Asymmetrie of macromolecules

There can be the following causes of a sharp asymmetry of macromolecules ... 

Film formation is a specific property of polymers that distinguishes them from low-molecular matter. This is a considerable length and asymmetry of macromolecules capable of forming a strong oriented permolecular structure during stretching of polymer bodies that lies at the base of this property [2]. So far, polymers are considered to utterly suit to a raw material for production of the films. 

It is seen, that as the molecular mass of the polymer increases, the boundary curve corresponding to the development of anisotropic LC phase in solutions is shifted to lower concentrations. This behavior agrees with the existing theoretical concepts (Flory, 1956). According to Flory, the critical concentration of a polymer, 92 / above which the LC order arises, is related to the asymmetry of macromolecules x (the length-to-diameter aspect... 

X - asymmetry of macromolecules, q) - ionization potential, AT - the difference of phase transition tempreratures under dynamic and static conditions, y - shear rate, AT -the difference in LC phase transition tempreratures in the presence and absence of magnetic field, t - times of relaxation, AH - enthalpy of activation for the nematic liquid crystal-cholesteric hquid crystal transition, 002. mass portion of polymer. 

The chemical nature of the rubber determines which bonds are the weakest and are therefore more likely to be ruptured during mastication by the statistical concentration of mechanical energy about such bonds. An increase in the degree of asymmetry, an increase in the stiffness and the packing density of macromolecules facilitate mechanical scission resonance stability will influence the... 

All factors related to the arrangement of the polymer chain in space are classified as tertiary structure. Parameters measurable directly (the radius of gyration RG, the end-to end distance h, the hydrodynamical radius RH, and the asymmetry in light scattering intensity) or indirectly (interaction parameters, the second virial coefficient A2) are related to the dimensions, such as size and shape of the polymer chain in a specific solvent under given conditions of temperature and pressure. For the exact determination of the coil size of macromolecules, it is necessary to ensure that measure-... 

The particular type of asymmetry of the carbon atoms present in macromolecules obtained from monomers of type (X) has been discussed by Natta and Farina (81). 

The shape of a conformation can be characterized by various manipulations of the principal moments. The asymmetry of any one of the conformations is characterized by the dimensionless ratios 1 > L lL > L /L2 > OJ34,35 Spherical symmetry requires L lL2 = Lh)l = 1. Averaging of the corresponding principal moments over all conformations permits discussion of the asymmetry of the population of conformations in terms of (L2)I(Li) and (L2)/(L2). Examples of these dimensionless ratios are presented in Table 1.2 for four types of macromolecules, unperturbed by long-range interactions. In none of the four cases do the conformations have spherical symmetry. 

Small differences in Mco values, measured in polarized and non-polarized light, as well as low scat-tering asymmetry values close for different fractions testify about low polydispersity of the fractions and coil like conformation of macromolecules, which is of... 

Phase diagram asymmetry can be evaluated by (i) the ratio of the biopolymer concentrations at a critical point, (ii) the angle made by the tie-lines with the concentration axis of one of the biopolymers and (iii) the length of the segment of a binodal curve between the critical point and the phase separation threshold. Association of macromolecules usually changes both their excluded volume and the affinity for the solvent water. This results in nonparallel tie-lines on the phase diagram. Normally, the tie-lines can be nonparallel since an increase in concentration of biopolymers is usually accompanied by their self-association. Equilibrium between the phases is not achievable when phase separation is accompanied by gelation. 

In spite of the considerable difference in experimental and theoretical results obtained by different authors for the dimensions of macromolecules of aromatic polyamides, these results indicate a sharp asymmetry of the macromolecules. It should be pointed out, for the sake of comparison, that for flexible chain polymers the Kuhn segment amounts to only 20-50 A. For example, for an aromatic polyamide which does not exhibit coaxial rotation of the bonds, poly(m-phenylene isophtalamide), the Kuhn segment is equal to 50 A, i.e. it is 10-15 times as small as that for its para-analog. 

