Consequences of molecular bridging in lamellae-forming triblock/pentablock copolymer blends

This study demonstrates that bridging (and possibly knotted looping) pentablock configurations in CEC/CECEC (triblock/pentablock) blends play significant roles in the shear-induced alignment and tensile mechanical properties of lamellae-forming block copolymers. Adding just 15 wt% pentablock to the triblock copolymer results in a perpendicular lamellar orientation at all applied strain amplitudes under reciprocating shear, similar to the behavior of the pure pentablock. In contrast, the triblock copolymer exhibits a transition from the perpendicular to the parallel orientation at high strain amplitudes. Approximately 10 wt% pentablock copolymer leads to a dramatic improvement in the strain at failure in shear aligned specimens when the strain is applied normal to the lamellae, a condition that results in brittle failure at small strains with the CEC triblock material. These findings are consistent with calculations that assume pentablock chains bridge the lamellae, thereby reinforcing the brittle C domains.