Influência de diferentes ácidos dopantes nas propriedades estruturais, morfológicas, térmicas e elétricas da Poli(m-anisidina)

Abstract

Intrinsic Conductive Polymers (ICP) have been extremely studied due to the great possibilities of nanotechnological applications, and to the need to understand their properties so that these applications can be made feasible. The present research aims to synthesize poly(m-anisidine) (PMA) using different dopants to obtain the polymers PMA/HCl, PMA/HNO3 and PMA/H2SO4. X-Ray Diffraction (XRD), Structural Refinement using the Le Bail Method, Fourier-transforms Infrared Spectroscopy (FTIR), Spectroscopy in the Ultraviolet and Visible Regions (UV-vis), Scanning Electron Microscopy (SEM), Thermal Analysis (TG / DTA) and Electrical Conductivity measurements were performed to characterize the synthesized polymers. Additionally, using the Density Functional Theory (DFT) it was possible to correlate theoretical results with experimental ones. The XRD analysis showed the semi-crystalline patterns of PMA for all dopants used. The XRD patters were used to estimate the percentage of crystallinity by the method of deconvolution of the diffraction peaks, which were found around (30 ± 2) %. The FTIR technique allowed to verify stretches of the presence of the substituent in the meta position of the aromatic ring and of the doping counterions for each polymer. From the UV-VIS spectra, the energy gap values were estimated, as well as the main electronic transitions. The results of TG/DTA showed the greater thermal stability of the polymer PMA/H2SO4, indicating that the strong bonds caused by the sulfoxide groups of the dopant result in thermal degradation and heat release at temperatures higher than those observed for the other polymers. SEM images indicated that polymers tend to form spheres. The refinements by the Le Bail method allowed to evidence the influence of the counterions volumes in the polymeric structure: the direction [010] presented the highest value for PMA/H2SO4 due to the incorporation of the respective counterion in the molecular structure. Accordingly, the largest unit cell volume (1173.9 Å 3) presented by the same polymer was verified. For the other polymers, the cell parameters were proportional to the counterion volumes (in the [010] direction) and also to the molecule size (in the [001] direction). The shape of the PMA/HNO3 crystallite indicated spherical crystal growth in the [001] x [010] directions, while the PMA/H2SO4 showed greater growth in the directions influenced by the presence of the counterions, [100] x [010]. The DFT analysis showed a greater reduction in the Fermi level for PMA/H2SO4, with an almost null gap, equivalent to PMA/HNO3 in the creation of new states below the Fermi level, as well as a greater contribution in the electronic density caused by oxygen atoms. PMA/H2SO4 showed the highest conductivity value (8.34 x 10-7 S.cm-1), justifying the lowest gap value. This work is expected to contribute to the provision of structural, morphological, thermal, electrical, and theoretical information about the poly(m-anisidine) polymer not yet available in the scientific literature.