Self-assembled shape-memory fibers of triblock liquid-crystal polymers

New thermoplastic liquid-crystalline elastomers have been synthesized using the telechelic principle of microphase separation in triblock copolymers. The large central block is made of a main-chain nematic polymer renowned for its large spontaneous elongation along the nematic director. The effective crosslinking is established by small terminal blocks formed of terphenyl moieties, which phase separate into semicrystalline micelles acting as multifunctional junction points of the network. The resulting transient network retains the director alignment and shows a significant shape-memory effect, characteristic and exceeding that of covalently bonded nematic elastomers. Its plasticity at temperatures above the nematic-isotropic transition allows drawing thin well-aligned fibers from the melt. The fibers have been characterized and their thermal actuator behavior-reversible contraction of heating and elongation on cooling-has been investigated.