Gradient and block side-chain liquid crystalline polyethers

Abstract

A set of gradient copolymers composed of liquid crystalline polyether and poly(butylene oxide) with narrow molecular weight distributions and well-defined, continuous growing composition profiles were synthesized via anionic ring-opening polymerization. For comparison, the corresponding diblock copolymers without a compositional gradient were also prepared. The thermal transitions, phase structures and the evolutions of these two sets of liquid crystalline copolymers with composition and temperature were systematically investigated. The compositional gradient copolymers were found to possess a remarkable sensitivity on the phase structures on multiple length scales. Compared with the corresponding liquid crystalline block copolymers, they exhibited a broad glass transition region and a large breadth of liquid crystalline phase transformation associated with disordered mesogenic packing and a thickness distribution of liquid crystalline layers. Ordered, nanophase separated structures were observed to gradually develop with an increase of gradient length. They exhibited distinct ordering and evolution processes with continuous liquid crystalline melting, which are different from the reference samples of diblock copolymers. Those behaviors are speculated to originate from the heterogeneity intrinsic to the liquid crystalline gradient copolymer.