“…In the infrared spectrum of SC-Gel (Figure 9C), the peak at 2873 cm À1 is assigned to the stretching vibration of methylene group, the peak at 1725 cm À1 is attributed to the stretching vibration of C O in carboxyl group, [54,55] and the stretching vibration peak of C O and N H in amide present respectively at 1652 and 1536 cm À1 , the peaks at 1350 and 1450 cm À1 correspond to the stretching vibration of C N in secondary amide and primary amide, respectively. [51][52][53] In the infrared spectrum of SP-Gel, the peaks at 1721 and 1658 cm À1 correspond to the stretching vibration of C O in ester group and amide group, respectively, while the peaks at 1540 and 1450 cm À1 correspond to the absorption of N H and C N in amide, respectively, [56][57][58] the characteristic peaks of sulfonic acid group located at 1238 and 1088 cm À1 . [59,60] By comparing the spectra of IPN IPN-Gel and two single networks SC-Gel and SP-Gel, we can see that the main infrared absorption peaks of single network SC-Gel and SP-Gel appear on the infrared spectrum of IPN-Gel, and the characteristic peaks of carbonyl groups in ester group and amide group are located at 1724 and 1662 cm À1 , respectively, and the characteristic peaks of sulfonyl group shift to 1248 and 1064 cm À1 , indicating that IPN-Gel is not a simple physical mixing of two signal networks.…”