Phase behavior and rheological properties of aqueous solutions containing mixtures of associating polymers

The phase behavior and the rheological properties of aqueous solutions cont aining mixtures of multiblock hydrophobically modified polyacrylamides (HMP AM) have been investigated, Mixtures of a HMPAM with a homopolyacrylamide ( PAM) phase separate above a given overall polymer concentration and a given PAM content. These results are in qualitative agreement with the predictio ns of a model based on the entropy changes due to the associations between the hydrophobic units [Annable, T.; Ettelaie, R. Macromolecules 1994, 27, 5 616]. The viscoelastic behavior of semidilute solutions of various series o f copolymer mixtures with variable molecular weights (M-w approximate to 10 (5) to 2 x 10(6)), hydrophobe contents ([H] = 0.5-2 mol %), and hydrophobic block lengths (N-H approximate to 2-7 units per block) has been studied us ing steady-flow and oscillatory experiments. The linear viscoelasticity can be described by a slow relaxation process and other faster complex relaxat ion processes. When both HMPAM are mutually entangled, the slow relaxation is in agreement with the expectation from a hindered reptation model with i n particular a plateau modulus that only depends on polymer concentration. When the two HMPAM are unentangled, the behavior is more complex, the prope rties being strongly dependent on the hydrophobe characteristics of the two copolymers. In particular, when there is a strong mismatch between the hyd rophobic parameters, the viscosity of the system is depressed likely due to a local segregation between the two copolymers.