Eco-friendly fast synthesis and thermal degradation of optically active polyamides under microwave accelerating conditions

An optically active bulky aromatic diacid chiral monomer, (2S)-4-(4-methyl-2-phthalimidylpentanoylamino) benzoylamino]isophthalic acid (1), containing a rigid phthalimide and flexible L-leucine pendent group was synthesized in five steps. A fast and clean method for direct polyamidation reaction of monomer 1 with various aromatic diamines under microwave irradiation and conventional heating was performed. The polymerization reactions provided optically active polyamides with high yields and inherent viscosities in the range of 0.36–0.74 dL/g. Their thermal properties were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry. TGA thermograms show that the polymers are thermally stable, 10% weight loss temperatures are in excess of 385°C, and char yields at 800°C are higher than 56%. The data obtained from TGA were used to study the kinetics of thermal decomposition of the resulting polymers. The interpretation of kinetic parameters (E, ΔH, ΔS and ΔG) of thermal decomposition stages was evaluated using Coats and Redfern equation.