Rm. Richardson et al., Liquid crystalline dendrimer of the fifth generation: From lamellar to columnar structure in thermotropic mesophases, LIQ CRYST, 26(1), 1999, pp. 101-108
The structure of a liquid crystalline (LC) carbosilane dendrimer of the fif
th generation bearing 128 terminal cyanobiphenyl mesogenic groups has been
studied. This dendrimer was synthesized by a hydrosilylation reaction and t
hen the cyanobiphenyl mesogenic groups were chemically linked to the dendri
tic matrix via a -OOC-(CH2)(10)-Si(CH3)(2)OSi(CH3)(2)- spacer. Structural s
tudies carried out by polarizing optical microscopy, differential scanning
calorimetry and X-ray diffraction methods revealed unusual phase behaviour.
Ar room temperature the dendrimer forms a lamellar (smectic A) phase which
develops in-plane ordering above 40 degrees C. This is due to a tendency t
o form columns of molecules which are probably perpendicular to the layers.
Above 121 degrees C the material transforms into another more disordered m
esophase which is probably a disordered hexagonal columnar phase. The propo
sed structures and molecular packing in these different types of mesophase
are discussed.