Microwave-induced synthesis of chiral polyamides containing phthalimide, L-alanine and benzamide linkages

An aromatic optically active dicarboxylic acid monomer, 5-[4-(2-phthalimidiylpropanoylamino)benzoylamino] isophthalic acid was prepared in five steps in high yield and purity. A series of organosoluble, thermally stable and optically active polyamides (PA)s containing pendent groups of phthalimide, L-alanine and benzamide have been successfully synthesized under microwave irradiation. Excellent yields and very short reaction time were the main characteristics of this method. The same polymerization reactions were also carried out by conventional thermal heating and the results are compared. The resulting PAs had inherent viscosity in the range of 0.30-0.51 dL g-1. All of the these polymers are readily dissolved in various solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide and N,N-dimethylformamide. Thermogravimetric analysis demonstrated that the 10% weight-loss temperatures in nitrogen were 378 and 394 °C for selected two PAs. All of these polymers showed optical rotation which is due to successful insertion of L-alanine in the structure of chiral diacid monomer.