Start-up shear flow of a well-characterized entangled H-polymer

We present a systematic investigation of the linear viscoelasticity and nonlinear start-up shear flow response of a well-characterized H-polystyrene, an archetype branched polymer. The Branch-on-Branch (BoB) model describes the linear response well, as well as the nonlinear transient response at lower rates, in the regime where finite extensibility effects do not seem to be important. The data reveal shear thinning similar to that of comb polymers and a broad transient overshoot of the shear stress growth coefficient, which suggests a coupled response of backbone and branches. The rich features of the data and comparison with the BoB-model should provide a useful framework for further exploring the transient molecular response of branched polymers in complex flows.