## 3 Results and Discussion
### Investigation of PVC Photodegradation Using FTIR Spectroscopy  
The PVC photooxidation caused cross-linking, bond breaking, and chain scission mainly caused by the HCl (dehydrochlorination) elimination. Subsequently, this process caused the loss of small fragments containing different functional groups, such as hydroxy (OH; alcohols and hydroperoxides), carbonyl (C=O; ketones and chlorketones), and alkene (C=C; polyenes) [53]. The changes in the absorption band vibrations of the OH (3510 cm\({}^{-1}\)), C=O (1717 cm\({}^{-1}\)), and C=C (1610 cm\({}^{-1}\)) groups in the FTIR spectra could be used to assess the photod stabilization effect induced by the additives [54]. The changes in the intensity of the peaks corresponding to these functional groups were compared herein with those of the CH\({}_{2}\) bonds (1328 cm\({}^{-1}\)), which were not affected during irradiation [55]. Complexes **1-4** at 0.5% concentration were added to PVC, and thin films were produced. Such a concentration showed the most desirable stabilizing effect for PVC without causing changes in color [56]. The films were irradiated with UV light. The FTIR spectra were recorded every 50 h and up to 300 h. The functional group index (\(l_{s}\)) for OH, C=O, and C=C was calculated from its absorbance (\(A_{s}\)) and for the reference group (\(A_{r}\); CH\({}_{2}\)) using Equation (1). The FTIR spectra of the pure PVC film before and after irradiation (300 h) is shown in Figure 1.  
\[I_{s}\ =\ A_{s}/A_{r} \tag{1}\]  
Figures 2-4 depict the IOH, JC=O, and JC=C for the pure and blended PVC films with complexes at various irradiation times (50-300 h), respectively. The changes in the IOH were very significant after the beginning of irradiation (50 h) and sharper for the pure PVC film (Figure 2). At the end of irradiation (300 h), the IOH was 0.95 for the pure PVC  
Figure 1: FTIR spectra of PVC film: (**a**) before and (**b**) after irradiation.  
compared with 0.51 for the film containing complex **1**. The PVC photodegradation that led to small polymeric fragments containing a hydroxyl group for pure film was approximately two-fold (187%) compared with that for the PVC + **1** blend. The complex containing the high aromatic content (three phenyl groups; complex **1**) was the best PVC photod stabilizer, followed by that containing two phenyl groups (complex **2**) and those containing alkyl (butyl and methyl) substituents (complexes **3** and **4**). Complex **1** behaved as a good UV absorber and a scavenger for radicals and HCl as a result of its high aromaticity.  
Figure 3: The JC=O of the PVC films versus time.  
Figure 2: The JOH of the PVC films versus time.  
Figure 3 shows that increasing the irradiation time led to a significant increase in the IC=O; however, the changes were sharp up to 50 h. The IC=O was 1.15 for pure PVC, 0.60 for PVC + **1**, 0.69 for PVC + **2**, 0.74 for PVC + **3**, and 0.82 for PVC + **4** at the end of irradiation. Complexes **1-4**, particularly those with highly aromatic qualities, provided significant protection to PVC against photodegradation.  
Similar to both the JOH and IC=O, the changes in the IC=C were larger for the pure PVC film (0.81 after 50 h and 1.15 after 300 h) than those with the polymeric blend containing **1** (0.45 and 0.58 after 50 and 300 h, respectively). Additive **1**, again, showed the highest stabilizing effect, followed by **2**, **3**, and **4**. Complexes **1-4** showed similar or better stabilizing performance compared with those reported for other additives [14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35].