A FTIR and 2D-IR Spectroscopic Study on the Microdynamics Phase Separation Mechanism of the Poly(N-isopropylacrylamide) Aqueous Solution
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- 作者：Bingjie Sun ; Yinan Lin ; Peiyi Wu ; Heinz W. Siesler
- 刊名：Macromolecules
- 出版年：2008
- 出版时间：February 26, 2008
- 年：2008
- 卷：41
- 期：4
- 页码：1512 - 1520
- 全文大小：363K
- 年卷期：v.41,no.4(February 26, 2008)
- ISSN：1520-5835
文摘
The thermal behavior of PNIPAM in its concentrated D2O solution (20 wt %) was studied byFTIR and 2D-IR correlation spectroscopy. The spectral data of the C-H groups and the Amide I region providedetails about the changes of the hydrophobic and hydrophilic parts in the polymer respectively during a heating-cooling cycle. The reversal of peak positions of the C-H bands upon cooling indicates the reversibility oftemperature-induced dehydration of the hydrophobic groups. The change in hydrogen bonding of C=O···D-Nconstructed between dehydrated C=O and N-D groups, as derived from the Amide I region, does not revertprecisely in the cooling process due to the newly formed hydrogen bonds in the collapsed state, and a hysteresisphenomenon is observed. In our concentrated solution (20 wt %), the strength of those intra- and interchainhydrogen bonds even prevent the polymers from dissociating completely below the LCST during the coolingprocess. The microdynamics phase separation mechanism was obtained by application of the 2D-IR analysis tothe spectral data. When the temperature rises, the two-step dehydration of the CH3 groups occurs first, then themain-chain diffusion and aggregation takes place, and finally the hydrogen bond transition occurs. The dynamicsequence in the cooling process is also described.