Synthesis and characterization of neutral newly substituted polyalkylthiophenes

In this work, two newly substituted polyalkylthiophenes, poly(3,4-dihexyl-2,2'-bithiophene) and its didodecyl analogue have been prepared in order to compare their properties with those of the regioisomeric poly(3-alkylthiophene)s containing the same amount of head-to-tail configuration (conventional PATs). Remarkable differences between the material characteristics of these two kinds of polyalkylthiophene have been observed, thus enabling us to elucidate the side chains effects exclusively attributable to the difference between the side chains distribution along the polythiophene backbone. In the neutral bulk state, compared to that of the conventional PATs, the polymers prepared for this study have been found more thermostable materials exhibiting higher flexibility and less ordered (in the crystallographic sense) molecular assemblies, still able to afford an average conjugation length as long as that of the conventional PATs, but varying between wider limits. This seems to be closely connected with a lower degree of side chains interactions and/or the high proportion (50%) of unsubstituted thiophene rings. Based on these effects of molecular structure on the material properties at room temperature, we have anticipated in the novel polymers, at higher temperatures, the possibility of weaker thermochromism and better conductivity stability than in their regioisomeric conventional PATs. (C) 2000 Elsevier Science Ltd. All rights reserved.