J. Newton et al., SYNTHESIS AND PROPERTIES OF LOW-MOLAR-MASS LIQUID-CRYSTALLINE SILOXANE DERIVATIVES, Journal of materials chemistry, 4(6), 1994, pp. 869-874
A number of liquid-crystalline siloxane derivatives based on the 4-(om
ega-alkenyloxy)-4'-cyanobiphenyl mesogenic unit have been prepared and
their phase-transitional properties characterised. The compounds were
synthesized by the addition of the 4-(omega-alkenyloxy)-4'-cyanobiphe
nyl moiety to pentamethyldisiloxane catalysed by a platinum divinyltet
ramethyldisiloxane complex. The materials are denoted ABs where A refe
rs to the number of methylene groups in the 4-(omega-alkenyloxy)-4'-cy
anobiphenyl and B refers to the number of silicon atoms in the siloxan
e unit. With the exception of 3/2 and 4/2, which exhibit only monotrop
ic phase transitions, all these materials exhibit an enantiotropic sme
ctic A phase. Preliminary X-ray results also support this. The thermal
properties of this new series of thermotropic liquid-crystalline silo
xanes were studied by differential scanning calorimetry (DSC) and pola
rising microscopy. The transitional properties for the AB series exhib
it a pronounced odd-even effect with the length of the alkyl segment.