# A View on the Synthesis and Characterization of Porous Microspheres Containing Pyrrolidone Units
## 3 Results and Discussion
In systems with elevated crosslinker content, the onset of phase separation was accelerated. However, the higher crosslinker density of the nuclei limited their ability to adsorb additional monomer. In addition, increased crosslinker density suppressed the tendency of particles to coalesce. As a result, the large number of small nuclei remained large, and it was responsible for the highly developed internal structure. A reduction in the crosslinker content within the polymerization medium led to a decrease in the specific surface area. The copolymers synthesized with a higher amount of functional monomer were characterized by a larger content of nitrogen in their structure but a considerably lower porous structure. This parameter decreased from 456 m\({}^{2}\)/g for poly(NVP-_co_-EGDMA)_1 to 56 m\({}^{2}\)/g for poly(NVP-_co_-EGDMA)_8. Relatively polar monomers bearing both hydrophilic and hydrophobic units (e.g., NVP) increased the agglomeration tendency of crosslinked nuclei. The nuclei grew together. The loss of structural distinction among the particles corresponded with lower porosity. A similar situation was observed in the case of the application of more polar diluent (decan-1-ol). Compared with apolar dodecane, it promoted the incorporation of NVP into the polymeric matrix but led to a diminution of the specific surface area to about 80 m\({}^{2}\)/g. Another approach to obtain polymers with a developed internal structure and bearing pyrrolone units is the production of poly(GMA-_co_-EGDMA) copolymers and their modification with pyrrolone. The processes of polymerization and subsequent modification were monitored using infrared spectroscopy. In the second panel (b) of Figure 3, the spectra of the parent poly(GMA-_co_-EGDMA)_1 (red line) and modified pyrrolone poly(GMA-_co_-EGDMA)_1+p (blue line) copolymers are displayed. In the ATR spectrum of the functionalized copolymer, significant reductions in the peak absorbances at 906 and 844 cm\({}^{-1}\), related to the epoxy ring, are visible. Meanwhile, a new peak at 1663 cm\({}^{-1}\) emerges, attributed to pyrrolone subunits, indicating the successful transformation of epoxy groups into pyrrolone. Furthermore, a broad peak within the range of 3290-3300 cm\({}^{-1}\) related to O-H stretching vibrations can be seen. Additionally, the modification step influenced the porosity of the resulting copolymers. The porous structure of the modified copolymers slightly decreased. This observation was in accordance with previous ones. As some of the potential applications of porous microspheres require good thermal stability, it was of interest to investigate their thermal behavior. It was evaluated on the grounds of TG and DSC methods. Figure 5 displays the TG curves of the investigated copolymers, whereas their first derivatives are presented in Figure 6.  
On the basis of their characteristic temperatures, the T\({}_{5\%}\), T\({}_{20\%}\), and T\({}_{50\%}\) mass losses as well as the maxima of mass loss were determined and are collected in Table 3. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Copolymer** & **T\({}_{5\%}\)** & **T\({}_{20\%}\)** & **T\({}_{50\%}\)** & **T\({}_{1\text{max}}\)** & **T\({}_{2\text{max}}\)** \\  & (\({}^{\circ}\)**C**) & (\({}^{\circ}\)**C**) & (\({}^{\circ}\)**C**) & (\({}^{\circ}\)**C**) & (\({}^{\circ}\)**C**) \\ \hline poly(NVP-_co_-EGDMA)\_1 & 317 & 355 & 394 & 417 & - \\ poly(GMA-_co_-EGDMA)\_1 & 251 & 265 & 288 & 272 & 369 \\ poly(GMA-_co_-EGDMA)\_2 & 245 & 257 & 276 & 265 & 367 \\ poly(GMA-_co_-EGDMA)\_1+p & 283 & 337 & 385 & 350 & 404 \\ poly(GMA-_co_-EGDMA)\_2+p & 277 & 301 & 348 & 334 & 370 \\ \hline \end{tabular}
\end{table} 
Table 3: TG and DTG data of the copolymers determined in a helium atmosphere. Figure 5: TG curves of the investigated copolymers: (**a**) poly(NVP-_co_-EGDMA)\_1 (red line); (**b**) parent poly(GMA-_co_-EGDMA)\_1 (green line) and modified poly(GMA-_co_-EGDMA)\_1+p (blue line).