10.1039/b316913h
The research aims to selectively synthesize non-symmetrical bis-ureas and investigate their self-assembly properties. The study focuses on creating bis-ureas with one aromatic and one aliphatic group, which combine the solubility of aliphatic bis-ureas and the strong association of aromatic ones. The key chemicals used include various aromatic amines (such as 4-n-butylaniline and 2,6-diethylaniline), and aliphatic amines (like 2-ethylhexylamine). 2,4-toluene diisocyanate (2,4-TDI) plays a pivotal role as the core reactant for synthesizing mono-isocyanate/mono-ureas and subsequently non-symmetrical bis-ureas. The selective synthesis involves reacting an aromatic amine with an excess of 2,4-TDI to obtain mono-isocyanate/mono-ureas, which are then reacted with chosen amines to form the desired non-symmetrical bis-ureas. The synthesized compounds were characterized using techniques like 1H NMR, FTIR spectroscopy, and viscosimetry. The results show that non-symmetrical bis-ureas exhibit stronger self-assembly and better solubility compared to symmetrical bis-ureas. Additionally, bis-ureas grafted onto polydimethylsiloxanes (PDMS) form physical cross-links, leading to rubbery solids with promising rheological properties. The study concludes that the selective synthesis of non-symmetrical bis-ureas opens up new possibilities for creating materials with unique self-assembly and mechanical properties.
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