images shows that, as the length of the soft segment increased, the morphology changes from fibrous to spherical.Finally, we selected the UPy-containing polyurethane with PEG10000 as the soft segment to study on its electrospinning properties. We mainly studied two factors: the ratio of solvent and the concentration. The results indicated the ratio of DMF/CHCl₃=1/1 was the best one. The applicable concentration of the spinning solution was 8%¹2%.