Intrinsic viscosity measurement of dilute emeraldine base solutions for estimating the weight average molecular weight of polyaniline

Aggregation of the emeraldine base (EB) form of polyaniline in dilute solution is a major problem, which prevents full understanding of the colligative and hydrodynamic properties of this polymer. However, when 2-methylaziridine (2MA) is added to a polar aprotic solvent, EB readily dissolves without aggregation. The reduced viscosities of dilute N-methyl-2-pyrrolidinone (NMP) solutions containing EB are linear functions of EB concentration in the presence of 2MA. The Mark-Houwink coefficients (alpha = 0.77, and K = 1.2 x 10(-4)) for the EB/NMP/2MA system were determined by correlating their weight average molecular weight (M,) values, determined by gel-permeation chromatography (GPC) relative to polystyrene standards, with their measured intrinsic viscosity values ([eta]). The M, of any unknown EB sample may be reliably estimated by first measuring the sample's intrinsic viscosity, and then applying these a and K values with the Mark-Houwink equation.