Self-Assembly of Flexible–Semiflexible–Flexible Triblock Copolymers

Abstract

The self-assembly of ABA triblock copolymers comprising flexible amorphous poly(ethyl methacrylate) (PEMA, A block) and semiflexible liquid crystal (LC) polyester (B block) was investigated for amorphous block volume fractions (φ) ranging from 20% to 80%. Two copolymer series with different LC block molecular weights (Mn,LC) were examined. At φ < 55%, block copolymers with Mn,LC = 11 600 formed lamellar microdomains in which LC segments mostly extended along the lamella normal but folded to fit in the lamellae. When φ was augmented, the LC segment fold (Nfold) increased to enhance the interface between the LC and amorphous segments and counterbalanced the increase in amorphous lamella thickness by reducing the LC lamella thickness. When φ > 68%, the LC lamellae were divided into cubes, transforming into spheres in the PEMA matrix. When Mn,LC decreased to 6300, the copolymers showed similar morphology. However, the lamellae adopted zigzag configurations showing a greater tilting angle between the lamella normal to the LC chain axis with increasing φ. Thus, the LC and PEMA segments enhanced their interface by mutually sliding along the chain axis instead of increasing Nfold.