EFFECT OF TEMPERATURE ON NMR SELF-DIFFUSION IN AQUEOUS ASSOCIATIVE POLYMER-SOLUTIONS

The temperature dependence of polymer self-diffusion rates in aqueous solutions of C(12)EO(200)C(12) (AP9, M(w) = 9300) and C(12)EO(90)C(12) (AP4, M(w) = 4600) and nonmodified analogues PEO10 and PEO4 (M(w) = 1 0 000 and 3400) has been studied. The effect of the hydrophobic end-gr oups on the self-diffusion of the associative polymer (AP) was found t o be proportional to the polymer content and inversely related to the temperature. The variation of the AP self-diffusion coefficient follow s an Arrhenius behavior. The resulting apparent activation energies, E (a), 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 E(a) of about 25 kT/mol in the same concentration range. Activation en ergies derived from self-diffusion and low shear viscosity measurement s were found to be quite similar. The distribution of self-diffusion c oefficients often observed in AP systems is discussed in terms of dist ribution of aggregate sizes at low AP content and homogeneity of the n etwork at higher contents. The residence time of an AP monomer in a hy drophobic domain was estimated as 0.1 ms at 25 degrees C and decreases with temperature. Also included are turbidity measurements on the AP systems.