A novel benzimidazole-containing phthalonitrile monomer (BIPN) was synthesized. The chemical structure of BIPN was confirmed by various spectroscopic techniques. Differential scanning calorimetry measurement revealed that the self-promoted polymerization reaction of the BIPN proceeds extremely sluggish and showed low polymerization exothermic effect. Subsequent rheological measurement displayed that the BIPN was able to keep a stable and low melt viscosity for 4 h at 300 degrees C, 2 h at 310 degrees C, and 50 min at 330 degrees C. The derived BIPN polymers showed excellent thermal properties revealed by thermogravimetric analysis, which were better than those of the corresponding polymer derived from phthalonitrile monomer without benzimidazole moiety. IR analysis confirmed the occurrence of the triazine ring within the polymer crosslinking sites. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 4977-4982, 2012