Eight new flame-retardant poly(amide-imide)s with high inherent viscosities containing phosphine oxide moieties in main chain were synthesized from the polycondensation reaction of N,N'-(3,3'-diphenylphenylphosphine oxide) bistrimellitimide diacid chloride 7, with eight;aromatic diamine 8a-h by two different methods such as solution and microwave-assisted poly condensation. Results showed that the microwave-assisted polycondensation by using a domestic microwave oven proceeded rapidly, compared with solution potycondensation and were completed within about 10-12 min. The resulting poly(amide-imide)s 9a-h showed high thermal stability and flame-retardant properties. All of the obtained polymers were fully characterized by means of elemental analysis, viscosity measurements, solubility test, and FTIR spectroscopy. Thermal Properties of the PAIs 9a-h were investigated by using thermal gravimetric analysis (TGA), derivative thermogravimetric analysis (DTG), and differential scanning calorimetry (DSC). Char yield measurements at 600 degrees C demonstrated that incorporating phosphine oxide moieties in polymer backbone markedly improves their flame retardancy. All of the earlier polymers were soluble at room temperature in various organic solvents such as NMP, DMF, DMSO, DMAc, and concentrated sulfuric acid. (c) 2006 Wiley Periodicals, Inc.