ELECTROCHEMICAL AND CHEMICAL SYNTHESES OF POLY(THIOPHENES) CONTAINING OLIGO(OXYETHYLENE) SUBSTITUENTS

A comparative analysis of the solubility, structure, and properties of chemically and electrochemically synthesized poly[3-(3,6-dioxaheptyl)thiophene] (PDHT) has been carried out. Whereas 50% of the chemically prepared polymer (polyC) is soluble in chloroform, the solubility of the electrosynthesized polymer (polyE) is limited to 20%. H-1 NMR spectra of the soluble polymers show that polyC contains a large number of irregular alpha-beta' and/or beta-beta' linkage defects and ca. 40% head-to-head (HH) coupling. In contrast, the structure of polyE seems to involve essentially alpha-alpha' and head-to-tail(HT) linkages. Cyclic voltammetry (CV) of solution-cast films shows that the CV of polyE is strongly reminiscent of that of directly electrodeposited PDHT, while that of polyC lacks the double-redox system characteristic of PDHT, and reveals a ca. 250 mV higher oxidation potential. Electronic absorption spectra of solutions and solution-cast polymer films confirm that polyE is more conjugated than polyC and that both soluble polymers are much less conjugated than electrodeposited PDHT. The considerable differences observed in the stereo- and regioselectivity of the chemical and electrochemical syntheses are discussed with regard to the particular structure of the monomer in relation with the specificity of the two synthetic methods.