Moldable photo-responsive elastomers from thermoreversible networks formed by triblock copolymer selfassembly

Abstract

Photo-responsive soft materials that retain the responsive optical anisotropy of liq. crystals can serve as mechano-optic actuators for applications that include non-invasively steering fiber optics for biomedical applications. Here we report that reproducible thermoreversible networks are formed by self-assembly of coil-liq. crystal-coil triblock copolymers: the coil (polystyrene) end-blocks phase segregate from the liq. crystal midblock, forming of uniform and uniformly-spaced phys. crosslinks, These polymers are elastic in the melt (at room temp.) and can be easily molded into desired shapes. Starting from identical triblock prepolymers (with polystyerene end blocks and 1,2-polybutadiene midblocks), a matched pair (3% azobenzene, and no azobenzene) of liq. crystal triblock copolymers was synthesized. These triblocks were then blended to prep. a series of elastomers with 0 to 3% azobenzene groups, while matching in nearly all other phys. properties (cross-link d., modulus, birefringence, etc.), and photo-response was quant. measured, allowing us to isolate the effect of concn. of photo-responsive azobenzene groups on photo-response.