jp801127e_si_002.pdf (56.08 kB)
Phase Behavior of N-(Isopropyl)propionamide in Aqueous Solution and Changes in Hydration Observed by FTIR Spectroscopy
journal contribution
posted on 2008-04-17, 00:00 authored by Barbara Geukens, Filip Meersman, Erik NiesThe 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.