## 3 Results and Discussion
### Characterization of PAAm, PAMPS, and PAMPS-Na Microgels  
The chemical structures of PAAm, PAMPS, and PAMPS-Na are investigated from FTIR spectra represented in Figure 1a-c. The disappearance of vinyl =CH stretching, C=C stretching, and =CH out of plan bending absorption bands at 3100-3000 cm\({}^{-1}\), 1550 cm\({}^{-1}\), and 900-1000 cm\({}^{-1}\), respectively elucidates the crosslinking polymerization of PAAm, PAMPS, and PAMPS-Na. The appearance of new strong band at 3462 cm\({}^{-1}\), NH stretching, elucidates the incorporation of MBA with PAAm, PAMPS, and PAMPS-Na. The shift of wavenumber values of the strong intense CONH at band 1666 cm\({}^{-1}\) (Figure 1a), 1697 cm\({}^{-1}\) for PAMPS and PAMPS-Na observed (Figure 1b,c), or the S=O asymmetric stretching and symmetric S=O stretching at 1400 and 1043 cm\({}^{-1}\) (Figure 1b,c) compared to their reported values in the literature [35] elucidate the decreasing of PAAm, PAMPS, and PAMPS-Nasizes [36]. These shifts refer to the decrease in the wavelength and penetration depth of the IR light intensity [37]. The thermal stabilities of PAAm, PAMPS and PAMPS-Na were investigated from their TGA thermograms represented in Figure 2 a-c. The thermograms indicate that all microgels lost from 2-4 Wt. % from their original weights at 100 \({}^{\circ}\)C to confirm the hydrophilicity of microgels to bind with the air moisture or bound water [38]. The PAAm, PAMPS, and PAMPS-Na lost 10 Wt. % from their original weights at 210, 240 and 310 \({}^{\circ}\)C, respectively. These data confirm that the PAMPS-Na has the greatest thermal stability due to the absence of sulfonic acid groups that highly degraded at lower temperature. By comparing these values with that reported in the literatures [38], it can be elucidated that the thermal stabilities of the PAAm, PAMPS, and PAMPS-Na microgels are greater than their corresponding hydrogels. The remained residues at 600 \({}^{\circ}\)C is for PAMPS-Na, PAMPS and PAAm microgels were 33.3, 17.8 and 20 Wt. %, respectively. Moreover, it was also observed that at temperature range from 250 to 550 \({}^{\circ}\)C, the PAMPS-Na, PAAm and PAMPS lost 60, 65 and 70 Wt. % from their original weights, respectively. The prepared microgels show higher thermal stability than their corresponding hydrogels which contradict with the statement of decreasing thermal stability of polymers with decreasing particle sizes [39]. Consequently, the thermal stability of the prepared microgels can be arranged in the order PAMPS-Na > PAAm > PAMPS microgels. The morphologies of the prepared PAAm, PAMPS, PAMPS-Na microgels were investigated from their TEM micrographs represented in Figure 3a-c. All microgels show spherical morphology, which is more uniform in PAMPS-Na microgel (Figure 3c). The uniform spherical morphology of PAMPS-Na can be attributed to the repulsion between negative charges of the ionic sulfonate groups that increases with complete ionization and formation of sodium sulfonate. The non-uniform spherical morphology with the agglomeration is observed for PAAm and PAMPS (Figure 3a,b), which refereed to the interactions between the PAAm and PAMPS with the nonionic surfactants Span 80 and Tween 60 [38; 39; 40]. Figure 1: FTIR spectra of (**a**) PAAm, (**b**) PAMPS, and (**c**) PAMPS-Na. The hydrodynamic diameter and polydispersity index (PDI) of the prepared PAAm, PAMPS, and PAMPS-Na in deionized water are represented in Figure 4a-c. The relations of hydrodynamic diameter and surface charges of the prepared PAAm, PAMPS, and PAMPS-Na microgels versus pH of solutions are determined and represented in Figure 5a-c. The formation of agglomerates is observed in PAAm and PAMPS graphs (Figure 4a,b). There is agreement between this observation and the data obtained from the TEM micrographs (Figure 3a-c). The hydrodynamic diameter of the prepared microgels observed by DLS measurement (Figure 4a-c) is greater than that obtained from TEM data (Figure 3a-c). This increase is attributed to swelling of microgel particles in the water more than when dry.