ATR-FTIR Spectroscopic Study on Hydrogen Bonding of Poly(N-isopropylacrylamide-co-sodium acrylate) Gel

Abstract

Diameter decrement by the repeated exchange of solvent water has been reported in a polyelectrolyte hydrogel ionized by sodium acrylate in its swollen state. This behavior has been attributed to the exchange of counterions of carboxyl groups and the formation of hydrogen bonding. In this paper, the formation and destruction of hydrogen bonding in poly(N-isopropylacrylamide-co-sodium acrylate) (NIPA/SA) gel were studied using Fourier transform infrared (FTIR) spectroscopy with attenuated total reflection (ATR) at 25 °C. Several swollen samples with different swelling ratios were prepared by changing the number of water exchanges at 25 °C. It was found that the ATR-FTIR spectra evidently depended on the initial swelling ratio. By sufficient water exchanges, new peaks appeared at ca. 1713 cm-1 (assigned to the carboxyl dimer) and at ca. 1650 cm-1 in the amide I region (assigned to a stretching vibration of the CO group that forms a hydrogen bonding with the N−H bond of a neighboring amide group), and the amide II band shifted to a smaller wavenumber by ca. 7 cm-1. From the detailed analysis of the IR spectra, the macroscopic polymer network shrinkage was attributed to the formation of three types of hydrogen bonding, that is, between two carboxyl groups of SA, between the carboxyl group of SA and the amide group of NIPA, and between two amide groups of NIPA. Moreover, the IR results indicated experimentally that the reswelling transition of the present system was caused by the destruction of hydrogen bonding on heating. It was concluded that not only the formation by the exchange of water but also the destruction of hydrogen bonding by heating is essentially important to determine the swelling ratio as well as the volume phase transition behavior in this system.

Adhesion properties of swollen hydrogels evaluated by a point‐contact method

“…Figure 6a shows the ATR FTIR spectra of the PSAAl(x) gel (x 5 1, 2, 3, and 4). As is shown in this figure, the overall features of the spectra were same and two strong absorption peaks were observed at around 1550 and 1410 cm 21 , which did not strongly depend on x. These peaks were assigned to the C¼ ¼O stretching vibration of the ionized carboxyl group (À ÀCOO 2 ).…”

“…These peaks were assigned to the C¼ ¼O stretching vibration of the ionized carboxyl group (À ÀCOO 2 ). On the other hand, the broad absorption peaks at 1750-1650 cm 21 and 1380-1150 cm 21 , which seemed to consist of multiple components, decreased monotonically with increasing x. This evidence indicated that the degree of crosslinking might affect the intermolecular force between the carboxyl groups and Al ions in a monotonic fashion with increasing x.…”

“…All spectra were found to involve CH 2 bending vibration consisting of two peaks at ca. 1463 cm 21 (1464 and 1446 cm 21 ). The total absorbance areas of the two peaks were assumed to be equivalent in the present experimental conditions, and the spectra were normalized by the total area.…”

Structural analysis of microbial poly(ɛ-L-lysine)/poly(acrylic acid) complex by FT-IR, DSC, and solid-state 13C and 15N NMR

“…11 As the e-PL content in the e-PL/PAA complexes increased, the C¼O stretching intensities of the dimer and the free forms decreased, and the intensity of the peak at 1402 cm À1 increased. Because the COO À stretching vibration was observed in the 1400 cm À1 region, 12 there was a third form of carboxyl groups that we refer to as the ionized form. IR measurements showed that three forms of carboxyl groups exist in the e-PL/PAA complex, namely (1) the ionized form, (2) the dimeric form and (3) the free form.…”

A novel reversible thermo-swelling hydrogel

“…Recently, Suzuki and coworkers reported that poly(sodium acrylate) (PSA) and poly(N-isopropylacrylamide-co-sodium acrylate) (NIPA-SA) gels deswelled under repeated exchange of external water, which was attributed to protonation of the carboxyl groups and the resultant formation of inter-and/or intramolecular HBs between -COOHs. Further interestingly, the gels showed a discontinuous reswelling at a certain elevated temperature because of the destruction of HBs [7,8]. However, the thermo-swelling was not reversible; namely, with decreasing the temperature the gel kept the swollen state.…”