STRUCTURAL STUDIES OF POLY(DIMETHYL-TETRATHIOPHENE, AN INTERMEDIATE BETWEEN POLY(THIOPHENE) AND POLY(3-METHYLTHIOPHENE)

Grignard coupling of 2-bromo-3-methylthiophene and 5,5'-dibromo-2,2'-d ithiophene, and chemical polymerization of the resulting tetramer usin g FeCl3 as coupling agent gave a new type of substituted polythiophene , namely ''-dimethyl-(2,2':5',2'':5'',2''')tetrathiophene)) (PDMTT), w ith two new and interesting features compared to conventional polythio phenes. Firstly, we have a polythiophene with exact methyl side group positioning, eliminating the possibility of side group position disord er. Secondly, and especially interesting from a structural point of vi ew, we obtained a polymer which is intermediate between the unsubstitu ted polythiophene (PT) and poly(3 methylthiophene) (P3MT). The polymer was obtained as a black insoluble powder which turned out to be amorp hous. X-ray diffraction profiles were measured and compared to the pro files of PT and P3MT. We were able to follow the intensity and positio n variation of the diffraction peaks as a function of the methyl subst itution.