Phase Behavior of Polylactide-Based Liquid Crystalline Brushlike Block Copolymers

We explore the morphology and phase behavior of a recently introduced architecture of liquid crystalline brushlike block copolymer (LCBBC) as functions of composition and molecular weight. Low-polydispersity materials were prepared by ring-opening metathesis polymerization of n-alkyloxy­cyano­biphenyl and poly­(dl-lactide) (PLA) functionalized norbornene monomers. Well-ordered block copolymer mesophases were observed with transitions from spheres to hexagonally packed cylinders, lamellae, inverse cylinders, and inverse spheres on increasing the weight fraction of the liquid crystalline block, f_LC, from 0.15 to 0.85. The microdomain spacing displays a power-law scaling with molecular weight with an exponent of 0.6, L₀ ∼ MW^0.6. The simple occurrence of microdomains with curved interfaces, spherical and cylindrical, and the sublinear scaling of microdomain spacing with molecular weight set this system clearly apart from bottlebrush block copolymers. We observe a peculiar morphology dependence of the liquid crystal anchoring condition with the cyanobiphenyl mesogens adopting planar anchoring at cylindrical microdomain interfaces while both homeotropic and planar anchoring were displayed at the block interface in lamellar systems.