Molecular control of the viscosity of model dendritically branched polystyrene solutions: From polymeric to colloidal behavior

We explore the concentration dependence of the zero shear viscosity of well-defined dendritically branched polystyrene solutions in relation to their internal structure. Whereas in the past the change of total molecular weight was achieved via change of the number of generations (G) for fixed backbone segment length (average number of units between branches, P), these unique materials with constant number of generations allow monitoring the molecular weight through variation of P. We find that increasing P yields polymer-like behavior, whereas for lower backbone molecular weights a predominantly colloidal particle-like behavior is observed. Our results further indicate that the static properties (the branching ratio, i.e., the ratio of dendritically branched-to-linear polymer radius of gyration, g = <R-g(2)>/<R-g(2)>(linear) and scattering intensity) are also sensitive, but to a lesser degree, to the crossover from colloidal to polymeric behavior, especially for the largest molecular weights.