## 3 Results and Discussion
### Thermal Analysis in Air
The third step up to 446.2 \({}^{\circ}\)C (maximum decomposition rate as much as 16.8%/min at 416.2 \({}^{\circ}\)C) with a mass loss of 58.4% is the most intense transformation in this experiment, and this is a decarboxylation process of the previously dehydrated structure (polyanhydride decomposition through decarboxylation and elimination of CO\({}_{2}\) and CO) [61; 62; 63; 64; 65]. The last decomposition step up to 503.8 \({}^{\circ}\)C corresponded to the oxidative degradation (combustion) of polymeric matrix when oxygen (\(\sim\)20.8% volume) interacts with the hydrocarbon chain and its degradation products. The residue left at 900 \({}^{\circ}\)C is ash and is about 0.9% of the original sample. The described transformations due to the accompanying changes and mass losses corresponded well to the results described in the work [62], where by mass spectrometry, volatile process products were identified, and FTIR analysis confirmed the formation of polymeric anhydrides as intermediate products of CCE thermal decomposition. The TG/DTG curves of M/Cu, M/Cu#CuO, and M/H#CuO in air (Figure 3b-d) have a similar course but are significantly different in comparison to the parent resin (Figure 3a). When analyzing the data from these three experiments, it should be taken into account that although organic matter in them dominates, it represents no more than 75% of their mass (and in one case only 60%). For this reason, the mass loss for the particular stages is smaller than in the case of the parent resin. Analyzing the first transformation corresponding to the evaporation of water molecules, one can see that the samples in which the functional groups in the Cu\({}^{2+}\) form are much more hydrated (a greater mass loss is observed on the TG curve) than the samples containing the functional groups in the H\({}^{+}\) form. In each experiment, the presence of copper in the tested material, as Cu\({}^{2+}\) ions in functional groups and as CuO particles in the resin matrix, significantly accelerated the thermal decomposition of the host material. The decomposition of these samples ended at a temperature 100 \({}^{\circ}\)C lower than that of M/H alone. The significant acceleration of thermal decomposition can be observed in a temperature range of 200-300 \({}^{\circ}\)C, where there are two broad peaks indicating intense decomposition of functional groups, and especially very fast decarboxylation (at a temperature of about 150 \({}^{\circ}\)C lower than pure resin). All residues left at about 900 \({}^{\circ}\)C had a mass slightly higher than the copper content in the output sample. In the case of the sample containing the most copper (M/Cu#CuO, 32.7 wt% Cu), the residue represented about 39.2 wt% of the original sample. Figure 4 shows the results of similar studies in air, in which as support for copper(II), the gel-like cation exchanger was used. According to Figure 4a, dehydration of G/H (maximum decomposition rate at 175.5 \({}^{\circ}\)C with a mass loss of 6.0%) was proceeding at a higher temperature than dehydration of M/H (maximum decomposition rate at 78.4 \({}^{\circ}\)C, Figure 3a). Again, it turned out that the resin in the H\({}^{+}\) form contained little water, and the compact structure of the gel matrix without real pores (strongly shrinking during drying) made it difficult for water molecules to escape outside [39]. A significant difference in the thermal decomposition of G/H compared to M/H was observed at 200-300 \({}^{\circ}\)C. A mass loss of as much as 21.0% (maximum decomposition rate at 285.0 \({}^{\circ}\)C) indicated that for G/H, the changes taking place went beyond water elimination between two neighboring carboxylic groups with the creation of some polyacrylic cyclic anhydrides by intramolecular dehydration, as in the case of M/H. The intermolecular dehydration probability with the  
isobutyric anhydride formation (Scheme 2) resulted from the compact structure of the dry gel matrix and the proximity of polymer chains [62; 64; 65].