Influence of Defect Density on the Rheology of Ordered Block Copolymers

Quiescently ordered block copolymer materials contain randomly oriented grains with concomitant defects and grain boundaries. Current theories suggest that the anomalous rheological properties of block copolymers are related to the average grain size, i.e. defect density. We present rheological data from a concentrated solution of a polystyrene−polyisoprene diblock copolymer in dioctyl phthalate (70 wt % polymer). The sample has a cylindrical morphology in the ordered state. The average grain size was changed by over an order of magnitude (0.4 to 7.4 μm) by adjusting thermal history. The viscoelastic moduli of this material in the frequency range 10 -2 −10 2 rad/s were, however, not significantly affected by this change.