Electrochemical polymerization and depolymerization of 2,5-dimercapto-1,3,4-thiadiazole. QCM and spectroscopic analysis

Electrochemical oxidation of a dimercaptan, 2,5-dimercapto-1,3,4-thiadiazole (DMcT), to a polydisulfide (DMcT polymer) and electrochemical reduction of the polydisulfide at a carbon electrode and an indium - tin oxide electrode have been studied in 0.1 M LiClO₄ - acetonitrile by means of an in situ electrochemical quartz crystal microbalance and in situ spectroelectrochemistry, respectively. It is observed that the polymerization potential is more positive than the dimerization potential. Both the potentials at which DMcT dimer and DMcT polymer are formed are made more negative by the presence of a base. The potential at which the DMcT polymer is reductively depolymerized is also shifted in the negative direction in the presence of a base. The experiments also show that the DMcT polymer reacts with DMcT monomer under open-circuit conditions. This results in dissolution of the polymer in the presence of the monomer. The results also suggest that the product of the redox reaction is the DMcT dimer. Base is shown to hinder this reaction.