Side-chain liquid crystalline polymers models

A simple hybrid model for a siloxane side-chain liquid crystalline polymer is shown in figure 4. Here, the methylsiloxane backbone and the flexible alkyl spacer of the real polymer have been replaced by a series of united atom potentials, and the mesogenic groups have been replaced by Gay-Beme [16] potentials. 

Figure 5. Cooling of a model side chain liquid crystalline polymer from am isotropic polymer melt. Top absence of an aligning p>otentiad. Middle in the presence of an external aligning potential with = 0.2 kJ mol . Bottom in the presence of an externad aligning potentiaJ with e = 0.5 kJ mol. ...

New approaches and techniques have been proposed to characterize peculiar aspects of L.C. phases or amphiphilic-based systems. The director reorientation of a side-chain liquid crystalline polymer was observed under extensional flow using a 4-roll mill placed in the magnet of a NMR spectrometer. A steric obstruction model was proposed to predict charge-induced molecular... 

Another typical model LCP is PI-14-5CN. It is a nematic side-chain liquid-crystalline polymer (SCLCP), with thechemical structure [54]presented in Figure 11.3. 

Lee, K.-J. Hsiue, G.-H. Wu, J.-L. Sha, Y.-A., Molecular Structure of Side-Chain Liquid Crystalline Polysiloxane in the Smectic C Phase from X-Ray Diffraction and Molecular Modeling Polymer 2007,48,5161-5173. 

Anthamatten M and Hammond P T (2001) Pree-energy model asymmetry in side chain liquid crystalline block copol5rmers, J Polym Sci B Polym Phys 39 2671-2691. 

An interesting area, which involves chiral liquid crystal properties, is that of temperature sensors, used, for example, in the diagnosis of skin cancer, as well as in peripheral blood circulation problems. Another application in the medical field is represented by nematic elastomer films or fibers of liquid crystalline polymers with mesogene in the side chain, that can be used in the manufacture of muscle prosthesis [28]. To optimize their performance for different applications, the current knowledge on the relationship between the structure and properties of liquid crystals should be extended. In addition to further development of liquid crystals and their applications, the liquid crystal theories represent a sound basis for other areas of interest. For example, liquid crystals can be used as model compounds for the study of molecular interactions and of their effects on self-organization in supramolecular chemistry. 

With these three different examples it has been demonstrated that the systematics observed for the polymorphism of m-l.c. s is also valid for the side chain polymers, provided that a flexible spacer connects the rigid mesogenic moieties to the polymer main chain. Deviations from this behavior are observed, when the mesogenic moieties are directly linked to the backbone. Under these conditions, normally no liquid crystalline behavior is to be expected, according to the model considerations mentioned in Chap. 2.1. Some examples, however, proved l.c. properties for such systems, which are characterized by two striking properties Very high glass transition temperatures and only smectic structures even in case of short substituents... 

Fig. 31. Schematic model of the smectic structure of these liquid crystalline side chain polymers...

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. 

Polymers with side anisodiametric groups modeling the molecular structure of low-molecular liquid crystals csm be obtained either through synthesis of monomers with liquid crystalline (mesogenic) groups with subsequent polymerization or throui chemical attachment of molecules of low-molecular liquid crystalline compounds to a polymer chain by way of polymer-analogous transformations. As can be inferred from the bulk of works dealing with this problem, at present, the first of these two methods is used in most cases. 

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