Head-to-Tail and Head-to-Head Molecular Chains of Poly(p-Anisidine): Combined Experimental and Theoretical Evaluation

Abstract

Poly(p-anisidine) (PPA) is a polyaniline derivative presenting a methoxy (–OCH3) group at the para position of the phenyl ring. Considering the important role of conjugated polymers in novel technological applications, a systematic, combined experimental and theoretical investigation was performed to obtain more insight into the crystallization process of PPA. Conventional oxidative polymerization of p-anisidine monomer was based on a central composite rotational design (CCRD). The effects of the concentration of the monomer, ammonium persulfate (APS), and HCl on the percentage of crystallinity were considered. Several experimental techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), multifractal analysis, Nuclear Magnetic Resonance (13C NMR), Fourier-transform Infrared spectroscopy (FTIR), and complex impedance spectroscopy analysis, in addition to Density Functional Theory (DFT), were employed to perform a systematic investigation of PPA. The experimental treatments resulted in different crystal structures with a percentage of crystallinity ranging from (29.2 ± 0.6)% (PPA1HT) to (55.1 ± 0.2)% (PPA16HT-HH). A broad halo in the PPA16HT-HH pattern from 2θ = 10.0–30.0° suggested a reduced crystallinity. Needle and globular-particle morphologies were observed in both samples; the needle morphology might have been related to the crystalline contribution. A multifractal analysis showed that the PPA surface became more complex when the crystallinity was reduced. The proposed molecular structures of PPA were supported by the high-resolution 13C NMR results, allowing us to access the percentage of head-to-tail (HT) and head-to-head (HH) molecular structures. When comparing the calculated and experimental FTIR spectra, the most pronounced changes were observed in ν(C–H), ν(N–H), ν(C–O), and ν(C–N–C) due to the influence of counterions on the polymer backbone as well as the different mechanisms of polymerization. Finally, a significant difference in the electrical conductivity was observed in the range of 1.00 × 10−9 S.cm−1 and 3.90 × 10−14 S.cm−1, respectively, for PPA1HT and PPA16HT-HH.

Interfacing poly(p-anisidine) with photosystem I for the fabrication of photoactive composite films

“…In polymeric materials, similar functional moieties in different stereochemical and compositional environments experience distinctive chemical environments, thereby inducing variations in the chemical shis of various 1 H nuclei. 34 As a result, the spectrum of a polymer can exhibit overlapping neighboring signals with a similar spectral prole, as observed in the 1 H NMR spectrum of PPA in Fig. 2.…”

“…Rodrigues de Oliveira et al observed that the ratio of monomer to oxidant had a signicant effect on polymer structure and pellet conductivity. 34 ATR-FTIR spectroscopy was used to compare the IR peaks of the p-anisidine (PA) monomer vs. the PPA polymer, and to further validate a successful polymerization. Fig.…”

“…The absorbance peak at 1250 cm −1 for PPA is attributed to ν (C–O–CH 3 ), which exhibits a slight shift from that same bond frequency that is reported in literature and identified for p -anisidine at 1235 cm −1 . 34,42 PPA-specific bonds are identified at 1490 cm −1 and 1560 cm −1 for CC benzenoid and CC quinoid, respectively, with these bonds only appearing when repeat units are present. 34,35 The ratio of the quinoid and benzenoid in the polymer reveals a comparable ubiquity of these bonds in the polymer backbone.…”

“…34,42 PPA-specific bonds are identified at 1490 cm −1 and 1560 cm −1 for CC benzenoid and CC quinoid, respectively, with these bonds only appearing when repeat units are present. 34,35 The ratio of the quinoid and benzenoid in the polymer reveals a comparable ubiquity of these bonds in the polymer backbone.…”

“…32,33 The efforts of Rathidevi et al and Rodrigues de Oliveira et al are noteworthy, as they focused on the pristine polymer's oxidative chemical synthesis and characterization. 34,35 While Rathidevi et al mainly targeted a PPA-ZnO nanocomposite, they reported multiple characterization techniques for the polymer itself, whereas Rodrigues de Oliveira et al examined the polymer's morphology, conductivity, and crystalline structure by considering the effect of varying concentrations of oxidant (ammonium persulfate) and dopant (HCl) on the resulting crystalline structure of PPA via chemical oxidation of p-anisidine. Rodrigues de Oliveira et al reported that the chemical synthesis yielded a mixture of polymer structures, with varying proportions based on the synthesis conditions, where the C-N bonds that form during polymerization occur at the carbon either in the ortho or in the meta position of the repeating structure.…”