Rigidity, main chain

The PPhE bearing the PBE dendron as the repeating side chains is also soluble in THF, whereas the rigid main chain itself does not dissolve in any solvent. The blue-luminescence dendron-grafted rigid polymer forms thin films by spin coating [18]. 

Dinner, A.R. Local deformations of polymers with nonplanar rigid main-chain internal coordinates. J. Comput. Chem. 2000, 21, 1132 14. 

Unusual properties of fully aromatic polyesters are observed if they have at least partially a rigid planar chain structure. In particular, they can form thermotropic liquid crystalline states (see Example 4-5). As already discussed in Sect. 1.2.4 an important structural prerequisit for LCPs of Type A in order to attain the liquid crystalline state of aromatic polyesters (and aromatic polyamides, see Example 4-14), is a rigid main chain according to the following construction principle ... 

Despite their attractive properties, no clear application for thermotropic polymers of the rigid main-chain types has yet emerged. Fibre manufacture is an obvious... 

Regarding the chemical constitution of these monomers, the polymerizable, functional group was always directly linked to the rigid, voluminous mesogenic moieties. As space filling models indicate, polymers result, having a rigid main chain. This... 

Although many stereoregular polymers have a helical conformation in the solid state (5,96], the conformation is lost in solution in most cases, except in the case of some polyolefins with optically active side groups [12], because the dynamics of the polymer chain are extremely fast in solution. Therefore, isotactic polystyrene [15,16] and polypropylene [17] prepared with an optically active catalyst do not show optical activity due to a helical conformation. However, a helical conformation can be maintained in solution for some polymers having a rigid main chain or bulky side groups that prevent mutation to random conformation, and the conformation may... 

K. Beppu, Y. Kaneko, J-I. Kadokawa, H. Mori, T. Nishikawa, Polymer J., 2007, 39(10), 1065-1070. Synthesis of sugar-polysiloxane hybrids having rigid main-chain and formation of their nano aggregates ... 

Main Chain LC Polymers. New thermotropic copolyesters with either random or ordered mesogenic sequences have been reported with a wide range of mesophase behaviors. Recent developments in this field have included the use of naphthalene, stilbene and related structures in addition to the traditional phenylene groups to produce the required rigid main chain, and these are described in chapters by Jin, Jackson and Morris, and Skovby et al. Efforts have been undertaken to control transition temperatures and solubility through the use of either substituents or changes in the monomer sequence distribution. Successful application of these efforts have led to the commercialization of several thermotropic aromatic copolyesters (23.24). 

The rigid main chain liquid crystalline polymers PBO, the molecular formula being... 

Typical functions of substituted poly acetylenes are based on their (i) high gas permeability and (ii) electronic and photonic properties. The former originates from the rigid main chain and bulky substituents. Though electrical insulators, substituted polyacetylenes are more or less conjugated polymers, and this feature has been utilized to develop their electronic and photonic functions such as photoconductivity, electrochromism, optical nonlinearity and ferromagnetism. 

Metal containing pol)miers with heterocyclic rigid main chains 07CCR2104. 

The first verification of the theoretical predictions of Onsager and of Flory that rod-like molecular chains might exhibit liquid-crystalline properties (see section 1.3.2 and chapter 12) was obtained in the 1960s and fibres from para-aramid polymers were commercialised under the name of Kevlar in 1970. These materials are very stiff and have excellent thermal stability many other materials of this class of rigid main-chain liquid-crystal polymers have been developed. They cannot, however, be processed by the more conventional processing techniques and this led to the development in the 1980s of another group of liquid-crystal polymers, the thermoplastic co-polyesters. 

Sekkat Z, Kang C S, Aust EF, Wegner G, Knoll W. 1995a. Room temperature photo induced poling and thermal poling of a rigid main chain polymer with polar azo dyes in the side chain. Chem Mater 7(1) 142 147. 

Liquid crystals (LCs) are described as a fluid phase that flows like a liquid and is oriented in a crystalline manner. LCs are divided into two types thermotropic LCs, where the LC phase transition is dependent on temperature or lyotropic LCs, where the LC phase transition occurs as a function of solvent concentration. To introduce liquid crystallinity to conjugated polymers, LC moieties can be introduced to the polymer side chains for side chain-type liquid crystallinity. On the other hand, designing conjugated polymers with rigid main chain structures with flexible alkyl side chains for solubility enables main chain-type liquid crystallinity. 

Chemical Structures and Synthesis. A variety of chemical structural units are available for use in the design and synthesis of liquid crystalline pol3nners. Flexible main chain pol3nners are depicted below in schematic form along with examples of chemical subunits. Rigid main chain polymers lack the flexible segment D. 

ORIENTATION PROCESSES IN RIGID MAIN CHAIN POLYMERS... 

Rigid and semi-rigid main chain systems, historically the first synthetic PLCs studied, are treated with emphasis on structural, morphological, and mechanical properties. More recent flexible main chain systems are discussed, focusing mainly on structure-property relationships. 

Fig. 8 CPK models of (A) p-structural Ala and (B) a-helical Leu derived from PEPCON. The black atoms present carbonyl carbons. A linear and planar solute such as pentacene provides more effective interaction area with the carbonyl groups one-dimensionally-aligned on the rigid main chain than a disk-like solute such as coronene (A). On the other hand, the carbonyl groups of Leu are covered with their bulky residual groups (B).

---