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| - Molecular Design, Synthesis, and Characterization of LiquidCrystal−Coil Diblock Copolymers with Azobenzene Side Groups
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| - The synthesis and characterization of a family ofwell-defined liquid crystal−coil (LC−coil)diblock copolymers have been carried out. The block copolymers inthis study have been designed tohave nearly identical molecular weight azobenzene-containing LC blocksin order to eliminate possiblevariations in LC behavior caused by the differences in the LC blockmolecular weight. Quantitativehydroboration chemistry was used to convert the pendent double bonds ofan isoprene block to hydroxylgroups to which the mesogenic groups were attached via acid chloridecoupling. The LC homopolymerand the block copolymers (LC volume fraction fromfLC = 0.82 to fLC =0.20) all exhibited smecticmesophases with similar clearing transition temperatures. Theclearing transition enthalpies stronglydepend on the block composition ratio and decrease as the LC blockvolume fraction decreases. Solvent-casting of a lamellar LC−coil copolymer (SICN5-66/60) resulted in anoriented bulk film in which boththe axes of the mesogenic groups and the lamellar interfaces lieparallel to the film surfaces. A LCcylinder morphology was observed with a fLC =0.22 LC-containing block (SICN5-176/55) using TEM andconfirmed by SAXS measurements. This is the first observation withthe LC block in a cylindermicrodomain. Other morphologies (bicontinuous, LC sphere) wereobserved by TEM while retaining thesmectic order in the LC microphase.
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