Lifetime and network relaxation time of a HEUR-C20 associative polymer system

The end-capped telechelic HEUR associative polymer was reported to exhibit a single mode Maxwell typed relaxation behavior. Annable et al. (1993) sugg ested that the single mode Maxwell relaxation time corresponded to the life time of the hydrophobe in the micellar junction. However, results from some recent publications suggested that a more complex relaxation behavior exis ted. In order to verify this, a hydrophobically modified urethane-ethoxylat e (HEUR) polymer with M-n of 26 000 and a C20H41 hydrophobe was synthesized for the present study. Results from oscillatory measurements of a 2 wt % s ample in distilled water indicates that two different relaxation modes are present. This is confirmed with a two-mode Maxwell model and the determinat ion of the relaxation time spectrum from the dynamic moduli data. Further a nalysis of the data at different temperatures confirmed that one of the mod es is possibly related to the lifetime ( similar to 0.01 s at 25 degrees C) of the hydrophobe in the micellar junction and the other to the network re laxation ( similar to 6 a at 25 degrees C). The lifetime is in the same ord er of magnitude as determined by NMR for other associative polymer systems (Petit-Agnely and Iliopoulos, 1999). This is the first experimental verific ation that the lifetime and network relaxation time can be differentiated i n a model HEUR polymer system. (C) 2000 The Society of Rheology. [S0148-605 5(00)00801-4].