Liquid-Crystalline Polymer Gels

Polymer gels having a liquid-crystalline structure were prepared, and their anisotropic properties were investigated. This study is the first attempt to prepare synthetic polymer gels that possess liquid-crystalline order. These polymer gels showed several anisotropic characteristics.
Polymer gels with cholesteric liquid-crystalline (CLC) order have been prepared by crosslinking lyotropic liquid crystals of poly(��-benzyl L-gultamate) (PBLG) using several diamino compounds of different chain types as crosslinkers in three different solvents. A PBLG/triethylenetetramine/dioxane mixture was found to be the best system to maintain the original cholesteric order. The gels having a CLC order showed the reversible volume change and the cholesteric- -isotropic transition at the helix-coil transition region of PBLG by change of solvent or temperature. Optical anisotropy of CLC gels doped with a variety of dye molecules was also investigated. The CLC gels can reversibly bind dye molecules with specific orientation. Rod-like dye molecules such as azobenzene derivatives with long alkoxy groups showed positive induced circular dichroism, indicating a preference of parallel orientation to the helix of PBLG.
PBLG gels having nematic liquid-crystalline (NLC) order were prepared under a magnetic field. The NLC gel showed a reversible anisotropic swelling and shrinking depending on solvent compositions.The liquid-crystalline elastomers carrying cyanobiphenyl side groups were synthesized by radical copolymerization of 6-(4�f-cyanobiphenyl-4-yloxy)hexylacrylate and hexamethylene diacrylate. The elastomer was swollen in a low molecular weight liquid crystal such as 4-cyano-4'-hexyloxybiphenyl. Swollen elastomer in the nematic phase quickly deformed by application of the DC voltage.