Microwave irradiation as a versatile tool for increasing reaction rates and yields in synthesis of optically active polyamides containing flexible l-leucine amino acid

In this investigation, a series of thermally stable and optically active polyamides (PA)s containing bulky pendant chiral functionality from polymerization of a diacid monomer containing rigid phthalimide and flexible l-leucine groups, (2S)-5-[4-(4-methyl-2-phthalimidylpentanoylamino)benzoylamino]isophthalic acid with several aromatic and aliphatic diisocyanates such as 4,4′-methylenebis(phenyl isocyanate), toluylene-2,4-diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate under gradual heating method were prepared and compared with microwave-assisted polycondensation method. The polymerization reactions occurred rapidly under microwave irradiation and produced a series of PAs with good yields and moderate inherent viscosities of 0.26–0.68 dL/g. All of the new PAs showed good solubility and were readily dissolved in aprotic organic solvents. The resulting polymers were characterized by FT-IR, ¹H NMR spectroscopy, and elemental analysis technique. Thermal stability and thermal properties of PAs were evaluated by thermogravimetric analysis and differential scanning calorimetry. The interpretation of kinetic parameters (E, ∆H, ∆S, and ∆G) of thermal decomposition stages have been evaluated using Coats–Redfern equations.