Novel Biobased Polyurethanes Synthesized from Nontoxic Phenolic Diol Containing l-Tyrosine Moiety Under Green Media

Ionic liquids (ILs) have been accepted as 'green' alternatives to the organic solvents in a range of synthesis, catalysis and electrochemistry, because of their distinctive chemical and physical properties. In this investigation, N,N'-(pyromellitoyl)-bis-l-tyrosine dimethyl ester as a chiral bioactive diphenolic monomer was prepared in three steps. The polycondensation of this monomer with various aromatic and aliphatic diisocyanates such as 4,4'-methylene-bis-(4-phenylisocyanate) (6a), toluylene-2,4-diisocyanate (6b), isophorone diisocyanate (6c) and hexamethylene diisocyanate (6d) were carried out in the presence of tetrabutylammonium bromide as a molten IL under microwave irradiation conditions and was compared with polymerization in traditional solvent like N-methyl-2-pyrrolidone. The results show that IL efficiently absorbs microwave energy, thus leading to a very high heating rate. Thus IL method is safe and green since toxic and volatile organic solvents were eliminated. All of the novel poly(urethane-imides) (PUIs) showed good solubility in various organic solvents. The obtained new polymers were characterized with FT-IR, H-1-NMR, elemental and thermogravimetric analysis techniques. Thermogravimetric analysis (TGA) of two representative PUIs demonstrated that they are rather thermally stable. In vitro toxicity studies showed that the synthetic materials are biologically active and they are nontoxic to microbial growth then could be classified as bioactive and biodegradable compounds.