Self-assembling unsymmetrical bis-ureas

Abstract

Model compounds of unsymmetrical bis-ureas have been designed and synthesised to investigate and further understand the formation of supramolecular polymer arrays. Association constants (<200M−1) for the bis-ureas have been determined by 1H 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.