Structure and Dynamics of Blends of Diblock Copolymers

The melt state rheological behavior of a series of blends of a lamellae‐forming nearly symmetrical polystyrene‐polyisoprene (PS‐PI) diblock copolymer with a sphere‐forming highly asymmetrical PS‐PI diblock copolymer is correlated to their structure obtained from small‐angle neutron scattering (SANS). The exponential composition dependence of the relaxation of fluctuations associated with the disordered asymmetrical diblock is similar to that observed in solutions of star polymers. Further, the zero‐shear viscosity of the blends in the disordered state exhibits unusually strong composition dependence. These dynamic properties are closely linked with the SANS‐based structural data that suggest strong compositional fluctuations, even in the disordered state.