Proton NMR relaxation in highly conducting polyanilines

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Abstract
Measurements of the conductivity and proton spin-lattice relaxation times T1p and T1 in polyanilines (PANI) prepared through a novel polymerization-condensation synthesis are presented. The new method of preparation yields a significant increase in the electrical conductivity, which may be related to the lesser amount of decomposition products, leading to a more uniform distribution of dopant protons along the chain, thus allowing the charge carriers to move along a longer path. The effects of the increase of the effective length of the chains on the relaxation rates are studied in terms of their frequency and temperature dependences. From an analysis of the data in the light of a diffusion equation for the magnetization, it appears that the intra-chain diffusion rate is larger than that in conventional PANI, whereas the cut-off frequency calculated by comparing T1p and T1 gives an upper limiting value of the inter-chain diffusion rate of about 107 rad s-1.