We report the synthesis and characterization of a kinetically controlled, thermoreversible supramolecular polyurethane whose mechanical properties depend unusually strongly on the processing history. Materials were prepared by solution casting, quenching and annealing of quenched material, allowing pronounced micro-structural evolution, which leads to rapid increases in modulus as determined by rheological analysis. Tensile tests showed that the quenched material is soft, weak and ductile (shear modulus ~ 5 MPa, elongation ~ 250 %), but after annealing, at 70 °C for one hour, it becomes stiffer, stronger and more brittle (~ 20 MPa, ~ 20 %). FTIR and NMR spectroscopic analysis, coupled with MDSC and SAXS, were performed to investigate the network's dynamic structural changes. SAXS results suggest the presence of a lamellar structure in the sample when solution cast at high temperature, or annealed. This ordering is unique when compared to structurally-related supramolecular bisurethane and bisurea polymers, and may be the cause of the observed path dependence. These mechanical properties, which can be switched repeatedly by simple thermal treatments, coupled with its adhesion properties as determined from peel and tack tests, make it an excellent candidate as a recyclable material for adhesives and coatings.

and Hayes, W. (2016) A systematic study of the effect of the hard endgroup composition on the microphase separation, thermal and mechanical properties of supramolecular polyurethanes. Polymer, 107. pp. 368378.

We report the design, synthesis and assessment of the first examples of self-immolative systems triggered by reactive non-acidic electrophilic agents such as alkyl or benzylic halides.

Model compounds of unsymmetrical bis-ureas have been designed and synthesised to investigate and further understand the formation of supramolecular polymer arrays. Association constants (< 200 M-1) for the bis-ureas have been determined by 1 H NMR spectroscopy, and further characterised by optical spectroscopy. In addition, SAXS analysis of the bulk material reveals the formation of different highly ordered structures demonstrating complex hydrogen bonding of these unsymmetrical materials. Thermal transitions are also observed in some examples of unsymmetrical bis-ureas near to the melting point, as evidenced by double endotherms in DSC analysis. We also propose a re-organisation mechanism whereby the supramolecular array is first altered before proceeding to melt which is supported by variable temperature SAXS analysis.