ABC Heterotelechelic Associative Polyelectrolytes. Rheological Behavior in Aqueous Media

A polystyrene−poly(sodium acrylate)−poly( n -butyl methacrylate) (PS−PANa−PnBMA) ABC triblock copolymer was synthesized by sequential anionic polymerization and modification of the poly( tert -butyl acrylate) middle block by selective hydrolysis and neutralization to its ionic functions. Because of the fact that both outer hydrophobic blocks are very short comparable to the middle one, this polymer can be viewed as a “heterotelechelic” polyelectrolyte. The rheological behavior of the PS−PANa−PnBMA aqueous solutions was explored by steady state and oscillatory shear flow measurements. Dilute solutions ( c < 1 wt %) exhibit very high viscosity, showing that these kinds of polymers can be used as effective thickeners. This behavior is attributed to the formation of a transient network constituted from PS and/or PnBMA physical cross-links interconnected by stretched polyelectrolyte chains. An unusual observation is that the viscosity of the system seems to be invariant over a wide temperature range. Finally, the differences between heterotelechelic and telehelic polyelectrolytes of the type PS−PANa−PS are also discussed.