Chemical oxidative polymerization of 4-amino-3-hydroxynaphthalene-1- sulfonic acid and its salts

Abstract

New functional homopolymeric, semiconducting materials soluble in polar solvents, were synthesized by chemical oxidative polymerization of 4-amino-3-hydroxynaphthalene-lsulfonic acid (AHNSA) and its salts, using ammonium peroxydisulfate as an oxidant, in water at room temperature. Polymerization products obtained from AHNSA, AHNSA hydrochloride, AHNSA mono-sodium salt and AHNSA di-sodium salt were characterized by elemental analysis, gel-permeation chromatography (GPC), infrared spectroscopy (IR) and conductivity measurements. Polymers of AHNSA salts have increased weight-average molecular weights and polydispersity index values, compared to AHNSA polymer. Molecular weights approach a maximum value of ∼25200 for polymers of AHNSA salts. Elemental analysis data of polymeric samples show a decrease of the S/C ratio for all polymeric materials in comparison with the monomer, indicating considerable elimination of sulfonic acid group from the macromolecular structure during the polymerization process. New substitution patterns shown by IR spectroscopic analysis combined with MNDO-PM3 semi-empirical quantum mechanical calculations revealed N - C coupling reactions as dominant, where C belongs to unsubstituted AHNSA ring. Coupling mode N - Ci is also important. Naphthoquinonoid and benzenoid structures were observed by IR spectroscopy. Influence of pH on the AHNSA oxidative chemical polymerization mechanism was examined.