If the particle con be assumed to be unhydrated, or if the degree of hydration can be estimated with certainty from other experimental techniques, equation (8.15) may be used to determine the asymmetry of the particle. Alternatively, if the macromolecule may be assumed to be symmetrical or its asymmetry is known from other techniques, then this equation may be used to estimate the extent of hydration of the macromolecule. 

Although both faces of a biomembrane are composed of the same general types of macromolecules, principally lipids and proteins, the two faces of the bllayer are not identical. What accounts for the asymmetry between the two faces ... 

The diffusion coefficients D of macromolecules in dilute solutions have values of 10 cm /s (Table 7-1). The diffusion coefficients of the proteins ribonuclease, hemoglobin, collagen, and myosin, as well as deoxyribonuclease, were measured in dilute aqueous salt solutions. They were transformed into pure water diffusion coefficients by assuming that any differences are caused by differing viscosities only, and not by changes in the asymmetry or solvation coefficients. The diffusion coefficients of macromolecules in the melt are much lower, being 10" -10 cm /s. 

Thus, concentration dependence of sedimentation velocity increases with the size and asymmetry of the macromolecule. 

CARRAWAY, 1975). The method has been most widely applied to the covalent labeling of free amino groups of plasma membrane constituents and therefore seems somewhat restrictive and nonspecific, Similarly, the iodination of proteins with 131i is not target specific but certainly it has yielded much insight about transverse asymmetry of membrane macromolecules. 

Asymmetry of molecular shape is a feature that is common to all substances that exhibit liquid crystalUnity. The smdy of Uquid crystals involving macromolecules is a major subject in itself. It has been discussed in several reviews (80-83) and books.(84-88) It is not the purpose here to discuss liquid crystals involving polymers in any detail. Rather, efforts will be directed to place the behavior of such highly asymmetric molecules, and the transitions that they undergo without any conformational change, in perspective in terms of polymer crystallization. Thus, the effort will be in outUning the theoretical basis for the behavior and highlighting the unique features that result. 

As an example of the use of equation (4.5) to determine the viscosity of suspensions, one can refer to e works of Mullins [94] and Feldman and Boiesan [95] on rubbers containing fillers which are chemically inactive like wood flour or chemically active like carbon black. When the filler introduced is chemically inactive (with any ) or chemically active (with < 0.10), the quadratic form of equation (4.5) with aj = 2.5 and X2 = 14.1 could be used to give a good estimate of the viscosity of the suspension. For higher concentrations of the chemically active filler (carbon black), particle interaction begins and the viscosity of the suspension increases markedly and equation (4.5) as such cannot then be used for an estimate. However, if particle interaction leads to agglomeration, then Mullins [94] and Feldman and Boiesan [95] recommend the use of aj = 0.67 , and 02 = 1.62 in equation (4.5), where a, is the index of asymmetry of the elastomer macromolecules. 

In Ref. [25], the asymmetrical periodic function is adduced, showing the dependence of shear stress x on shear strain (Fig. 4.2). As it has been shown before [19], asymmetry of this function and corresponding decrease of the energetic barrier height overcome by macromolecules segments in the elementary yielding act are due to the formation of fluctuation free volume voids during deformation (that is the specific feature of polymers [26]). The data in Fig. 4.2 indicate that in the initial part of periodic curve from zero up to the maximum dependence of x on displacement x can be simulated by a... 

Keith HD, Padden FJ, Lotz B, Wittmann JC. Asymmetries of habit in polyethylene crystals grown from the melt. Macromolecules 1989 22 2230-2238. 

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. 

The formula is derived from Stokes law for the friction of a sphere moving through a liquid of a viscosity rj. The friction coefficient f is then equal to Gm/r. Friction increases as the shape of the molecule deviates from that of the sphere this is taken into account by the ratio of frictions /// , which is greater than unity. This value is of particular importance in protein chemistry it permits predictions concerning the asymmetry, or the ratio of axes, of macromolecules. 

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