Safe and fast polyamidation of 5-[4-(2-phthalimidiyl-propanoylamino)benzoylamino]-isophthalic acid with aromatic diamines in ionic liquid under microwave irradiation
Ionic liquids are outstanding microwave-absorbing agents owing to their high ionic conductivity and polarizability, thus leading to a high heating rate and a considerably shortened reaction time. In this study, a series of novel optically active polyamides (PA)s with pendent 4-(2-phthalimidiyl-propanoylamino)benzamide units were prepared with excellent yields via a simple microwave heating method using 1,3-dipropylimidazolium bromide and triphenyl phosphite. In comparison with classical heating, microwave irradiation was demonstrated to be a more effective energy source. The resulting PAs have inherent viscosity in the range of 0.52–0.71 dL/g. All of the polymers were readily soluble in many organic solvents and showed good thermal stability associated with high glass-transition temperatures above 200 °C as measured by differential scanning calorimetry. Thermogravimetric analysis showed that the 10% weight-loss temperatures in nitrogen were 455 and 410 °C, a significant improvement in thermal stability having been observed with the increase in the side-chain length.