A new approach to the mechanism of polymerisation of oligovinylthiophene

The electrochemical properties of the monomers 5-vinyl-2,2':5',2 " -terthiophene and 5-ethyl-5 " -vinyl-2,2':5',2 " -terthiophene and their electropolymerisation products have been studied by cyclic voltammetry, quartz microbalance and in situ conductivity measurements. Experimental parameters like scan rate or temperature have been varied. As the comparison of both substances shows, they do not polymerise along the vinyl group to form a comb-like polymer. They couple at the thiophene end of the monomer and undergo cross linking processes rather than chain propagation. A strong memory effect is observed. All the findings support the view that the latter one is based on the intermediate formation of 'sigma -dimers' which are stable in the charged state but slowly decay after discharging of the polymer. (C) 2001 Elsevier Science Ltd. All rights reserved.