New optically active poly(amide‐imide)s based on N,N′‐(pyromellitoyl)‐bis‐L‐amino acid and 1,3‐bis(4‐aminophenoxy) propane: Synthesis and characterization

Five new poly(amide‐imide)s 8a–e were synthesized through the direct polycondensation reaction of five chiral N,N′‐(pyromellitoyl)‐bis‐L‐amino acids 3a–e with 1,3‐bis(4‐aminophenoxy) propane 7 in a medium consisting of N‐methyl‐2‐pyrrolidone, triphenyl phosfite, calcium chloride, and pyridine. The polycondensation reaction produced a series of novel poly(amide‐imide)s containing trimethylene moiety in the main chain in high yield with inherent viscosities between 0.34 and 0.65 dL/g. The resulted polymers were fully characterized by means of FTIR spectroscopy, elemental analyses, inherent viscosity, and solubility tests. Thermal properties of these polymers were investigated by using thermal gravimetric analysis (TGA) and differential thermal gravimetric (DTG). All of the polymers were soluble at room temperature in polar solvents such as N,N‐dimethyl acetamide, N,N‐dimethyl formamide, dimethyl sulfoxide, and N‐methyl‐2‐pyrrolidone. N,N′‐(pyromellitoyl)‐bis‐L‐amino acids 3a–e were prepared in quantitative yields by the condensation reaction of pyromellitic dianhydride (1,2,4,5‐benzenetetracarboxylic acid 1,2,4,5‐dianhydide) 1 with L‐alanine 2a, L‐valine 2b, L‐leucine 2c, L‐isoleucine 2d, and L‐phenyl alanine 2e in acetic acid. Also 1,3‐bis(4‐aminophenoxy) propane 7 was synthesized by using a two‐step reaction. At first 1,3‐bis(4‐nitrophenoxy) propane 6 was prepared from the reaction of 4‐nitrophenol 4 with 1,3‐dibromoprapane 5 in NaOH solution. Then, dinitro compound 6 was reduced by using Na2S.