Architecture-induced microphase separation in nonfrustrated A-B-C triblock copolymers

The extent of block microphase separation in nonfrustrated A-B-C triblock copolymers forming a "three-domain, four-layer" lamellar morphology is examined. Specifically, the extent of separation between the B and C blocks is probed, for the case where the B and C blocks are sufficiently compatible that they would not be microphase-separated if they were connected as a diblock. However, attachment of the A block, and consequent localization of the A-B block junction to the A-B lamellar interface, induces extensive separation between the B and C blocks. This separation is revealed both through the small-angle X-ray scattering pattern in the melt, and by distinct glass transitions observed in the solid state for the B block at low B-C segregation strengths, and for both the B and C blocks at higher segregation strengths. The particular polymers studied here have polyethylene as the A block; except for the most weakly segregated triblock, upon cooling from the melt, crystallization of the polyethylene block is confined within the lamellar structure established in the melt, with the polyethylene crystals stacking orthogonally to the microdomain lamellae.