Polybenzimidazole (PBI) molecular weight and Mark‐Houwink equation

The molecular weight, and intrinsic viscosity of polybenzimidazole (PBI) and its phosphonylated derivatives are reported. The relationship between intrinsic viscosity [η] and weight average molecular weight (Mw) for PBI has been established in H2SO4 and DMF‐LiCl. The Mark Houwink constants Kw of 5.2 × 10−3 mL/g, α of 0.92 for H2SO4 solvent systems and, Kw of 3.2 × 10−2 mL/g, α of 0.754 for DMF‐LiCl solvent system have been determined at Mw < 65,000. The intrinsic viscosity of PBI determined by the Huggins–Kraemer method was compared with a single point method, and found that both methods fit well for PBI in relatively low concentration solvent system, giving ∼ 99% accuracy.