Selective synthesis of non-symmetrical bis-ureas and their self-assembly

Symmetrical bis- ureas composed of two urea functions linked together by a toluene ring were previously shown to form long supramolecular polymers and thus highly visco- elastic solutions, thanks to cooperative self- assembly involving four hydrogen bonds. In this paper, we report the direct and selective synthesis of non- symmetrical bis- ureas. Mono- isocyanate/ mono- ureas were first obtained from a one- step selective reaction between one aromatic amine and one isocyanate function of 2,4- toluene diisocyanate. Then, non-symmetrical bis- ureas, tetra- ureas, and bis- urea functional polydimethylsiloxanes ( PDMS) were obtained by reacting the mono- isocyanate/ mono- ureas with well chosen amines. The chloroform solutions of these compounds were characterised by quantitative FTIR spectroscopy and viscosimetry. It was shown that non-symmetrical bis- ureas substituted on one side by an aromatic moiety and on the other by an aliphatic group combine the solubility of aliphatic bis- ureas and the strong association of aromatic ones. Moreover, the association of bis- ureas grafted onto polydimethylsiloxanes is efficient and leads to the physical cross- linking of these polymers, even in chloroform.