Fourier transform infrared study of supramolecular polyurethane networks containing pyridine moieties for shape memory materials

Non-covalent interactions are increasingly used in the molecular self-assembly of well-defined structures. In this study, a series of pyridine-containing polyurethanes (PUPys) were synthesized with diisocyanates and pyridine derivatives. Fourier transform infrared spectroscopy was employed to identify the vibration frequencies and investigate the relationship of shape memory effect (SME) and hydrogen-bonded supramolecular structure of the PUPys. The results show that a large fraction of strong hydrogen bonds are formed in the urethane group as well as in the pyridine ring. Moreover, the hydrogen bonding in the pyridine ring not only shows a response to a temperature stimulus in the PUPys, but is also responsive to moisture in N,N-bis(2-hydroxylethyl)isonicotinamine (BINA)/hexamethylene diisocyanate (HDI)-based PUPys; the hydrogen bonds in the urethane group have a higher dissociation temperature and show little response to moisture absorption. Accordingly, the PUPys are expected to show thermally induced and moisture-induced SMEs. Finally, the shape recovery process of films in the shape of flowers induced by temperature and moisture supports the idea that the PUPys could be used as thermally induced shape memory polymers (SMPs), and the BINA/HDI-based PUPys could be used as moisture-sensitive SMPs.