THE MOLECULAR-WEIGHT OF POLYANILINE BY LIGHT-SCATTERING AND GEL-PERMEATION CHROMATOGRAPHY

Polyaniline base in the emeraldine oxidation state displays strong abs orption between 450 and 800 nm which precludes its use at these wavele ngths for light scattering (LS) measurements. Therefore, as-synthesize d polyaniline in the emeraldine base form was first reduced with hydra zine to polyaniline in the almost colorless leucoemeraldine oxidation state. Absolute weight average and number average molecular weights an d polydispersity of the leucoemeraldine base by LS measurements were f ound to be 25 200, 11 560 and 2.18, respectively. However, the relativ e weight average molecular weight obtained by gel permeation chromatog raphy of the emeraldine base, used to synthesize the leucoemeraldine b ase, was found to be approximately 52 000 and that of emeraldine base obtained by the air oxidation of the above leucoemeraldine base was ap proximately 36 800. Thus, subjecting emeraldine base to a cycle consis ting of reduction with hydrazine followed by air oxidation results in significant chain scission and, hence, in a reduction of molecular wei ght. 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.