Polyaniline synthesis with iron(III) chloride-hydrogen peroxide catalyst system: Reaction course and polymer structure study
Abstract
We report on the catalytic polymerization of aniline (ANI) with FeCl(3)/H(2)O(2) system, which can considerably lower contamination of neat polyanilines (PANIs) by side-products characteristic of stoichiometric polymerization. However, catalytically prepared PANIs exhibit reduced conductivity related most probably to side reactions involving radicals generated as integral components of the FeCl(3)/H(2)O(2) system.
Catalytic polymerization of ANI with FeCl(3)/H(2)O(2) system was found to be the reaction of approximately 2nd order with respect to ANI and gives PANIs of a good quality only when [H(2)O(2)] in the reaction mixture was kept low, i.e., at under-stoichiometric ratios [H(2)O(2)]/[ANI]. At over-stoichiometric ratio [H(2)O(2)]/[ANI], PANIs of lowered conductivity, worse spectroscopic characteristics and increased size of PANI nanostructures were obtained; nevertheless, these PANIs were not over-oxidized to pernigraniline state.
The reaction-time profiles of the open-circuit potential of reaction mixtures exhibited an inflection related to the H(2)O(2) depletion from the system. Total consumption of H(2)O(2) exceeded its consumption necessary on AM polymerization, which proves partial decomposition of H(2)O(2) by Fe ions.
UV/vis and resonance Raman spectra indicate incomplete deprotonization of PANIs prepared with FeCl(3)/H(2)O(2) system and subsequently treated with aqueous ammonia, which proves partial self-doping of these PANIs. However, IR and NMR spectra indicate rather low extent of self-doping.
It has been proposed that self-doping of PANI involves phenolic OH groups originated from side reactions involving radical species formed from H(2)O(2).