Abstract The ester–amide exchange reaction between poly(ethylene terephthalate) and p ‐phenylenediamine in n ‐dodecylbenzene as a solvent in the absence of catalyst was carried out to obtain heat‐resistant polyamide. The observation of the amide group generated in the reaction product was made by FTIR analysis and the relative extent of reaction was estimated by the amidation ratio from FTIR and the nitrogen content determined from elemental analysis. The effect of chemical structure in the homologous series of aliphatic and aromatic diamines on the reactivity of ester–amide exchange reaction was studied. How reaction variables such as time, temperature, and the amount of diamine used affected the extent of reaction and the heat‐resistant property of polyamide obtained was thoroughly studied. Finally, a search for an efficient catalyst among metal acetates was attempted. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2502–2512, 2004