Electron paramagnetic resonance conducting polymer

While spectroelectrochemical measurements provide energy levels of intermediate species generated from the polymer during electrolysis at different potentials, they do not offer much information on whether or not the species would have unpaired spins. Several groups of investigators conducted electron paramagnetic resonance (EPR) studies in an effort to explain the potential dependency of conductivities. 

There are various methods of the glass transition temperature evaluation based on temperature dependence of polymer physical properties in the interval of glass transition 1) specific volume of polymer at slow cooling (dilatometric method) 2) heat capacity (calorimetric method),3) refraction index (refractometric method) 4) mechanical properties 5) electrical properties (temperature dependence of electric conductivity) or maximum of dielectric loss 6) NMR ° 7) electronic paramagnetic resonance, etc. 

Rao and co-workers [82] used an inverted emulsion process for the synthesis of the emeraldine salt of PAM using a novel oxidising agent, benzoyl peroxide. The polymerisation was carried out in a non-polar solvent in the presence of four different protonic acids as dopants and an emulsifier (sodium lauryl sulfate). The polymer salts were characterised spectroscopically by ultraviolet-visible, Fourier-transform infrared, Fourier-transform Raman and electron paramagnetic resonance spectroscopy. Thermogravimetric analysis, was used to determine the stability of the salts and the activation energy for the degradation. The conductivity of the salts was found to be in the order of 10 S/cm. 

Polypyrrole was one of the earliest conducting polymers produced. In 1968 DalT-Olio et al. [2] oxidized pyrrole in aqueous sulfuric acid to obtain a powdery precipitate on a platinum electrode. Pyrrole black, as this material became known, had a conductivity of 8 S cm". Chemical analysis determined the presence of 75% poly pyrrole and 25% sulfate anions. An intense electron paramagnetic resonance signal indicated that the polymer possessed a large number of free spins and gave a g value of 2.0026 (comparable to that of a free electron, g = 2.0023). 

Electron paramagnetic resonance studies have been reported for these chelate polymers (7, 55) and utilized in discussions of structure. Electrical conductivities in the 10 -10 ohm i cm i range were obtained on some of these materials (55). 

Because of its high stability and its good electrical conductivity polypyrrole (PPy) can be used in many technical applications, e.g., in the field of microchips and microstructured electronic devices. Polypyrrole can also be used as a material in sensor technology. The interaction of different gases wifii the polymer structure can be detected by the paramagnetic resonance [1] or electrical conductivity measurements... 

In 1968/1969 DaH Olio et al. in Parma, Italy, revitalized polypyrrole chemistry by oxidizing pyrrole itself electrolytically to pyrrole black ("noir d oxypyrrol")/° In contrast to the investigations of Weiss et al., Dall Olio and his coauthors focused on the electrochemical behavior of pyrrole and its electropolymerization. The paramagnetic behavior of the polymer was studied (the g-factor of the free radical was measured to 2.0026 by electron spin resonance spectroscopy), and a remarkable electric conductivity of 7.54 S/cm at ambient temperature was foimd. 

---