Geukens Barbara, Meersman Filip, Nies Erik
Division of Molecular and Nanomaterials, Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
J Phys Chem B. 2008 Apr 17;112(15):4474-7. doi: 10.1021/jp801127e. Epub 2008 Mar 21.
The phase behavior of N-(isopropyl)propionamide (NiPPA), which is the repeat unit of poly(N-isopropyl-acrylamide) (PNiPA), in deuterated aqueous solution was investigated. Temperature induces a phase separation of NiPPA in aqueous solution above the lower critical solution temperature (LCST), as shown by optical microscopy. The phase behavior of NiPPA resembles that of PNiPA, but the demixing domain is much narrower. Monitoring the liquid-liquid phase separation by Fourier transform infrared (FTIR) spectroscopy reveals that a fraction of the NiPPA molecules becomes dehydrated above the LCST. Our findings therefore shed new light on the results of a recent dielectric relaxation experiment in which the behavior of NiPPA was found to be "completely contrary" to that of PNiPA. It is argued that the differences in the spectroscopic results of polymer and repeat unit solutions can be easily understood from the phase behavior of NiPPA and PNiPA.
对聚（N - 异丙基丙烯酰胺）（PNiPA）的重复单元N - （异丙基）丙酰胺（NiPPA）在氘代水溶液中的相行为进行了研究。如光学显微镜所示，温度会导致NiPPA在低于下临界溶液温度（LCST）时在水溶液中发生相分离。NiPPA的相行为与PNiPA相似，但相分离区域要窄得多。通过傅里叶变换红外（FTIR）光谱监测液 - 液相分离发现，高于LCST时，一部分NiPPA分子会脱水。因此，我们的研究结果为最近的介电弛豫实验结果提供了新的线索，在该实验中发现NiPPA的行为与PNiPA“完全相反”。有人认为，从NiPPA和PNiPA的相行为可以很容易地理解聚合物溶液和重复单元溶液光谱结果的差异。
