# Reactive Polymer Composite Microparticles Based on Glycidyl Metacrylate and Magnetic Nanoparticles
## 3 Results and Discussion
### Attempts of Chemical Modification and Application of Composite Microparticles
Impregnation products were found to contain 8.7 and 11.4 wt.% immobilized Pd(II) ions (0.81 and 1.07 mmol of Pd per gram), respectively. As is well known, palladium plays a crucial role in catalyzing different coupling reactions that deliver important products, for example, for the pharmaceutical [68, 69, 70, 71] and materials industries [69, 72, 73]. Numerous soluble and insoluble precursors were previously applied as a source of Pd(0) species that are responsible for activating substrates in these reactions. Among them, different modified polymeric, inorganic, and composite materials, including materials composed of magnetic nanoparticles, can be found [34, 74, 75, 76, 77, 78]. Therefore, the use of developed composite microparticles as a source of catalytically active palladium species appeared to be interesting. The Suzuki coupling observed between 4-bromoanisole and phenylboronic acid was chosen as a model reaction to carry out the catalytic experiments in the presence of selected materials (Scheme 4). Catalytic experiments were carried out at 70 \({}^{\circ}\)C using a 1.2-fold molar excess of phenylboronic acid PhB(OH)\({}_{2}\) and **3d** or **3e** in the amount corresponding to 0.5 mol% Pd. The mixture of \(i\)-PrOH/H\({}_{2}\)O (1:1; _v:v_) was applied as the reaction medium. Gas chromatography was used to determine the conversion of 4-bromoanisole after the assumed time periods. The catalysts used in the experiments were found to allow 4-bromoanisole to be quantitatively converted in approximately 60 min under the applied reaction conditions, al  
Figure 13: FTIR spectra of **2d** and **3d**. though the coupling reactions kicked off with some delay (Figure 14). The experiments also showed that **3e** with higher palladium (1.07 mmol/g) and magnetite loadings (0.068 wt.% Fe determined by ICP) turned out to be slightly more active than **3d** (0.81 mmol Pd(II)/g; 0.048 wt.% Fe from ICP analysis). Furthermore, it was concluded that the catalytic activities of **3d** and **3e** were considerably higher compared to the activity of the palladium catalyst based on gel-type polymer particles that were prepared without the addition of magnetite nanoparticles [65]. The presence of magnetite nanoparticles embedded within a gel-type polymer matrix can improve the dispersion of Pd(0) species on the surface and inside of a polymeric support, making them more active in the Suzuki reaction. The observed induction periods can result from the need for a preliminary transformation of inactive catalytically immobilized Pd(II) ions into active Pd(0) species, which occurs not only on the inert surface but also inside gel-type microbeads. Furthermore, the solvent used as the reaction medium does not favor the swelling of the polymer composite microparticles used as the palladium support, and more time is required for substrates to penetrate inside the polymer beads and interact with catalytic centers; however, the solvent that was used facilitates Suzuki coupling. Next, **3e** was used in the recycling experiments, and the results are presented in Figure 15. It was found that the catalyst induction time increased with each catalyst reuse. However, the activity remained at a high level even when **3e** was reused in the seventh cycle. The approximately 86% conversion of 4-bromoanisole in the reaction with boronic acids could then be obtained after 180 min. The decrease in the catalytic activity observed in the recycling experiments was probably due to the partial release of palladium nanoparticles from the support to the reaction mixture, as well as due to the deposition of larger, less active palladium black particles on the surfaces of the composite particles while the coupling occurs. The last factor was probably responsible for prolonging the induction times when **3e** was recovered and reused.