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A new-type tetraimide-dicarboxylic acid (I) was synthesized starting from the ring-opening addition of p-aminobenzoic acid (p-ABA), 4,4'-oxydiphthalic anhydride (ODPA), and 4,4'-methylenedianiline (MDA) at a 2:2:1 molar ratio in N-methyl-2-pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of poly(amide-imide-imide)s ([III.sub.a-i]) with inherent viscosities of 0.78-1.45 dL/g was prepared by triphenyl phosphite-activated polycondensation from the tetraimide-diacid I with various aromatic diamines ([II.sub.a-i]) in a medium consisting of NMP, pyridine, and calcium chloride. Most of the polymers were readily soluble in a variety of organic solvents such as NMP. N,N-dimethyl acetamide, dimethyl sulfoxide, and even in less polar m-cresol. Compared with those of the corresponding poly(amide-imide)s [IV.sub.a-i], the solubilities of poly(amide-imide-imide)s [III.sub.a-i] were greatly improved. Polymers [III.sub.a-h] afforded tough, transparent, and flexible films, which had tensile stren gths ranging from 87 to 107 MPa, elongations at break from 9% to 14%, and initial moduli from 2.0 to 2.4 GPa. The glass transition temperatures of polymers were recorded at 270°C-309°C. They had 10% weight loss at temperatures in the range of 540°C-570°C and left more than 52% residue even at 800°C in nitrogen., INTRODUCTION Aromatic polyamides, a kind of polymer material with superior mechanical strength (1, 2), are synthesized from aromatic diamines and aromatic dicarboxylic acids. DuPont Kevlar® [poly(p-phenylene) terephthalamide] and DuPont Nomex® [...]