*3.2. Infrared Spectroscopy and Themal Analysis*

The PVC-*g*-4VP/4VPPS materials were characterized by infrared spectroscopy to determine the presence of the different functional groups, as shown in Figure 3. The control PVC catheter spectrum presented bands at 2992 cm−<sup>1</sup> of C-H stretching of -CH2- groups, 1267 cm−<sup>1</sup> of C-H flexions; additionally, bands at 1745 and 1459 cm−<sup>1</sup> were presented, which are characteristics of the plasticizer. The PVC-*g*-4VP spectrum, apart from the previous bands, presented C=C stretching signals at 1597 and 1557 cm<sup>−</sup>1, and at 830 cm−<sup>1</sup> of the C-H bends outside the plane of the aromatic amine [34,35]. Finally, the PVC-*g*-4VP/4VPPS spectra, together with the characteristic bands of the aromatic amine, show bands at 1039 and 1265 cm−<sup>1</sup> corresponding to the symmetric and asymmetric stretching of the sulfonate group (SO3 <sup>−</sup>), and the band 1680 cm−<sup>1</sup> of the C=N stretches of the pyridine, corroborating the formation of the zwitterion 4VPPS [36].

**Figure 3.** Infrared spectra of the neat and grafted PVC catheters using ATR module.

TGA thermal analysis showed that the catheter PVC-*g*-4VP/4VPPS has greater thermal stability than PVC and PVC-*g*-4VP because it lost 10% weight at a temperature 18 ◦C higher (Table 2). PVC and PVC-*g*-4VP presented three decomposition temperatures: the first was attributed to the decomposition of the plasticizer, the second and more intense was produced by the dehydrochlorination of PVC, and the last was attributed to the total chain decomposition; the materials modified with 4VP presented an increase of around 20 degrees at all decomposition temperatures. Finally, the PVC-*g*-4VP/4VPPS catheters showed four decomposition temperatures: the first was at 272 ◦C due to the loss of the plasticizer, the second was at 333 ◦C due to the dehydrochlorination of PVC [37], the third was at 364 ◦C, which is consistent with the decomposition of the quaternary amine [38], and the last was at 453 ◦C, which corresponds to the carbon chain decomposition. Figure 4 shows the thermograms of each sample.

**Table 2.** Thermogravimetric analysis.


**Figure 4.** Thermograms: (**a**) PVC, (**b**) PVC-g-4VP, and (**c**) PVC-g-4VP/4VPPS.
