N-trimellitylimido-L-methionine (3) was prepared by reaction of trimellitic anhydride (1) with -L-methionine (2) in acetic acid solution at refluxing temperature. This diacid was reacted with thionyl chloride, and N-trimellitylimido-L-methionine diacid chloride (4) was obtained in quantitative yield. The resulting diacid chloride was reacted with p-aminobenzoic acid in dry acetone and bis(p-aminobenzoic acid)-N-trimellitylimido-L-methionine (5) was obtained as a novel optically active amide-imide diacid monomer in high yield. The direct polycondensation of amide-imide diacidmonomer 3 with several aromatic diamines was carried out with tosyl chloride (TsCl)/pyridine(Py)/dimetheylformamide (DMF) system. The resulting thermally stable poly(amideimide)s (PAIs) were obtained in good yields and inherent viscosities ranging between 0.24 and 0.46 dL g(-1) and were characterized with FTIR, H-1 NMR, CHN, and TGA techniques. (c) 2007 Wiley Periodicals, Inc.