The influence of modification by nitric acid or chlorine on the regiospecific structure of poly(3-alkylthiophenes) (P3ATs)

The nitric and chloro derivatives of chemically synthesized poly(3-alkylthiophenes) (P3ATs) were obtained by chemical modification using chlorine (Cl2) or nitric acid (HNO3). On the basis of spectral analyses (UV-Vis, IR, 1H NMR), elemental analysis and gel permeation chromatography (GPC), it was observed that the nitric group (−NO2) was substituted in the 4- or 5-position of the thiophene ring of P3ATs. The −NO2 group substitution in the 4- or 5-position of the thiophene ring depends on the regiospecific structure of the P3AT polymer chains. The substitution in the 4-position takes place in the head-to-tail sequence diad in polymer chains. The substitution of −NO2 in the 5-position occurs in the head-to-head diad sequences and causes the degradation of the polymer chains. The modification of P3ATs by Cl2 causes the substitution of the chlorine atom in the 4-position of the thiophene ring and in the β-position of the alkyl group. The chlorine substitution in the 4-position of the thiophene ring does not depend on the regiospecific structure of the polymer; however, the chlorine substitution in the β-position of the alkyl group takes place in the head-to-head diad sequences. Moreover, the modification of P3ATs using chlorine does not cause the polymer chain degradation.