Rigid Chain Molecules

As already mentioned, the optical anisotropy of a rigid-chain molecule is its second main property determining the value and sign of birefringence observed in solution. It is characterized by the difference between the main optical polarizabilities 7i,... 

In principle, for kineticaEy rigid chain molecules, just as for ellipsoids, Eq. (62) is obtained as a consequence of Eq. (61) since in this case the value and orientation of flow birefringence are determined by the rotational mobility of a molecule as a whole. However, for an assembly of chains of similar masses but frozen in different conformations it is necessary to take into account the conformational distribution. 

In contrast, if rigid chain molecules are of a rod-like shape (for a worm-like model x— 0), there is no conformational polydispersity in the assembly and comparison of Eqs. (61) and (62) gives G = 0.5. This is close to the value of G for a kinetically rigid (Jaussian coil both for weak (G = 0.667) and strong (G = 0.504) hydrodynamic interactions. 

The possibility of using the Kerr effect for the study of the structure and conformation of polymer molecules greatly depends on whether it is used for solutions of flexible-chain or rigid-chain molecules ... 

Figure 6. Schematic of alignment of rigid chain molecules, and the role of the anisotropic phase, x is the relaxation time. See also Hermans (15).

Hydrodynamic properties. The basic hydrodynamic characteristics of a macromolecule are its translational and rotational friction, experimentally studied by methods of diffusion, sedimentation, and viscometry. The chain necklace model [11], which has been very satisfactorily confirmed by the experimental data, is widely used in the hydrodynamics of rigid-chain molecules. 

Expression (2.47) sets the value of fiee energy for the phantom rigid chain molecule in a thermodynamically equilibrium state. 

We realize that the rigid reinforcement in traditional composite materials acts at the macroscopic level. As suggested in Ref. 19, we will call such materials heterogeneous composites. Problems inherent to their use can be eliminated in at least two ways. Helminiak, Hwang and their colleagues developed materials which they called molecular composites (MCs) rigid chain molecules dispersed at the molecular level in flexible chain polymers. The other way is to use PLCs—in which, in most cases, each chain already contains rigid and flexible sequences connected by primary chemical bonds. 

Spiro polymers are also sometimes classified as ladder polymers, and molecules in which the ladder structure is interrupted by periodic single bonds are called semiladders. Consisting entirely of fused ring structures, ladder polymers possess very rigid chains with excellent thermal stability. 

Generation of chemical linkages between long-chain molecules can be compared to two straight chains joined together by links. The rigidity of the material increases with the number of links. The function of a monomer is to provide these links. 

Hence, the main aim of the technological process in obtaining fibres from flexible-chain polymers is to extend flexible-chain molecules and to fix their oriented state by subsequent crystallization. The filaments obtained by this method exhibit a fibrillar structure and high tenacity, because the structure of the filament is similar to that of fibres prepared from rigid-chain polymers (for a detailed thermodynamic treatment of orientation processes in polymer solutions and the thermokinetic analysis of jet-fibre transition in longitudinal solution flow see monograph3. ... 

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