Semirigid-chain polymers

Fig. 6. The effect of the variation of the flexibility parameter for a semirigid-chain polymer (at X = 100) on the composition of coexisting phases (according to...

Miller et al. have shown that the variation of/for semirigid-chain polymers does not change the general form of the diagram. However, with increasing of flexibility a narrow heterophase region is shifted toward higher concentrations and considerably broadened. 

Valenti et al. noted a transition to the mesophase under the effect of the applied external field for those semirigid-chain polymers which do not exhibit the liquid crystalline transition under normal conditions. A moderately concentrated solution of polyterephthalamide of p-aminobenzylhydrazide (X-500) in dimethyl sulphoxide does not exhibit the transition into the liquid crystalline state, which can be explained by a relatively low axial ratio for the macromolecules. The persistence length for this polymer is estimated being equal to 50 A. At the same time, according to the data from the literature, high-modulus fibres have been obtained from the solutions of this polymer, which can be connected only with the appearance of the liquid crystalline state in the process of fibre formation. The authors of believe that this... 

The general scheme of the transition of semirigid-chain polymers from the non-equilibriimi amorphous state to the liquid crystalline or crystalline state is given... 

The rapid growth of the number of publications concerning polymeric liquid crystals indicates that we should expect the appearance of new fundamental studies on the transition of rigid- and semirigid-chain polymers into this state. The range of moderately concentrated solutions for these polymers is studied sufficiently well, while the development of the methods of establishing the liquid. crystalline state in superconcentrated systems and in pure polymers with semirigid chains, as well as the analysis of kinetics of phase transitions, are the subject for further theoretical and experimental works. 

Thermal Behavior of Semirigid Chain Polymers Glass Transition Temperature versus Crystallinity 238... 

Semicrystalline Structure of Semirigid Chain Polymers and Its Evolution during Crystallization and ... 

Similarly to the didectric analysis, the modification of the a-rdaxation spectrum during crystallization of a semirigid chain polymer can also be monitored by dynamic mechanical thermal analysis (DMTA) In this case, due to a more restricted frequency... 

In analyzing the thermal behavior of semirigid chain polymers, it is instructive to correlate the glass transition temperature not only with crystallinity but also with annealing temperature. Figure 20 shows such plot of Tg versus together with depen-... 

Typical SAXS results corresponding to isothermal crystallization of a semirigid chain polymer (PEEK) are given in Figure 24. In the top panel of the figure, one can see the SAXS curves corresponding to different crystallization times at a... 

Figure 26 Schematic illustration of the two possible models of the lamellar stack of semirigid chain polymers. Left, stacks with thin crystals and thicker interlamellar amorphous regions. Right stacks with thicker crystals and thinner interlamellar amorphous regions. The ambiguity of the microstructural model Is due to the Babinet principle, which makes the scattering from the two structures indistinguishable.

Ivanov D. Exploring the melting of a semirigid-chain polymer with temperature-resolved small-angle X-ray scattering. Eur Phys JE 2004 13 363-378. 

Finally, the third group, which will be primarily considered in the present chapter, includes rigid- and semirigid-chain polymers of linear structure which exhibit the properties of liquid crystals due to the pronounced geometric asymmetry of the macromolecules. According to the theory of the liquid-crystalline state, these polymers, described in detail in Chapter 1, pass into an ordered state with a certain (critical) concentration of polymer in the solution. 

FORMATION OF THE LYOTROPIC AND THERMOTROPIC CHOLESTERIC MESOPHASE IN RIGID-CHAIN AND SEMIRIGID-CHAIN POLYMERS... 

All of this explains the difference in the character of the phase diagrams for the same cellulose ethers, which in some cases are close to the phase diagrams characteristic of solutions of rigid-chain polymers as a function of the type of solvent, while the type of phase diagrams is satisfactorily described by the theoretical relations for solutions of semirigid-chain polymers in other cases (cf. Chapter 1),... 

It has been shown that a semirigid-chain polymer, hydroxypropyl cellulose with M = 60,000, turns into a LC melt at 160-205 C, characterized by the presence of a creep limit, like other melts and solutions of LC polymers. However, the fibers formed from such a melt have weak molecular orientation and low strength [58]. 

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