Preparation and Characterization of Poly(thienylene)s

Abstract

Abstract Nickel compounds (NiCl2 and NiCl2(2,2′-bipyridine)) catalyze polycondensation of dihalothiophenes (2,5-dihalothiophenes, 2,4-dibromothiophene, and 3-methyl-2,5-dibromothiophene) by dehalogenation with magnesium to give the corresponding poly(thienylene) type polymers (poly(2,5-thienylene), poly(2,4-thienylene), and poly(3-methyl-2,5-thienylene)). Copolymerization of 2,5-dibromothiophene and 2,4-dibromothiophene affords copolymers formulated as (\llap–2,5-C4H2S) \llap–m(\llap–2,4-C4H2S) \llap–n. About 15 wt% of poly(2,5-thienylene) prepared in THF at 66 °C is soluble in CHCl3 at room temperature and the CHCl3-soluble fraction has a molecular weight of 1370. The remaining fraction is considered to have a higher molecular weight as judged from its physical properties. IR and 1H-NMR spectra of the polymers are consistent with the structures described above. The electronic spectra of poly(2,5-thienylene) and poly(3-methyl-2,5-thienylene) show large bathochromic shifts of the π-π* absorption bands from those of thiophene and 3-methylthiophene, respectively, indicating that π-electrons in these polymers are extensively delocalized along the polymer chains. In contrast to the electronic spectra of these polymers, that of poly(2,4-thienylene) shows only a minor shift of the π-π* absorption band from that of thiophene reflecting the less extensive π-electron delocalization along the polymer chain in the poly(2,4-thienylene). All the polymers are nonsensitive to air and have high thermal stabilities.