Persistence length twisting

It is considered that, if ideal, optically active poly(alkyl(aryl)silane) homopolymer and copolymer systems could be obtained which had stiffer main-chain structures with longer persistence lengths, it should be possible to clarify the relationship between the gabs value and the chiral molar composition. The magnitude of the chirality of the polyisocyanates allowed precise correlations with the cooperativity models.18q In the theory of the cooperative helical order in polyisocyanates, the polymers are characterized by the chiral order parameter M, which is the fraction of the main chain twisting in one helical sense minus the fraction of the main chain twisting in the opposing sense. This order parameter is equal to the optical activity normalized by the value for an entirely one-handed helical polymer. The theory predicts... 

Numerous investigators have proposed theories for the temperature dependence of pitch. " However, none completely explain the experimental results obtained for the various cellulosic systems. Of those proposed, Osipov s approach, which is based on a molecular statistical theory,takes into account steric and chiral interactions in solution to predict the influence of temperature and solvent on the pitch and twist sense of cellulose deiivatives. Assuming the cellulosic chain adopts a twisted belt as opposed to a helix, and the persistence length, /, of the cellulose chains is much smaller than that of a rigid chain, the twisting power could be expressed by... 

Morriss-Andrews, A., Rottler, and Plotkin, S. S. (2010J. A systematically coarse-grained model for DNA and its predictions for persistence length, stacking, twist, and chirality. The journal of Chemical Physics 132, 3, p. 035105. 

All distances will be given in monomer units- The degree of polymerization is denoted by (. Three elastic constants can be used to measure the elastic energy of deformation of the chain stretch, bend and twist"l"l. In the following, we concentrate on molecules for which the bend elasticity (constant B) is dominant. This leads to the wormlike chain model3, with an end-to-end distance = q i (c /1 i—and q = B/kT, is here the persistence length-... 

Cho and Lim compared the effect of a variety of lateral substituents on the thermal behavior of peripherally octasubstituted, metal-free phthalocyanines and their copper complexes. Despite being an interesting study, the characterization of the mesophases was tentatively made by optical microscopy and thus some doubts concerning mesophase identification still persist. The results of this study are gathered in Table 8 along with some metal-free and copper complexes discussed above to allow comparison. The free base with a chiral chain exhibited a texture resembling that of the cholesteric phase, whereas that of the copper complex was not identified. Compounds substituted with chiral chains were room-temperature liquid crystals, whatever the length and number of asymmetric carbon atoms, and the columns described a helical twist. ... 

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