Numerous investigations have been carried out on such
Two models of HEUR (hydrophobically modified ethylene oxide APs in order to obtain information about the association urethane) associative polymers (AP) are compared. The two polymechanism, the aggregate size, shape, and internal structure mers are polyethyleneoxides simply end-capped with dodecyl . A loose aggregation, probably between EO chains, groups, one through an ether bond H 25 C 12 -O-(CH 2 CH 2 O) 304starts at very low concentration (6, 7, 22) long before forma-
C 12 H 25 (AP14, M w Å 13,700) and the other through an urethane tion of primary hydrophobic aggregates (micelles) (12, 16, bond H 25 C 12 -NHCOO-(CH 2 CH 2 O) 304 -CONH-C 12 H 25 (AP14-17, 19, 22) detected by fluorescence. As the concentration NCO, M w is about the same as for AP14). The results indicate of micelles increases, so does the number of AP molecules that this subtle difference in polymer architecture dramatically
bridging between them (13), so that micellar clusters coninfluences the initial association and the clouding of the polymer in water, so that AP14NCO starts to aggregate earlier but has a taining more than one hydrophobic domain form. Both the higher clouding temperature. However, at more elevated polymer average size of the clusters and the width of their size districontents (above 2-3 wt%) the differences in solution behavior and bution increase with increasing polymer concentration, as transport dynamics between the two polymers seems less signifiobserved by NMR self-diffusion measurements (10-12, 20, cant. These conclusions are drawn through fluorescence, dynamic 23). Above a critical concentration, a dramatic increase in light scattering, NMR self-diffusion, turbidimetry, and viscosity the viscosity (3, is generally observed for AP measurements.