The past two decades have seen extraordinary progress in synthesis and study of organic conjugated polymers and their nanocomposites. This caused by large prospects of utilization of such systems in molecular electronics and spintronics. One of the main scientific goals is to reinforce human brain with computer ability. However, a convenient modern computer technology is based on three-dimensional inorganic crystals, whereas human organism consists of biological systems of lower dimensionality. So, the combination of a future computer based on biopolymers with organic conjugated polymer semiconductors of close dimensionality is expected to increase considerably a power of human apprehension. This is why understanding the major factors determining specific spin charge transfer processes in conjugated polymers is now a hot topic in organic molecular science.

The charge in such systems is transferred by topological excitations, spin polarons and spinless bipolarons, characterized by high mobility along polymer chains. This stipulated the utilization of Electron Paramagnetic Resonance (EPR) spectroscopy as a unique direct tool for more efficient study and monitoring of spin reorganizing, relaxation and dynamics processes carrying out in polymer systems with such charge carriers. It was demonstrated that the method allows to obtain qualitative new information on spin-modified polymer objects and to solve various scientific problems.

The focus of the present Chapter is on the use of EPR technique in combination with the spin label and probe, steady-state microwave saturation, saturation transfer and conductometric methods in the study of initial and treated conjugated polymers. It covers a wide range of specific approaches suitable for analyzing of processes carrying out in polymer systems with paramagnetic adducts providing readers with background knowledge and results of the latest research in the field. It reviews the main experimental methodological approaches originally developed for the study of various organic condensed systems.

The Chapter is organized as following. The first part includes the fundamental properties of conjugated polymers with topological quasi-particles, polarons and bipolarons, as charge carriers. The second part is devoted to an original data obtained at X-band to D-band (30 ? 2-mm, 9.7 - 140 GHz) EPR study of the nature, relaxation and dynamics of polarons stabilized and initiated in widely used conjugated polymers and their nanocomposites. The third part reveals the possibility to handle of charge transport in some polymer composites with spin-spin exchange which can be used in the further creation of novel elements of molecular electronics and spintronics. Finally, theoretical and experimental background necessary for EPR study of the main magnetic resonance, relaxation and dynamics parameters of polaron quasi-particles in organic compounds are described shortly in the Appendix.