# A View on the Synthesis and Characterization of Porous Microspheres Containing Pyrrolidone Units
## 3 Results and Discussion  
Crosslinked porous polymers can be synthesized via a range of polymerization techniques. In this study, a suspension polymerization technique was chosen because it enabled the synthesis of porous microspheres with diameters of approximately 100 \(\upmu\)m (Figure 1). Such a diameter is required in many essential techniques like PALS studies, gas chromatography, catalysis, etc. However, a serious drawback of this technique is the quite broad size distribution of the synthesized microspheres [41]. Figure 2 presents two graphs that compare the relative distributions of microsphere volume as a function of diameter for the poly(GMA-_co_-EGDMA)_1 and poly(NVP-_co_-EGDMA)_1 copolymers. The graphs depict the particle size distributions, showing how the volume percentage is distributed over different particle sizes. The overall shape of both distributions exhibited a log-normal pattern, as expected in suspension polymerization. The tailing effect was minimal. The maximum of the peak, which represented the most frequent particle size in the distribution of poly(GMA-_co_-EGDMA)_1, was visible at about 100 \(\upmu\)m. For the poly(NVP-_co_-EGDMA)_1 copolymer, the peak was slightly shifted and occurred at about 80 \(\upmu\)m. It was well defined with less tailing. What's more, the particle size distribution was narrower, meaning that most particles fell within a relatively confined size range. Generally, better uniformity in microsphere size is more desirable in most applications. As is shown, the application of the NVP functional monomer in polymer synthesis provided better size control compared with the use of GMA. Figure 1: SEM photographs of the investigated microspheres: (**a**) poly(GMA-_co_-EGDMA)_1 copolymer; (**b**) poly(NVP-_co_-EGDMA)_1 copolymer. The main objective of the presented study was to synthesize porous microspheres containing pyrrolidone units. In the first part of the study, copolymerization of N-vinyl-2-pyrrolidone with ethylene glycol dimethacrylate was performed. The molar ratio of NVP to EGDMA used in the synthesis was progressively adjusted from an initial 1:1 up to 4:1. The proper course of polymerization was monitored with the use of FTIR-ATR spectroscopy (Figure 3). In the first panel (a) of Figure 3, the ATR spectrum of poly(VP-\(\omega\)-EGDMA)_1 is presented. As can be seen, the bands characteristic of alkyl and alkylene groups, i.e., at 2962-2951 cm\({}^{-1}\) (v C-H) and 1459-1425 cm\({}^{-1}\) (s C-H), are present. The occurrence of the ester group is revealed by the band at 1726 cm\({}^{-1}\) (v C=O) and confirmed by the bands at 1196-1087 cm\({}^{-1}\) (v C-O). The band at 1673 cm\({}^{-1}\) is related to the \(\gamma\)-lactam ring present in NVP (the C=O stretching vibrations). Additionally, the presence of pyrrolidone units was confirmed by elemental analysis. The synthesized copolymers contained from 2.8 to 6.4% nitrogen depending on the molar ratio and diluent type (Table 2). As expected, the increment in NVP quantity in the polymerization mixture led to an elevated nitrogen proportion in the synthesized copolymer. The determined nitrogen percentage for poly(NVP-\(\omega\)-EGDMA)_1 copolymer was 3.01, whereas for poly(NVP-\(\omega\)-EGDMA)_8, in which the molar ratio of NVP to EGDMA equaled 4:1, it increased to 6.40. The presented values were lower than theoretically calculated values and indicated that only about 70% of the NVP initial amount was incorporated into the polymeric matric. However, this value was much higher in comparison to the poly(NVP-\(\omega\)-DVB) copolymer investigated in an earlier study [40]. The results for the copolymers derived from equimolar ratios of monomers revealed the impact of diluent composition. The lowest nitrogen amount was  
Figure 3: ATR spectra of the investigated copolymers: (**a**) poly(VP-\(\omega\)-EGDMA)_1 (green line); (**b**) parent poly(GMA-\(\omega\)-EGDMA)_1 (red line), modified poly(GMA-\(\omega\)-EGDMA)_1+p (blue line).