X‐ray investigations of liquid crystalline homo‐ and copolysiloxanes with paired mesogens

Abstract

X-ray scattering experiments on oriented polysiloxanes with paired mesogens and different distances between these swallow-tailed side groups show a remarkable dependence of the smectic monolayer thickness on the degree of dilution, whereas the interplanar distances of the side groups remain nearly constant. Due to the dominating interaction of the mesogenic moieties, the flexible main chain is forced to take part in the layer formation. A packing model is proposed to explain the results of the X-ray studies. For polymers with five or more dimethylsiloxane copolymer segments, a diffuse scattering appears in the smectic as well as in the isotropic phase. This scattering is independent of the orientation of the samples. It is probably caused by the main chain and has also been observed for the unsubstituted poly(hydrogenmethylsiloxane).

Mechanics of Homeotropically Ordered Smectic‐A Elastomers with Global Oblate Chain Conformation

“…[6] Similar observations could be expected from homeotropically oriented thin elastomer films, produced by photo-crosslinking of a surface aligned S A polymer. However, neither spontaneous shape changes at the smectic-isotropic phase transformation nor a significant impact of the oriented layer structure on the rubber elastic modulus were observed for these materials, [12][13][14][15][16][17] which is in clear contrast to the S A LSCEs presented in this study. For elastomer E1 with the lowest crosslinking density the layer compression modulus B ¼ 1.1 Â 10 7 N Á m À2 is significantly larger than those observed for conventional low molar mass liquid crystals, where B is typically in the order of 1-5 Â 10 6 N Á m À2 for low measuring frequencies.…”

The thioether spacer in liquid crystalline polysiloxanes with cyano- and nitrobiphenyl mesogens

“…The wide angle diffuse band at about 4.6 Å corresponds to the average distance between the mesogenic groups and is characteristic for a disordered smectic phase (A or C) (De Vries 28) ). The diffuse band at about 7.5 Å may be related with the siloxane main chain (Diele et al 29) ). The comparison of the smectic layer thickness d with the length L of the repeating unit of each polymer measured on CPK models with the spacers in all-trans conformation (Tab.…”

Side chain liquid crystal polymers of 2,3‐disubstituted norbornenes via ring‐opening metathesis polymerization, 1 influence of flexible spacer length m = 2 to 12 on the thermotropic behaviour

“…Most of the SCLCP's described in the literature including those prepared by ROMP are just bearing one mesogenic moiety per repeating unit in the polymer. Exceptions are polymers with paired mesogens synthesized by using malonic esters, for example, which are then 0 1995, Hiithig & Wepf Verlag, Zug CCC 1022-1352/95/$10.00 linked to the polymerizable group 13). We found an easy synthetic route to connect two pendant mesogenic moities directly to the polymerizable group namely by employing the (+)-exo, endo-norbornene-2,3-dicarboxylic acid.…”