The effect of hydrophilic and hydrophobic block length on the rheology of amphiphilic diblock Polystyrene-b-Poly(sodium methacrylate) copolymers prepared by ATRP.

Following our previous investigation on the effect of molecular architecture on the rheology of Polystyrene-b-Poly(sodium methacrylate) copolymers (PS-b-PMAA), we consider here diblock PS-b-PMAA copolymers characterized by a different length of either the hydrophilic or the hydrophobic block. Various copolymers characterized by different PS or PMAA block length have been prepared by ATRP (kinetics is also discussed) and studied from the point of view of their rheological behaviour in water. To the best of our knowledge, this is the first systematic investigation concerning the effect of block length on the rheology of diblock polyelectrolytes. We found that the hydrophobic block length has small influence on the rheology. Surprisingly, the polymers with shortest PMAA blocks yield the strongest gels at high concentration. A simple model based on the classical theories of self-assembly and percolation of amphiphilic polymers has been here developed in order to explain the observed data.