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

Abstract

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.