Synthesis and Characterization of New Optically Active Poly(amide-imide)s Based on N,N′-(Pyromellitoyl)-bis-L-Amino Acids and 1,3,4-Oxadiazole Moieties

New optically active poly(amide-imide)s derived from chiral N,N′-(pyromellitoyl)-bis-L-amino acids (3a–f) and 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (BAO) (8) were synthesized by direct polycondensation. Chiral N,N′-(pyromellitoyl)-bis-L-amino acids were obtained by the reaction of pyromellitic dianhydride with two equimolar of L-alanine (2a), L-valine (2b), L-leucine (2c), L-isoleucine (2d), L-phenyl alanine (2e) and L-2-aminobutyric acid (2f) in acetic acid. The polycondensation reaction proceeded through the in situ formation of an Vilsmeier adduct by dissolving tosyl chloride (TsCl) in a mixed solvent of pyridine and DMF. The resulting thermally stable poly(amide-imide)s were obtained in good to high yields and inherent viscosities ranging between 0.31 and 0.55 dl/g. The structures of the new polymers were confirmed by elemental analysis and spectral methods (FT-IR, 1H-NMR). Optical activity and thermal behavior investigated by polarimetric measurements and thermogravimetric analysis, respectively.