Temperature-induced fractionation of a quasi-binary self-associating polymer solution. A phase behavior and polymer self-diffusion investigation

Dynamic properties of quasi-binary aqueous solutions of ethyl(hydroxyethyl) cellulose (EHEC) and the hydrophobically modified analogue (HM-EHEC) have b een investigated with the PFG-SE NMR technique. By taking advantage of the phase behavior of the (HM-)EHEC solutions, different polymer fractions coul d be obtained by simply adjusting the temperature within the two-phase regi on and collecting the coexisting phases. We discuss the connection between phase behavior, microphase structure, polymer structure, and polymer dynami cs by following the self-diffusion of polymers in these fractions as a func tion of concentration and temperature. By extrapolating the diffusion coeff icient to infinite dilution, we observe a significant difference in hydrody namic radius between the separated fractions. The width of the distribution of diffusion coefficients is used to recognize differences in associative behavior of the different polymer fractions. The echo decays of highly asso ciative fractions show, in addition to the characteristic curved echo decay commonly observed in solutions of associative polymers, a single diffusing component with a very slow diffusion coefficient (D similar to 10(-14) m(2 ) s(-1)).