Copolymers of 2-methoxyaniline with 2- and 3-aminobenzenesulfonic and 2- and 3-aminobenzoic acids: Relationships between the polymerization conditions, structure, spectroscopic characteristics and conductivity
Abstract
The effect of the reaction conditions - feed monomer ratio, oxidant/monomers ratio, reaction time, reaction temperature, T, and HCl concentration - on the structure, conductivity and spectra of partly self-doped copolymers of 2-methoxyaniline (OMA) with the anilinic acids. (ANIA) 2- and 3-aminobenzoic and the 2- and 3-aminobenzenesulfonic acids was studied using ICP-AES/elemental analysis, size exclusion chromatography, NMR, FT-IR, UV-vis and impedance spectroscopy. The molar fraction of the OMA units, F1, in a P(OMA/ANIA) copolymer always exceeded the OMA fraction, f1, in the feed monomer mixture since the OMA is much more reactive than any ANIA due to the electron-donating effect of the methoxy group.
Increasing f1 consistently increased the yield and the molecular weight (MW) of the P(OMA/ANIA), and with an under-stoichiometric amount of oxidant or a shortened reaction time this favored the incorporation of the OMA into the copolymer chains. Increasing the acidity of the reaction mixture increased the yield, MW and F1 of the P(OMA/ANIA)s, while increasing T gave just the opposite effects.
The unusual decrease in the yield (reaction rate) with an increase in the T was related to the increased population of low-reactivity ANIA units at the growing-chain-end positions. The electrical conductivity, , of the P(OMA/ANIA)s lies in the region typical for semiconductors (0.05-2.5 mS/cm) and is roughly an exponential growth function of F1 that differs significantly for P(OMA/ANIA)s with sulfonic and carboxylic groups.
In contrast, a conjoint correlation for all P(OMA/ANIA)s was found between and the relative intensity of the UV/vis Q-band. The decrease in with the increasing fraction of ANIA units in the P(OMA/ANIA) is in accord with the electrostatic binding of positive polarons and bipolarons (electronic charge carries) with immobilized counter-anions