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Molten Salt as a Green Reaction Medium: Synthesis of Polyureas Containing 4-phenylurazole Moiety in the Main Chain in the Presence of Tetrabutylammonium bromide as an Ionic Liquid

Ionic Liquids (IL)s have been generating increased interest over the last decade. ILs were initially introduced as an alternative green reaction media because of their unique chemical and physical properties of nonvolatility, nonflammability, thermal stability, and controlled miscibility. The step-growth polymerization reactions of 4-phenylurazole (PHU) with various diisocyanates such as hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), and toluylene-2,4-diisocyanate (TDI) were performed in the presence of tetrabutylammonium bromide (TBAB) as a reaction medium with or without dibutyltin dilurate (DBTDL) as a catalyst. The polymerization reaction gave similar results in the presence or absence of DBTDL, indicating that, the catalyst is not needed in this process. The resulting polyureas showed high yields and moderate inherent viscosities in a range of 0.23-0.29 dL/g in N,N-dimethylformamide (DMF) at 25 °C and they are soluble in most polar aprotic organic solvents. This method was compared with the polymerization reaction in conventional solvent such as, N,N-dimethylacetamide (DMAc). In the case of using TBAB, higher yields and inherent viscosities were obtained. All of the above polymers were characterized by FT-IR and thermogravimetric analysis (TGA).