Polyamides from isophthaloyl chloride and 1,3-diamino-4-chlorobenzene with diverse constitutional order were obtained in a one-stage synthesis varying the polymerization temperature and the monomer mixing modes. The constitutional order was calculated by H-1 and C-13 NMR spectroscopies. A model to determine the constitutional isomerism in these polycondensates was applied with the relevant kinetic reaction parameters obtained from the model reactions. The Monte Carlo technique was used to model the constitution along the polycondensation reaction as a function of the average polymerization degree. Constitution was determined by kinetic factors and not by thermodynamic ones. (C) 2003 Wiley Periodicals, Inc.