Temperature dependences of the magnetic susceptibility of solutions and powders of polyaniline synthesized by oxidative polymerization using two methods were measured by ESR in the temperature range from 123 to 423 K. The dependences observed can be described by the integral of susceptibility of the polymer fragments in the triplet state over the singlet-triplet splitting from E 1 to E 2 with constant weight. The susceptibility of the fragments was accepted to obey the Bleaney-Bowers equation. The most part of the experimental dependences can be presented as the sum of the temperature independent susceptibility and the susceptibility obeying the Curie law. The both susceptibilities are described in a single manner at E 1 < 0. In some cases, the comparison of the calculated and experimental dependences makes it possible to determine the length of the fragments L. The conditions of polymer synthesis, heating, and water vapors affect the E 1 and E 2 values. A similar analysis can be applied to other conducting polymers. , and many other, are interesting due to their unusual physical prop erties and a possibility of their diverse practical use. From this point of view, the most attention was given to studies of luminescence and conductivity. Magnetic properties are of a special interest, being tightly related to the nature of charge carriers and to fine features of the polymer structure.The frequently observed experimental linear temperature dependence of the product of the magnetic susceptibility by the temperaturemakes it possible to divide the susceptibility into two com ponents: the temperature independent part χ P and the part obeying the Curie law χ = C/T (see, e.g., data for polyaniline, 1-3 polythiophene, 3 and polypyrrole 4 ). The origin of these two components is usually explained in terms of the "metallic" model, according to which pow ders and films of doped conducting polymers are highly ordered metallic regions immersed into amorphous re gions (see, e.g., Refs 1-3 and references cited therein). Paramagnetism and conductivity of conducting polymers are considered to appear after doping, i.e., when charges and unpaired electrons are formed in the polymers. Due to the spatial periodicity of the metallic regions, the energy spectrum of electrons has a zone character. The upper zone is partially filled, resulting in the appearance of such properties as high electron conductivity and the temperature independent Pauli susceptibility. Distortions in the lattice periodicity induce a minor number of local ized electrons, viz., polarons with the spin 1/2, whose susceptibility obeys the Curie law. However, some experimental facts does not obey this scheme. It is natural to expect that the ESR lines of the localized spins and metallic regions have different widths but, in the most cases, the ESR lines of the conducting polymers exhibit no superposition of the lines with differ ent widths. As a rule, the shape of the ESR lines in the line center is close to the Lorentzian one, and the descent on the wings is faster. ...

The temperature and field dependences of the magnetic moment of polyaniline powder doped by m cresol were measured by SQUID magnetometry in the temperature range 2-300 K at 1000 Oe and in the range 0-50000 Oe at 2 K, respectively. The field dependence is not described by the Brillouin function for spin 1/2, as is expected in the framework of a commonly accepted "metallic" model. Both dependences are quite correctly described by a "triplet" model using a distribution of singlet triplet splitting (E) with the density distribution function having a narrow peak near E = 0.Conducting polymers including polyaniline, poly acetylene, polythiophene, polypyrrole, poly(para phe nylene vinylene), etc. possess unusual physical properties and can be used in various fields. Practically, the empha sis is placed on the studies of their luminescence and conductivity. Investigations of the magnetic properties occupy a special position because these properties are intimately related to the nature of charge carriers and to subtle features of the polymer structure.Often, the experimentally observed linear dependence of the product of the paramagnetic susceptibility of con ducting polymers by the temperature (χT) on temperature(1) allows one to divide the magnetic susceptibility into two components, viz., the temperature independent component χ P and the component obeying the Curie law χ = C/T (see, e.g., the data for polyaniline and its derivatives, 1-4 poly(ethylenedioxythiophene), 1 and polypyrrole 5 ). The origin of these two components is usually explained within the framework of a "metallic" model, which treats doped conducting polymers (in the form of both powders and films) as highly ordered metallic domains "immersed" into amorphous domains. The metallic domains are asso ciated with the temperature independent component (the Pauli susceptibility) while defects in the amorphous domains are responsible for the Curie susceptibility.However, a number of experimental facts do not obey the pattern mentioned above. For instance, it is unclear why the EPR lines of metallic and amorphous domains characterized by different widths do not overlap. In addi tion, it is difficult to explain the frequently observed nonlinear dependences χT-T in the framework of the "metallic" model. We have proposed a "triplet" model for paramagnetic centers in conducting polymers. 6 According to this model, conducting polymers comprise relatively short periodic fragments with close values of the angles between neighboring ring planes. These fragments are separated from one another by abrupt changes in these angles, each fragment can be in the triplet or singlet state, and there is a number of fragment conformations, which leads to variation of the singlet triplet splitting (E) over a wide range. In this case, the magnetic susceptibility can be described by an integral of the Bleaney-Bowers equa tion over the E distribution. For some fragments, triplets lie lower than singlets; these fragments are responsible for the Curie like contribution to the magnetic su...

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