Aniline Polymerization into Montmorillonite Clay: A Spectroscopic Investigation of the Intercalated Conducting Polymer

Abstract

The polymerization of aniline intercalated into montmorillonite clay was monitored by in situ UV−vis−NIR and resonance Raman spectroscopies and in situ small-angle X-ray scattering. In the initial stages of the polymerization, it is observed the PANI−ES polaronic band at 750 nm in the UV−vis−NIR spectrum and also the characteristic PANI-ES resonance Raman spectrum (excited at 632.8 nm), which indicate that the head-to-tail coupling reactions between anilinium radical cations are occurring. Nevertheless, the resonance Raman spectrum excited at 488.0 nm presents bands at 1211, 1370, 1455, and 1608 cm-1, assigned to the benzidine dication species, which suggests that tail-to-tail coupling reactions are also occurring. In the final stages of polymerization, the presence of electronic absorption bands at 670 and 620 nm indicates the formation of new chromophoric species, which is also confirmed by its peculiar resonance Raman spectrum at 632.8 nm wavelength. The in situ SAXS results show that, during the anilinium polymerization in aqueous clay suspension, the interlayer spacing is ca. 19 Å. XRD diffraction pattern and SEM images of the powder PANI−MMT nanocomposites indicate that the polymerization occurs mainly between the clay layers, and the basal spacing is ca. 13.2 Å. While the IR spectra of nanocomposites show only bands due to PANI−ES-like segments, resonance Raman and nitrogen XANES techniques lead to the presence of PANI−ES-like chains, benzidine segments, azo bonds, and phenazine-like rings in the structure of the confined conducting polymers. The XPS technique detects only PANI−ES segments of the polymeric structure, suggesting that on the external surface and/or on the edge of clay crystal they are predominant in the chains.