Poly temperature-independent Pauli

The analysis given in the previous sections assumes that at heavy doping concentrations, polyacetylene (and other conducting polymers) have the electronic structure of metals. Only in a few cases has this been checked in detail. For example, the existence of a temperature independent Pauli susceptibility has been established for polyacetylene and poly thiophene, indicative of a metallic system with a finite density of states at the Fermi surface. For poly aniline, a Pauli contribution to the susceptibility has been inferred, only dominates in the most ciystaUine material. 

ESR studies of poly(4,4 -methylenedianiline) [438] in its salt form showed evidence of thermally activated and temperature-independent Pauli-type paramagnetism, whereas the corresponding base form showed thermally activated Pauli- and Curie-Weiss-type paramagnetism. Charge transport was proposed to occur via polarons and bipolarons. With UV-vis spectroscopy performed ex situ at chemically prepared polymer samples, no evidence of... 

At least in heavily doped polymers, the temperature-independent susceptibility is obsci-vcd in PT and P3AT (poly(3-alkylthiophenc)) doped with AsF(, [255,279, 282] PFc," [282] SO.iCF.r [295] CIO - [282,296] and BFj" [258], except for PT/P3AT-1T [255,297]. Possible reasons why it is not obseiwed in PT/P3AT-Ij arc (1) the ESR linewidth from the Pauli spins is too broad to observe by ESR and (2) the charge transfer from iodine to polymer is insufficient to fill a band gap. The situation with these systems is similar to the case of PPy on the metallic electronic states the electrical conductivity reaches 500 S/cm [298-300], the small... 

The discovery 5 th when in solution in concentrated sulfuric acid, poly aniline is in the protonated form, [B-NH-B-NH-]+ n, and that it is recovered as the partially crystalline salt, [B-NH-B-NH-]+ n(HS04 )n, from solutions in sulfuric acid O y precipitation in water or methanol) has opened the way to a more complete characterization of the polymer, and to studies directed toward the determination of the intrinsic properties of the ordered material. For example, the temperature independence of the spin susceptibility of the more highly ordered crystalline material above 125K is consistent with the Pauli spin susceptibility expected for a metal,with a density of states at the Fermi level estimated as 1 state per eV per formula unit (two rings). 

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