Polyurethane-urea hydrogen bonding

STRUCTURE 4.1 Hydrogen bonding in a hydroxyurethane. (Reprinted from E. Delebecq, J-P. Pascault, B. Boutevin, and F. Ganachaud, On the Versatility of Urethane/Urea Bonds Reversibility, Blocked Isocyanate, and Non-Isocyanate Polyurethane, Chem. Rev. 113 (2013) 80-118. With permission.)... 

The very polar urethane and urea groups and the very strong hydrogen bonding between these groups make polyurethanes very resistant to hydrocarbons and oils. This is one of the biggest advantages of PU elastomers over the conventional rubbers. 

Chemical recycling of polyurethanes by ammono-lytic cleavage of urethane and urea bonds under supercritical conditions has been described [48]. It is well known that a number of low-boiling materials give enhance solubility and reactivity under supercritical conditions. Ammonia has a critical point at 132.45°C and 112.8 bar (11.28 MPa) with a density of 0.235 g/cm. Being able to act as hydrogen-bond donor and acceptor, it provides good solubility for polyurethanes and... 

The contribution which the different types of polar groups make to the properties of polyurethane elastomers depends in part upon their ability to enter into strong hydrogen-bonded associations. The substituted urea linkage, formed by the reaction of an isocyanate with an amine, is regarded as exceptional in its contribution to the physical properties, and it is therefore a preferred component in many bulk elastomers where the structural irregularity introduced by the use of a non-symmetrical diisocyanate or polyol is compensated by the strong urea interactions. 

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