Side chain mesogenic

Lastly, it was demonstrated with PPO substituted with a series of alkyl side-chains as we have here, that the glass transition temperature decreases with an increase in the side-chain length (28). At the same time, the Tg s of the more flexible side-chain liquid crystalline polymers investigated to date are always much higher than those of the corresponding polymers without the mesogenic side-chains (3). Therefore, it is quite likely that we may obtain side-chain liquid crystalline polymers of approximately the same Tg from PPO and PECH. 

Earlier studies of macromolecules with flexible, non-mesogenic side-chains had revealed that the transition properties change with increasing side-chain length from typical polymeric behavior to that of the small molecule which corresponds to the side chain 72,73). With short side-chains and proper backbone geometry (tacticity),... 

In addition to their unusual rheological properties, the nematic phases of polymers, like those of simple compounds, can be oriented by the application of magnetic or electrical fields. These properties have been more fully examined for comb-type polymers with mesogenic side-chains than for polymers with the mesogenic groups in the main chain, since in the comb polymers it is possible to influence the side-chain orientation independently of the main-chain orientation. 

While for m-l.c. s the state of order is only determined by the anisotropic interactions of neighbouring molecules, for the polymers additionally a disturbing effect of the backbone via the flexible spacer on the anisotropic order of the mesogenic side chains is to be expected and vice versa. Therefore it is of interest to investigate whether... 

When the dye molecules are dissolved in the p-l.c. M3, where the chemical structure of the mesogenic side chains is very similar to the structure of the 1-I.c., another result for S is obtained (Fig. 14). It is obvious, that the temperature dependence of S corresponds to the temperature dependence of the monomer system M2, whereas the absolute value of S is lower. If we determine S at the reduced temperature T = 0.95, we find S = 0.54. This value is reduced by about 10% compared to the I-l.c. 

From these experiments we can conclude that the length of the flexible spacer has no measurable influence on the orientational long range order of the mesogenic side chains. If on the contrary l-l.c. s are attached to the polymer backbone, the state of order is reduced. 

While for nematic polymers the statistical distribution of the centers of gravity of the mesogenic side chains is compatible with a more or less statistical main chain conformation, for smectic polymers a three dimensional coil conformation is no longer consistent with the layered structure of the mesogenic side chains. The backbone has to be restricted in its conformation, which will cause a more pronounced interaction between the main chain and the anisotropically ordered mesogenic side chains, compared to nematic and cholesteric polymers. 

In any case, both models have in common that owing to the positional ordering of the mesogenic side chains, the polymer backbone no longer exhibits a statistical three dimensional coil conformation. Therefore at the phase transformation isotropic to smectic or nematic (cholesteric) to smectic, in addition to the change of the anisotropic packing of the side chains, the main chain has to change its conformation, which must be consistent with the layered smectic structure. A direct interaction... 

These examples clearly indicate that the extent of the l.c. phase of the polymer is mainly influenced by the flexibility of the polymer main chain, determined by its chemical constitution. The flexibility of the backbone also influences the mobility of the mesogenic side chains. 

The thermodynamic investigations have indicated that the glass transition is a freezing-in process. Consequently the anisotropic liquid crystalline orientation of the mesogenic side chain should also freeze in, yielding an anisotropic glass having a liquid crystalline structure. This process is of interest in view of the applicability of l.c. polymers. 

The schema in Fig. 37 a indicates the synthesis route for elastomers. It is most convenient to start with well characterized linear l.c. side chain polymers, which additionally contain reactive centers. These centers may be located within the polymer backbone or as substituents of the mesogenic side chains. In a suitable reaction, or... 

We will discuss some preliminary results, which have been performed recently l01). In Fig. 39a the results for polymer No. 2d of Table 10 are shown, which were obtained by torsional vibration experiments. At low temperatures the step in the G (T) curve and the maximum in the G"(T) curve indicate a p-relaxation process at about 120-130 K. Accordingly the glass transition is detected at about 260 K. At 277 K the nematic elastomer becomes isotropic. This phase transformation can be seen only by a very small step in G and G" in the tail of glass transition region, which is shown in more detail in Fig. 39 b. From these measurements we can conclude, that the visco-elastic properties are largely dominated by the properties of the polymer backbone the change of the mesogenic side chains from isotropic to liquid crystalline acts only as a small disturbance and in principle the visco-elastic behavior of the elastomer... 

These experimental results give only a first insight into the fascinating properties of these very new l.c. elastomers. Further detailed studies have to come to a more profound understanding of the interactions of polymer networks and l.c. order of the mesogenic side chains. The exceptional photoelastic and thermoelastic properties promise to open up a new scientific and technological field of interest. 

The liquid phase synthesis on PEG has also been used for the conformational analysis of collagen-like sequences by CD studies 237). The attachment to PEG has also permitted the CD spectral delineation of the specific interactions between the polypeptide chains and sidechain groups 238,239). Thus, Anzinger et al. observed that onset of local ordered structures in the mesogenic side chains of polylysine blocks attached to PEG leads to significant, specific alteration in the backbone conformations of the peptide chain 239). 

Hydrogen-Bonded Comb Copolymers Mesogenic Side Chains. 157... 

Several theoretical works predict the onset of mesophases (1-5) and take into account the molecular structure of polymers. There are two kinds of structures that are often cited the rigid or semi-rigid linear polymers and the connected ones or those containing mesogenic side chains ( ). 

This can be explained by the fact that in a polymer molecule (Fig. 78b) the longitudinal components of monomer unit dipoles mh are mutually compensated and the main part in the observed EB is played by normal components of monomer unit dipoles, mi, which can be parallel to the main chain of the macromolecule owing to its comb-like structure. In other words, in molecules of comb-like polymers containing mesogenic side chains, the orientations of the Mi components of the side group dipoles are correlated with each other. As a result, the macromolecule as a whole or part of it can exhibit a considerable dipole moment m in the direction of the main chain L (Fig, 78b). The existence of this dipole accounts for the orientation of the main chain in the field direction leading to negative EB. 

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