Role of molecular architecture in mechanical failure of glassy/semicrystalline block copolymers: CEC vs CECEC lamellae

The role of molecular architecture on the ultimate mechanical properties of nearly symmetric, lamellae-forming, CEC triblock and CECEC pentablock copolymers, where C and E denote poly(cyclohexylethylene) (PCHE) and poly(ethylene) (PE), respectively, was studied. Reciprocating shear was exploited to produce macroscopic sheets of aligned material with a "perpendicular" orientation. Subsequent stress-strain measurements, directed normal to the lamellae, revealed dramatic differences in toughness that correlate with architecture. Results demonstrate a dramatic crossover from brittle to ductile behavior when block connectivity is increased from n=2 to n=4, where n signifies the number of linearly coupled triblocks.