Synthetic Metals, 55-57 (1993) 1221-1226 122 1 THE ROUTES TOWARDS PROCESSIBLE AND STABLE CONDUCTING POLY(THIOPHENE)S O. PEI, 0. INGANJi, S, G. GUSTAFSSON$ AND M. GRANSTROM Laboratory of Applied Physics, Dept. of Physics, IFM, LinkSping University, S-581 83, Link6ping, Sweden SUNIAX Corp., 5357 Overpass Road, Santa Barbara, CA 93111, USA M. ANDERSSON, T. HJERTBERG£ AND O. WENNERSTROM Dept. of Organic Chem. and £Polymer Techn., Chalmers University of Technology S-412 96, GSteborg, Sweden J.E. OSTERHOLM, J. LAAKSO AND H. J,i~RVINEN Neste Oy Research Center, Kulloo, SF-06850, Finland ABSTRACT The underlying nature of the thermal instability of doped poly(3- alkylthiophene)s, a fatal problem for their application, is discussed. The so-called "thermal undoping" is attributed to interactions due to steric hindrance of the long flexible side chains, which twist the conjugated main chain and kick out the dopants. Thus the routes to suppress thermal undoping are to avoid or alleviate the side chain interactions by separating the side chains from each other, or from the main chains, and also leaving space around the main chains to accommodate dopants. Accordingly, poly(3-(4-octylphenyl)thiophene), random copolymers of 3- methylthiophene and 3-octylthiophene, and regular copolymers of thiophene and 3- octylthiophene are prepared. Thermal undoping is significantly suppressed in these polymers. Some of these polymers are soluble and fusible in the neutral state. After doping they become highly conductive, yet remain stable even at elevated temperatures. Thermochromism, solvatochromism and thermal undoping are thus all related to side chain mobility. INTRODUCTION Conducting polymers are usually intractable due to the rigid conjugated main chains. Many efforts have been made in the search for processible conducting polymers[l]. One major advance in recent years is the solubilization of 0379-6779/93/$6.00 © 1993 - Elsevier Sequoia. All rights reserved