Two aromatic hyperbranched polyamines with s-triazine rings were synthesized from A(2) (4,4'-sulfonyl dianiline or 4,4'-methylene dianiline) and B-3 (2,4,6-trichloro-s-triazine) types of monomers by a single-step nucleophilic displacement polymerization technique in the presence of diisopropyl ethyl amine as the base. The hyperbranched polyamines were obtained in high yields (similar to 82-90%) with this technique. The polymers were characterized through solubility testing, measurements of the inherent viscosity, Fourier transform infrared, ultraviolet, H-1-NMR, and C-13-NMR spectroscopy, and X-ray diffraction studies. The inherent viscosities of the polymers were in the range of 0.23-0.42 dL/g in 0.5% (w/v) N,N'-dimethylacetamide at 27 +/- 0.1 degrees C. They were soluble only in highly polar solvents such as N,N'-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. The thermal behavior of the polymers was investigated with thermogravimetric analysis and differential scanning calorimetry studies. The flame-retardant characteristics of the polymers were tested through the measurement of the limiting oxygen index. In the thermogravimetric analysis of these hyperbranched polyamines, no weight loss was observed below 250 degrees C under a nitrogen atmosphere, whereas differential scanning calorimetry showed that the glass-transition temperatures were about 240 and 230 degrees C for the polymers with sulfonyl and methylene groups, respectively. (c) 2007 Wiley Periodicals, Inc.