Phase separation and self-assembly of cyclic amphiphilic block copolymers with a main-chain liquid crystalline segment

Abstract

A series of linear and cyclized amphiphilic block copolymers consisting of poly(acrylic acid) (AA_m) and main-chain liquid crystalline (LC) poly(3-methylpentamethylene-4,4′-bibenzoate) (BB_n) segments were newly synthesized. Solid state morphology was investigated by X-ray scattering. Linear AA₂₁BB₉AA₂₁, cyclic AA₃₃BB₁₀, and cyclic AA₅₁BB₁₈ formed lamellar microdomains, where the BB_n segment of cyclic AA₅₁BB₁₈ formed a smectic CA phase. On the other hand, cylinder-type microdomains were formed by linear AA₄₄BB₉AA₄₄ and cyclic AA₁₀₀BB₉. These amphiphilic block copolymers were self-assembled in water to form vesicles or cylindrical micelles, depending on the polymer concentration of the initial THF solution. The response of these nanostructures against an electric field demonstrated that the vesicles formed from linear AA₂₅BB₁₄AA₂₅ and cyclic AA₅₁BB₁₈ turned into substantially larger aggregates, likely due to the reorganization of the LC segment in the bilayer.