The molecular weight of polyaniline by light scattering and gel permeation chromatography

Abstract

Polyaniline base in the emeraldine oxidation state displays strong absorption between 450 and 800 nm which precludes its use at these wavelengths for light scattering (LS) measurements. Therefore, as-synthesized polyaniline in the emeraldine base form was first reduced with hydrazine to polyaniline in the almost colorless leucoemeraldine oxidation state. Absolute weight average and number average molecular weights and polydispersity of the leucoemeraldine base by LS measurements were found to be 25 200, 11 560 and 2.18, respectively. However, the relative weight average molecular weight obtained by gel permeation chromatography of the emeraldine base, used to synthesize the leucoemeraldine base, was found to be ≈52 000 and that of emeraldine base obtained by the air oxidation of the above leucoemeraldine base was ≈36 800. Thus, subjecting emeraldine base to a cycle consisting of reduction with hydrazine followed by air oxidation results in significant chain scission and, hence, in a reduction of molecular weight. It is concluded that a lower limit of the number of ring-nitrogen units per polymer chain in the as-synthesized emeraldine base is 128.