## 2 Results and Discussion  
### Effect of Composition of Copolymer Catalysts on Activity in Aerobic Oxidation of PMT  
The aerobic oxidation of PMT is often used as the model reaction for testing various compounds and materials for their catalytic activity in the selective oxidation of organic substrates [20; 46; 47]. As shown in Scheme 2, the reaction proceeds with the formation of three major products, i.e., 4-methoxybenzyl alcohol (p-anisyl alcohol), 4-methoxybenzaldehyde (p-anisaldehyde), and 4-methoxybenzoic acid (p-anisic acid). In the catalytic tests, we used conditions that allow relatively easy comparison of the results obtained in the presence of NHPI-containing catalysts with the literature data, e.g., [20; 47; 48]. Furthermore, the temperature of 80 \({}^{\circ}\)C was selected to achieve the optimal reaction rate. It should be kept in mind that at higher temperatures decomposition of NHPI catalysts through self-decay of PINO radicals is favored [49; 50]. We used fixed amounts of Co(II) acetate as a co-catalyst and AIBN as a radical initiator as well. It is worth emphasizing that no additional solvent was added. Changes in the PMT conversion observed under such reaction conditions during six-hour catalytic runs carried out in the presence of the developed NHPI-containing copolymer catalysts are presented in the form of two-dimensional maps in Figure 1. The maps collected at 1 h steps show the effect of the amount of the monomer with NHPI groups and the cross-linking degree (the DVB content) on the catalytic activity, while for the sake of simplicity six zones of the PMT conversions are distinguished with different colors--\(\sim\) 5% (blue, zone I), 5-9% (dark green, zone II), 9-13% (light green, zone III), 13-17% (yellow, zone IV), 17-21% (orange, zone V), and > 21% (red, zone VI). Figure 1: Conversion of PMT in the presence of the copolymer catalysts with different NHPI loadings and cross–linking degrees measured during 6 h tests at 80 \({}^{\circ}\)C (0.1 g copolymer catalyst, 5.0 mg AIBN, 5.0 mg Co(OAc)\({}_{2}\)-4H\({}_{2}\)O, 2.0 mL PMT, 1 atm O\({}_{2}\)). The presence of NHPI functionalities makes all the synthesized copolymer catalysts active in the aerobic PMT oxidation. The achieved conversion of substrate, however, strongly depends on the reaction time, as well as the composition of the catalyst, which determines the content of active functional groups (provided by the NHPI monomer) and the cross-linking degree (depended on the amount of DVB monomer). After 1 h, three catalysts, i.e., 30%NHPI_5%DVB, 40%NHPI_3%DVB, and 60%NHPI_5%DVB, reach the activity at zone II. Two of them (30%NHPI_5%DVB and 60%NHPI_5%DVB) come to zone IV after 2 h, and to zone V after 3 h of the test. Achieving zone VI, where the PMT conversion exceeds 21%, is much more difficult. Among the tested materials, only 60%NHPI_5%DVB (after 4 h), 30%NHPI_7%DVB (5 h), 30%NHPI_9%DVB (6 h), 40%NHPI_7%DVB (6 h) and 50%NHPI_7%DVB (6 h) show so high activity. It can be noticed that some catalysts, despite the high initial reaction rate, are not able to bring the reaction system to a sufficiently high degree of PMT conversion. On the other hand, a very interesting picture of the possibility of using the developed catalysts is drawn on the basis of the analysis of the results collected after 6 h (Table 1). At the end of the reaction, the most efficient catalysts form a specific diagonal in the matrix extending between 30%NHPI_9%DVB and 60%NHPI_5%DVB. This feature evidently indicates the mutual influence of at least two parameters (including active sites concentration and cross-linking degree) on the catalytic activity. If we compare the catalytic behavior of the materials on the left side of the diagonal with those on the right side, we notice a clear difference in the final PMT conversions. The catalysts with lower NHPI loadings and cross-linking degrees show much better catalytic performance than the materials with higher numbers of NHPI groups, which are additionally more strongly cross-linked.