Phase Separation in Water-Ethanol Polymer Solutions Studied by NMR Methods

We applied H and C NMR spectroscopy to investigate a phase transition and a cononsolvency effect of uncharged poly(N-isopropylmethacrylamide) (PIPMAm) and negatively charged PIPMAm copolymers in water/ethanol (D2O/EtOH) mixtures. For this purpose several PIPMAm solutions with various volume mixture compositions of D2O/EtOH (100/0 5/95 vol.-%) were prepared; sodium methacrylate was used as an ionic comonomer. Neat binary D2O/EtOH mixtures with the same compositions were studied for the comparison to be able to distinguish between effects caused by the phase transition and effects caused by the properties of binary D2O/EtOH mixtures. It is obvious from H and C spectra that with increasing temperature the concentration range of the phase separation broadens to lower values of ethanol content in the solution. We observed a difference in characteristics of the phase transition induced by a change of temperature or by a change of solvent composition. When the phase separation is induced by the solvent composition polymer groups at the ends of dangling chains are more mobile than those in backbone chains. After the temperature-induced phase transition PIPMAm groups behave in the same way. We confirmed this when investigating solvent dynamic properties by means of ethanol C T2. We found out that charge in chains prevents the polymer solution from the phase separation by strenghtening interactions between polymer and solvent.