Conducting polymers containing heterocyclic units

Electrically conductive films can be formed on electrode surfaces by electrochemical oxidation of solutions of heterocyclic compounds in electrolytes similar materials can sometimes be obtained by the use of conventional chemical oxidizing agents. Most of the work carried out on such materials appears to have been concerned with their properties rather than their structure consequently, there is often some uncertainty concerning exactly what these materials really are, a situation which leaves room for both imaginative speculation and argument. 

The most likely mechanism for the electrochemical polymerizations seems to be an initial formation of radical cations which then undergo dimerization with the loss of two protons. This initial dimerization will occur at or near the 

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Perhaps one of the best known syntheses of a heterocyclic polymer via the modification method is the generation of nitrogen-containing ladder polymers by pyrolysis of polyacrylonitrile) (77MI11109). The thermolysis is known to take place in discrete steps. The first step in the sequence, which can take place with explosive violence if the heating rate is not sufficiently slow, occurs at about 150 °C and can be detected by the onset of intense color formation. The product of this reaction (Scheme 101) is the cyclic tetrahydropyridine ladder structure (209). The next step, which is conducted in the presence of air at ca. 250 °C, involves the thermooxidation of polymer (209) to form what is best described as terpolymer (210) containing dihydropyridine, pyridone and pyridine units. 

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