Relationships between Diffusion and Viscoelasticity of Associative Polymer Networks

Hydrophobically ethoxylated modified urethane (HEUR) form the flower micelles and transient network structures through the aggregation of end groups depending on the polymer concentration. The HEUR networks show the viscoelastic relaxation which is described by the Maxwell model. Although there have been many attempts to understand and predict the molecular mechanism, the full understanding remains incomplete. To understand the relaxation mechanism of associative polymers, we measured the linear viscoelasticity and the diffusibility using the fluorescence recovery after photo-bleaching method. With increasing the polymer concentration, the self-diffusion coefficient decreased, while the relaxation time increased, suggesting that the viscoelastic relaxation is correlated with the diffusion of the polymers. The calculated diffusion distance of the HEUR chains within the viscoelastic relaxation time is 100 times larger than the size of a HEUR chain. This significant deviation suggests that some of the HEUR chains diffuse quickly through the unimer and flower micelles at low concentrations and through the recombination process of the network strands at high concentrations.