A solid-state synthesis, mechanism, and characterization of high molecular weight poly (3-aminobenzenesulfonic acid) with FeCl 3 .6H 2 O as a binary oxidant and dopant

Abstract

The homopolymerization of o,m,p-aminobenzenesulfonic acid (o,m,p-ABS) has been a challenging act because of the strong electron withdrawing nature of the sulfonic acid group (-SO₃H). Therefore, polymerization was done by either sulfonating of polyaniline (PANI) or copolymerization of the corresponding monomers with aniline. In this study, we reported a novel method for the preparation of nanopolymer from m-ABS as monomer using FeCl₃.6H₂O as a binary oxidant and dopant agent in ratio of oxidant to the monomer equal to 5 ([Ox]/[M] = 5) in the solvent-free (solid-state) condition at 40–45 °C for 24 h and the yield of reaction was 46%. The polymer was characterized by a number of techniques such as Fourier transform infrared, ultraviolet-visible, atomic absorption, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, four probe conductimeter, and zeta potential. The morphology was determined by scanning electron microscopy, transmission electron microscopy and atomic force microscopy and particles size were found about 30–65 nm. The zeta potential by dynamic light scattering (DLS) at two concentrations of 0.20 g/l and 0.05 g/l was measured −61.7 mV and − 43.7 mV, respectively. It showed that the polymer has very good stability and it shows no coagulation and flocculation. The molecular weight was obtained by intrinsic viscosity [η], gel permeation chromatography, static light scattering (SLS) and DLS. The very high molecular weight was obtained by DLS, SLS and [η]. Mn and Mν were equal to 5200 kg/mol and 2173 kg/mol, respectively. The new mechanism based on para-head-to-tail polymerization was introduced explained poly (m-ABS) new structure containing Fe and the high molecular weight. This polymerization method was simple, effective and inexpensive, use of Lewis acid (FeCl₃) for both doping and oxidation, as well as resolving the need for high pressure and a long time for dialysis and has the merits of green and solvent-free (solid-state) condition. At the best of our knowledge, this report of polymerization of m-ABS is the most efficient method that has been reported so far.

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