Thermal Behaviour of Cyclic Oligosiloxanes
229=[1271]
decreasing glass transition temperatures depend on the size of ring of course,
but also on the molecular weight of the mesogenic groups (Figs. 5–6).
So, in the case of cinnamic esters in mesogenic core, the glass transition
temperatures increase with increasing size of the siloxane backbone.
By linking the siloxane ring to the mesogenic group with phenyl
benzoate in core, decreasing glass transition temperatures are observed
with increasing number of Si atoms in the siloxane ring.
A similar result was also observed with the changes of spacer length. The
increasing number of C-atoms in the spacer length yields an increase in
glass transition temperatures (O4M1–O4M3 or O6M1–O6M3) in contrast
with the linear LC siloxane polymers [15].
The influence of the size of the siloxane ring on the distances of SmA or
SmCꢀ layers is relatively weak.
CONCLUSIONS
Three series of new side chain cyclic oligosiloxanes based on different
mesogenic rigid cores with chiral end group have been synthesized and
characterized. All of them exhibited enantiotropic smectic mesophases
with monolayer structure. In particular, cyclic oligosiloxanes with cinna-
moiloxyphenyl rigid core and (S)-2-methylbutyl chiral moiety display chiral
smectic C mesophase, whereas the series with 4-benzoiloxyphenyl in meso-
genic core form monolayer smectic A mesophase. Oligomers substituted by
biphenyl of chiral chloroacids exhibit two liquid crystalline phases: chiral
smectic C and smectic A.
REFERENCES
[1] McArdle, C. B. (1989). In: ‘Side Chain Liquid Crystal Polymers’, Blackie and Son Ltd.,:
Glasgow, 395.
[2] Collyer, A. A. (1992). Liquid Crystal Polymers, (Elservier, London).
[3] Goodby, J. W. (1991). In: Ferroelectric Liquid Crystals – Principles, Properties and
Applications, Gordon and Breach: Philadelphia and Reading, 91.
[4] Simmons, D. J. (1992). In: Liquid Crystal Polymers from Structures to Applications,
(Elsevier, London), 349.
[5] Eberle, H. J. Miller, A., & Kreuzer, F. H. (1989). Liq.Cryst., 5, 907.
¨
[6] Kreuzer, F. H., Andrejewski, D., Haase, W., Haberle, N. Riepl, G., & P. Spiess, (1991).
Mol. Cryst. Liq. Cryst., 199, 345.
[7] Bunning, T. J., Klej, L. H. E., Samulski, E. T., Drane, R. L., & Linville, R. J. (1991). Liq.
Cryst., 10, 345.
´
[8] Białecka-Florjanczyk, E., Orzeszko, A., Sledzinska, I., & Gorecka, E. (1999). J. Mat.
´
´
ꢀ
Chem., 9, 371.
[9] Schacht, J., Baethage, H., Giesselmann, J., & Zugenmaier, P., (1998). J. Mat. Chem., 8,
603.