Facile synthesis of new optically active poly(amide–imide)s derived from N,N′-(pyromellitoyl)-bis-l-leucine diacid chloride and aromatic diamines under microwave irradiation

Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) was reacted with l-leucine (2) in a mixture of acetic acid and pyridine (3:2) and the resulting imide-acid [N,N′-(pyromellitoyl)-bis-l-leucine diacid] (4) was obtained in high yield. The compound (4) was converted to the N,N′-(pyromellitoyl)-bis-l-leucine diacid chloride (5) by reaction with thionyl chloride. A new facile and rapid polycondensation reaction of this diacid chloride (5) with several aromatic diamines such as 4,4′-diaminodiphenylsulfone (4,4′-sulfonyldianiline) (6a), 4,4′-diaminodiphenyl methane (6b), p-phenylenediamine (6c), m-phenylenediamine (6d), 2,4-diaminotoluene (6e) and benzidine (6f) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol. The polymerization reactions proceeded rapidly and are completed within 12 min, producing a series of optically active poly(amide–imide)s with good yield and moderate inherent viscosity of 0.28–0.46 dl/g. All of the above polymers were fully characterized by IR, elemental analyses and specific rotation. Some structural characterization and physical properties of these optically active poly(amide–imide)s are reported.