The functionality of associative polymer networks: the association behavior of hydrophobically modified urethane-ethoxylate (HEUR) associative polymers in aqueous solution

Abstract We re-examine the rheology of aqueous solutions of a hydrophobically modified urethane ethoxylate associative polymer with M n =51 000 containing C 16 H 33 end groups. Fluorescence data indicate that association commences at a very low concentration (about 10 ppm). Over a wide range of concentrations, the system forms spherical flower-like micelles consisting of about 10 looped chains. We determine the chain-end aggregation number to be 22 ± 2 end groups per micelle, independent of polymer concentration. Analysis of the rheology data indicates that larger structures are formed through secondary aggregation of the polymer micelles when the polymer concentration c pol > 0.2 wt.%. Treating the micelles as the fundamental building blocks of the secondary association, we calculate from the plateau modulus (at c pol > 1.2 wt.%) the effective functionality of the network and the fraction of chains that bridge neighboring micelles. Both of these parameters increase as the c pol increases.