## 2 Results and Discussion
### Mechanism of Aerobic Oxidation of PMT over Copolymer Catalysts  
As noted in Scheme 2, three major products were formed by the aerobic oxidation of PMT over the developed copolymer catalysts. The profiles of their yields are shown in the same way as the PMT conversion in the 2D maps in Figure 5. Six zones of yield values are indicated in the maps with different colors-- \(<\) 1% (blue, zone I), 1-3% (dark green, zone II), 3-5% (light green, zone III), 5-7% (yellow, zone IV), 7-9% (orange, zone V), and \(>\) 9% (red, zone VI). In addition, the exact values of yields and selectivities of the individual products after 6 h of the reaction are summarized in Tables S1-S3 in the Supplementary Materials. Figure 5: Yields of p–anisyl alcohol, p–anisaldehyde, and p–anisic acid 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\({}_{2}\)). After 1 h the yields of all products are relatively low and do not exceed 5% (for p-ansyl alcohol < 3%, p-ansaldehyde < 5 %, and p-anisaldehyde < 3%). During the second hour, the yields of alcohol and aldehyde increase markedly. The best catalysts reach zone III for the alcohol production, and even zone V for the aldehyde formation. The acid is still below zone III. During the third hour, the amounts of all products are significantly higher. The alcohol yields are <7% and maintain this level until the catalytic test is complete. For comparison, in the case of aldehyde, a further increase in its amount is observed from 3 to 5 h of the reaction, in which the p-anisaldehyde yields enter zone VI for the most active catalysts. Interestingly, after 5 h, a slight decrease in the p-anisaldehyde yields (to values below 9%) is found. Furthermore, prolonged reaction time has a very positive effect on the p-anisic acid formation. After the third hour, the best catalysts show the acid yields in zone III, after the fourth and fifth hour in zone V, and after the six hours in zone VI. It should be emphasized that the yields above 9% at the end of the reaction are only noted for p-anisic acid--both p-ansil alcohol and p-anisaldehyde remain in smaller quantities. Such changes in the products profile clearly suggest the occurrence of subsequent reactions in which initially produced p-anisyl alcohol is converted into p-anisaldehyde, and this, in turn, into p-anisic acid. These observations lead directly to the formulation of possible reaction mechanism (Scheme 4) that links the activity of NHPI and Co(OAc)\({}_{2}\) as complementary components of the catalytic system for the aerobic oxidation of PMT. The lack of any of these components causes the system to stop working effectively. We tested the reaction in the presence of the best copolymer catalyst without the addition of Co(II) salt, as well as using only Co(II) acetate without the participation of NHPI, and in both cases after 6 h of the reaction, the PMT conversion ranged from 1.0% to 1.2%. A key step in the free-radical reaction of aerobic oxidation of PMT is the generation of phthalimide \(N\)-oxyl radicals (PINO) from the NHPI species. PINO are initially formed with the involvement of azobisisobutyronitrile (AIBN), which at an elevated temperature decomposes into two 2-cyanoprop-2-yl radicals and a N\({}_{2}\) molecule evolved to the gas phase. The presence of PINO enables the entire cycle of transformations based on the activation of the C-H bond through hydrogen atom transfer [54; 55]. Namely, the CH\({}_{2}\) radicals are generated in the methyl group of PMT, which subsequently react with molecular oxygen giving corresponding peroxy radicals. Finally, the hydroperoxide compound is produced by abstraction of hydrogen from another NHPI functionality. Despite the unlikely termination of PINO [5], the described transformation chain may be interrupted and the reconstruction of PINO would become impossible.