Liquid crystalline polymers spacer group

Liquid crystalline main chain polymers with siloxane spacer groups were obtained by the hydrosilation of (Si—H) terminated polydimethylsiloxane oligomers and mesogenic groups with terminal double bonds as shown in Reaction Scheme XVII-(a). Reactions were usually carried out in THF with the Wacker Oil catalyst 255). Completion of the reactions was followed by the disappearance of the strong (Si—H) absorption band at 2140 cm-1 using IR spectroscopy. 

Polymers with flexible spacer groups. Polymers obtained by precipitation or by casting films from solutions were found to be amorphous as shown by X-ray and microscopical observations. The DSC data revealed that on heating up the samples for the first time a stepwise increase of the specific heat occurred which could be attributed to a glass transition. Thus at room temperature the as received samples were in the isotropic glassy state, apparently no liquid crystalline solutions exist. 

Polymers without flexible spacer groups. The DSC curves of t he polymer 3 indicated the existence of a liquid crystalline glassy state at room temperature. The polymer was found to be smectic. Two melting peaks were observed in the temperature range between 300 and 310 deg. C. These peaks are not as easily observed as in the case of the polymers discussed above, since the decomposition takes place in the same temperature range. The occurrence of exothermic peaks on cooling nevertheless indicates that reversible melting and crystallization processes take place. 

Polymers with flexible spacer groups. Smectic or nematic polymers were obtained depending on the nature of the substituent R in the case of polymers 1 (Table 2). It has to be pointed out that the structures at temperatures above the glass transition temperatures are equilibrium structures, since thermodynamically stable liquid crystalline phases exist. This is in contrast to most systems studied until now where only liquid crystalline structures were obtained ... 

Kiihnpast. K., Springer, J.. Scherowsky. G., Giesselmann, F. and Zugenmaier, R, Ferroelectric liquid-crystalline side group polymers spacer length variation and comparison with the monomers, Liq. Cry.st., 14, 861-869 (1993). 

In summary the results of our 2H NMR investigation illustrate the spacer model for liquid crystalline polymers, indicating, however, that the decoupling of the mesogenic groups from the main chain, while effective, is not complete. 

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl-1,4-phenylene oxide) (PPO) containing pendant mesogenic units separated form the main chain through spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium co -(4-oxybiphenyl) alkanoates and potassium u-(4-methoxy-4-oxybiphenyl)-alk.an oates. While PPO required ten methylene units as a spacer and 4,4 -methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism,... 

In order to determine the necessity and/or the length of the spacer that is required to achieve liquid crystalline behavior from flexible vs. rigid polymers, we have introduced mesogenic units to the backbones of a rigid [poly(2,6-dimethyl-l,4-phenylene oxide) (PPO)] and a flexible [poly(epichlorohydrin) (PECH)] polymer through spacers of from 0 to 10 methylene groups via polymer analogous reactions. 

Large numbers of functionalized LB films have been prepared. Highly ordered LB films have been formed by the inclusion of surface-active cobaltous phthalocyanine [168] amphiphilic TCNQ was assembled to function as conducting LB films [169] liquid-crystalline LB films, potentially capable of undergoing thermotropic or lyotropic phase transitions [170, 171], have also been generated. Spacer groups introduced into polymeric surfactants (23) helped to stabilize the LB films which they formed by decoupling the motion of pendant polymers (see Fig. 13) [172]. 

Thus, the remoteness of mesogenic groups from the backbone provided by a polymethylene spacer secures them sufficient autonomy from the main chain. On the other hand, the fact that mesogenic groups are chemically linked with the main chain of the macromolecule assists their cooperative interaction. This is why comblike polymers have come to be accepted as convenient matrices for constructing LC polymers. Already a few hundred liquid-crystalline polymers with various mesogenic side groups have been synthesized. 

It should be emphasized that these features of the transition between coil and liquid-crystalline globule, as well as the expression (3.7) for the temperature of this transition, are not sensitive to the specific polymer chain model in the limits p S> 1 and N > 1. In particular, the above results remain valid for each of the models shown in Fig. 7b-d, i.e. the chain composed of rods connected by flexible spacers (Fig. 7 b), the flexible chain with the rodlike side groups (Fig. 7 c) and the persistant chain (Fig. 7d). Such universality can be proved by means of the following simple arguments. 

Gangadhara et al. have linked the cyanobiphenyl mesogen via a dicarbox-imide-group to an oxanorbornene ring system Vl-n, n=2-8 (see Fig. 4). Polymerization was carried out with Schrock type initiator 4. The dicarboximide linkage probably hindered the formation of LC phases even the introduction of relatively long spacers between the polymer backbone and the mesogen did not lead to liquid crystalline monomers or polymers [41]. 

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