The synthesis and the phase behaviour of liquid crystalline main chain polymers are described. In these poly- and copolyesters the mesogenic units are linked by highly flexible oligodimethylsiloxane spacers. The comparison of their phase behaviour with that of polyesters known from the literature shows that dimethylsiloxane spacers as a replacement for alkyl spacers are leading to a drastic decrease of the transition temperatures. Depending on the length of the spacer glass transitions as low as −111°C can be achieved. The widths of the liquid crystalline phases thereby are retained up to a spacerlength of 13 oxydimethylsilanediyl (dimethylsiloxane) units. The homopolyesters mainly show sme…

Etude de deux systemes differents avec de l'hydroxy-4 benzoate de phenyle comme unite mesogene. Les separateurs sont formes de 6 unites methylene et le squelette est de l'acide poly(meth)acrylique

Study of the micro-phase separation in LC-polymers with paired mesogens

Differential scanning calorimetry and miscibility investigations were used to study the micro-phase separation of liquid-crystalline dimesogenic side-group polysiloxanes. Diluted co-polysiloxanes exhibit two glass transition temperatures and an unusual miscibility behavior. The observed biphasic character is compared with that of certain amphiphilic systems.

Polyhydrogenomethylsiloxanes ayant la meme paire de groupes lateraux mesogenes mais un bras ecarteur different

Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR

The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the …

The molecular order and mobility of two liquid-crystalline polyacrylates with phenyl benzoate moieties as mesogenic side groups and (CH2)m spacers (m = 2 and m = 6) were investigated by pulsed 2H NMR. The mesogenic side groups were isotopically labelled at the terminal phenylene ring. In the glassy state the orientational distribution function was characterized from the angular dependence of the 2H NMR line shape of samples macroscopically ordered in their nematic phase by the 8,4 T magnetic field of an NMR spectrometer. It was found to be Gaussian with widths of ± 18,5° and ± 10,5° for the m = 2 frozen nematic and m = 6 frozen smectic system, respectively. The phenylene rings undergo 180° …

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 distance 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 o…

Structure and Dilution of Mesogenic Side Chains in Liquid Crystalline Polysiloxanes

Abstract The structure of the smectic phases in four series of homo- and copolymers based on dimethylsiloxane chains with a definite variation of the concentration of the paired mesogenic side chains has been investigated by means of X-ray methods. The dilution of the mesogenic moiety was achieved by insertion of additional dimethylsiloxane segments. A nearly linear dependence of the layer spacings on the dilution has been found. A model of the structure is proposed which consists of two sublayers one of which contains the irregularly arranged main chain whereas the other one is formed by the side chains.