Effect of the polydispersity on electrochemical properties in solution of poly(N-alkylcarbazole)s

Poly(N-alkylcarbazole) synthesized from the corresponding 3,6 dihalide mono mer using zerovalent nickel as a catalyst has an average value for its poly dispersity of ca. 2. The electrochemical behaviour in solution is character ized by as many signals as weight populations in the crude sample. We have prepared, by selective solubilization in acetone, various samples having a low polydispersity tinder lower than 1.4) and studied their electrochemical properties when these compounds are solubilized in dichloromethane. We obs erved that the electrochemical behaviour of these samples with low polydisp ersity is much better defined than the crude samples but less well-defined than the only carbazole oligomer having a well-defined structure easily ava ilable, i.e. the 9,9'-diethyl 3,3' dicarbazyle. These results allow the stu dy of the variation of the apparent diffusion coefficient versus the averag e molecular weight M-n. Finally, we show that the decrease of electrochemic al activity of poly(N-alkylcarbazole) having a low polydispersity deposited as a thin layer on platinum as a function of the number of electrochemical cycles is less pronounced compared with a film of the crude product. Furth ermore, this decrease is also less pronounced with higher molecular weight fractions. Thus, a decrease in the polydispersity as well as an increase in the molecular weight of the polymer may be helpful in the improvement of t he life time of electrochromic devices. (C) 2000 Elsevier Science Ltd. All rights reserved.