This study focused on the crystallization promotion of poly(trimethylene terephthalate) (PTT), with an aim at engineering thermoplastics applications. The effects of organic sodium (Na) salts, including Na stearate, Na benzoate, disodium-p-phenolsulfonate (2Na-p-PS), disodium-p-hydroxybenzoate (2Na-p-HB), and the sodium ionomer of poly(ethylene-co-methacrylic acid) (Na-EMAA), were investigated as nucleating chemical agents with differential scanning calorimetry and capillary viscometry. For comparison, the effect of fine talc powder was also examined. The chemical agents were generally more effective than fine talc powder. Na stearate and Na benzoate caused large-scale decomposition of PTT. 2Na-p-PS was quite thermally stable and caused little decomposition. 2Na-p-HB was the most efficacious of the nucleating chemical agents and caused mild decomposition. Na-EMAA was the most thermally stable and induced an increase in melt viscosity. A remarkable improvement in the crystallization rate of PTT was successfully attained at a minimum polymer decomposition cost by the introduction of a suitable amount of 2Na-p-PS, 2Na-p-HB, or Na-EMAA or by the concurrent proper incorporation of both of the latter two agents. (C) 2004 Wiley Periodicals, Inc.