Six new poly(amide-imide)s 8a-f containing trimethylene moiety in the main chain were synthesized by the polycondensation reactions of 1,3-bis[4,4'-(trimellitimido) phenoxy] propane 6 with six different aromatic diamines 7a-f in a medium constituting N-methyl-2-pyrrolidone, triphenylphosphite, CaCl2, and pyridine as condensing agents. The polycondensation reaction produced a series of novel poly(amide-imide)s 8a-f in high yields with inherent viscosities between 0.35 and 0.63 dL/g. The resulting poly(amide-imide)s were characterized by elemental analysis, viscosity measurements, thermal gravimetric analysis (TGA and DTG), solubility tests, and nu spectroscopy. 1,3-Bis[4,4'-(trimellitimido) phenoxy] propane 6 as a new monomer containing trimethylene moiety was synthesized using a three-step reaction. At first 1,3-bis[4,4'-nitrophenoxy] propane 3 was prepared by the reaction of 4-nitrophenol 1 with 1,3-dibromo propane 2 in DMF solution. Then, dinitro 3 was reduced to 1,3-bis[4,4'-aminophenoxy] propane 4 by using a solution of sodium sulfite in ethanol. Finally, 1,3-bis[4,4'-(trimellitimido) phenoxy] propane 6 was prepared by the reaction of one equivalent diamine 4 with two equivalents of trimellitic anhydride 5 in a mixture of acetic acid-pyridine (3 : 2). (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3293-3299, 2010