Main semiflexible

Table 1 Thermal and geometrical data of selected semiflexible polymers giving rise to thermotropic hexagonal mesophases or main-chain disordered crystalline phases (adapted from [11])... 

FIGURE 5.7 Schematic Representation of typical, (partially) electroluminescent LC polymer architectures. (a) Rodlike structure, (b) Hairy-rod structure, (c) Combined main-chain-side-chain system, (d) Semiflexible segmented structure, (e) Semiflexible segmented structure with disklike mesogen. (After Weder, C. and Smith, P., Main-chain liquid-crystalline polymers for optical and electronic devices, in Encyclopedia of Materials Science and Technology, Buschow, K.H., Cahn, R.W., Flemings, M.C., Ilschner, B., Kramer, E.J., and Mahajan, S., Eds., Elsevier Science, New York, 2001.)... 

Figures 7 and 8 display such plots for various lyotropic liquid-crystalline polymer systems, which range in q from 5.3 to 200 nm. As expected, most data points come close to the theoretical curve. This finding suggests that liquid crystallinity of stiff-chain or semiflexible polymer solutions has its main origin in the hard-core repulsion of the polymers.

Investigations in the past years have proved that applying the concept of flexible spacer, polymers can be synthesized systematically, which exhibit the l.c. state. Owing to the flexible linkage of the mesogenic molecules to the polymer main chain, very similar relations can be expected with respect to 1-l.c., like chemical constitution and phase behavior, or dielectric properties and field effects for the l.c. side chain polymers. This will be in contrast to main chain polymers, where the entire macromolecule, or in case of semiflexible polymers parts of the macromolecules, form the l.c. structure. The introduction of a flexible spacer between backbone and mesogenic group can be performed in a broad variety of chemical reactions. Some arbitrarily... 

The main field of polyurethane application is the furniture industry, around 30% of the total polyurethanes produced worldwide is used for the production of mattresses from flexible slabstock foams. Automotive manufacture is the second important application for flexible and semiflexible polyurethanes (seat cushioning, bumpers, sound insulation, and so forth). Rigid polyurethane foams are used in thermal insulation of buildings and refrigerators, cold stores, pipe insulation, refrigerated transport, thermal insulation in chemical and food industries. The polyurethane elastomers are used for shoe soles,... 

Main Chain Liquid Crystalline Semiflexible Polymers... 

Hardouin, F., Sigaud, G., Achard, M. F., Brief A., Cotton, J. P., Yoon, D. Y, Percec, V., and Kawasumi, M., SANS study of a semiflexible main chain hquid crystalline polyether. Macromolecules, 28, 5427-5433 (1995). 

At about 50% (w/w), phase inversion takes place, and at COP concentrations beyond 50% the formation of LC-rich islands in an LC-poor matrix is observed. These islands have been described by several authors in the COP system [118] and in a blend consisting of a rigid rod and a semiflexible coil polymer [121]. The formation of these islands is mainly due to differences in viscosity and surface tension of LC-poor and LC-rich phases and the tendency to achieve efficient packing by orientation and the lowering of lateral distances of the anisotropic parts of a polymer. The LC-poor (= PC-rich) matrix has a higher melt viscosity than that of COP. In a shear field or under... 

The synthesis and some thermal properties of three series of block copolymers comprising both main-chain and side-chain liquid-crystalline (LC) blocks in the same macromolecular structure are described. The former block is a semiflexible LC polyester (block B), and the latter is an LC polymethacrylate (block A) containing a variously substituted mesogenic unit. The two structurally different blocks were partly phase-separated within the glassy and LC states and underwent distinct phase transitions. Significant deviations of the transition enthalpies relative to those of the corresponding homopolymers suggest the occurrence of a more or less diffuse interphase which may depend on the nature of the mesophase formed. 

Fig. 4. Schematic representation of t5rpical EL poisoner architectures, (a) Plain, conjugated main chain, (b) hairy-rod structure, (c) semiflexible, segmented structure, and (d) nonconjugated poljmier with conjugated side chains, tt-conjugated moiety . flexible segment and solubilizing side chain.

The aromatic semiflexible polyesters can be formed by varying the dicarboxylic multi phenyl acid structure (naphthalene and diphenol) and non-linear aromatic diol (3,4 -dihydroxybenzophenone). 3,4 -dihydroxybenzophenone can be synthesized from 4-methoxy bromobenzene and m-methoxybenzonitrile via multistep reaction, which can be condensed with respective diacid chloride in o-dichlorobenzene at reflux temperature [43]. It is well known that dimethyl siloxane spacer can make a flexible/semiflexible LC polymer. Thermotropic flexible liquid-crystalline main chain polyesters... 

Figure 6.30 presents a summary of the different possible structures existing in different temperature regions. The phase transitions are dominantly of first-order type. A relatively common thermal behaviour of semiflexible main-chain and side-chain polymers with long spacers is that a smectic structure is formed directly from the isotropic melt without the appearance of any intermediate nematic phase. The development of a smectic phase requires some axial order of the chain. Statistical main-chain copolymers generally do not possess a smectic mesomorphicity. On cooling, they transform into a nematic glass. 

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