*3.5. FTIR Spectroscopy*

The chemical structure of the polyaniline, polyacrylonitrile, and obtained fibers was determined on the basis of infrared spectroscopy (Figure 5). A description of the characteristic vibrations is shown in Table 2 [15,25].

On the fibers' FTIR spectra, the bands characteristic of polyaniline and polyacrylonitrile were visible. In the case of PAN/PANI blended fibers, all absorption bands characteristic of polyacrylonitrile were clearly visible.

In the case of PAN/PANI blended fibers, all absorption bands characteristic of polyacrylonitrile were clearly visible at 3445, 2926, 2243, 1731, 1615, 1453 and 1250 cm<sup>−</sup>1. The peaks corresponded to N–H stretching and C–H stretching in the polymer structure, stretching in C≡N, stretching in C=O, stretching in C=C, bending C–H in CH2, and stretching in C–N. The gentle absorption bands characteristic of PANI were also visible at 1588, 1160 and 804 cm<sup>−</sup>1, which were characteristic of C=C stretching in the quinoid rings, C–N bond stretching in quinoid and benzenoid rings, and δ C–H in 1,2,4 trisubstituted benzene rings. FTIR analysis indicated that these fibers were composed of polyacrylonitrile and had a low concentration of polyaniline incorporated in them, as evidenced by the low intensity of the bands characteristic of this polymer.

On the other hand, in the PAN/PANI in situ fiber spectrum, the absorption bands associated with the presence of PANI-specific bonds were much more intense. A fuzzy peak above 3000 cm<sup>−</sup><sup>1</sup> was also visible, which was associated with the presence of water. This is not present in the PAN/PANI

blended spectrum. The bands occurring at 1414, 1194 and 879 cm<sup>−</sup><sup>1</sup> were characteristic of stretching in C–N between benzene and quinoid rings, and bending in C–H and 1,2,4 trisubstituted benzene rings. The absorption bands characteristic for polyacrylonitrile were also visible at 2940, 2244, 1726, 1629, 1445 and 1260 cm<sup>−</sup>1, which was characteristic of C–H stretching in polymer structures, stretching in C≡N, stretching in C=O, stretching in C=C, bending C–H in CH2, and stretching in C–N.

**Figure 5.** FTIR Spectra from the top: PANI powder (red); fibers: PAN/PANI blended (cyan); PAN/PANI in situ (green); and PAN (blue).

**Table 2.** Description of characteristic vibrations observed in the FTIR spectra of the tested substance.


1Where: υ—stretching, δ—bending, B—benzene ring, and Q—quinoid ring.

In addition, a band corresponding to the vibrations of the deprotonated polyaniline form (1160 cm<sup>−</sup>1) was present in both fibers containing polyaniline. Moreover, pure polyaniline was in a protonated form.

From the shifts in absorption bands in the PAN/PANI in situ fiber spectra, relative to unmodified polyacrylonitrile and polyaniline, it can be concluded that electrostatic interactions arose between the chains of these polymers between the polyaniline and nitrile groups. The confirmation of the interaction between polyaniline and the nitrile group of polyacrylonitrile was in the reduction of the intensity of the absorption band around 2244 cm<sup>−</sup><sup>1</sup> associated with stretching vibrations in C–N, and also the band around 3480 cm<sup>−</sup><sup>1</sup> associated with stretching N–H vibrations. In both cases, this reduction was more visible in the PAN/PANI in situ fibers. Such interactions between different conductive polymers and polyacrylonitrile are known in the literature [15]. These results confirmed

observations drawn from the research of the rheological properties of the obtained solutions and UV-Vis spectra.
