Effect of Temperature on NMR Self-Diffusion in Aqueous Associative Polymer Solutions

Abstract

The temperature dependence of polymer self-diffusion rates in aqueous solutions of C12EO200C12 (AP9, Mw = 9300) and C12EO90C12 (AP4, Mw = 4600) and nonmodified analogues PEO10 and PEO4 (Mw = 10 000 and 3400) has been studied. The effect of the hydrophobic end-groups on the self-diffusion of the associative polymer (AP) was found to be proportional to the polymer content and inversely related to the temperature. The variation of the AP self-diffusion coefficient follows an Arrhenius behavior. The resulting apparent activation energies, Ea, increase with polymer content from 15 to 55 kJ/mol in the range 0.5−50 wt % for AP9, whereas the parent PEO10 shows an almost constant Ea of about 25 kJ/mol in the same concentration range. Activation energies derived from self-diffusion and low shear viscosity measurements were found to be quite similar. The distribution of self-diffusion coefficients often observed in AP systems is discussed in terms of distribution of aggregate sizes at low AP content and homogeneity ...