Chain kinetic units

In the present context the word termination is applied not to the breaking-off of a physical chain, i.e., the cessation of growth of a particular molecule, but to the complete destruction of a kinetic unit, which means the irreversible annihilation of one ion pair. This kinetic termination, which is a well-understood feature of radical polymerizations, is a comparatively rare event in cationic polymerizations it may occur in several different ways and in some systems not at all. 

The mutual termination of growing chains which prevails in radical polymerizations must be ruled out for all ionic systems in which the opposite ions form separate kinetic units because of the electrostatic repulsion between like ions. However, in solvents of low DC in which the growing end of the polymer chain consists of an ion pair, a mutual termination by interaction of two such ion pairs is at least conceivable. 

If one considers that the reptation process is dominant for linear chains, one has to imagine additional processes of diffusion for polymers with long branches. The experimental data suggest strongly, however, that the basic kinetic unit of the chain (whatever it is) is the same as for linear chains the Rouse-like A and B processes are still there, which are still strong imprints of the "tube". 

Just as the equilibrium conformational properties of macromolecules, the theory of which has been developed in well-known classical works by Kuhn, Flory, Volken-stein and others the kinetic properties of polymer chains can be determined by two main mechanisms of intramolecular mobility. First, it is the discrete rotational isomeric (rotameric) mechanism of mobility caused by the jump of small-chain segments (kinetic units) from certain energically stable allowed conformers into others is4-i6S) gg ond it is the continuous mechanism of motion deter-... 

The majority of existing theories can neither determine precisely the size and the microstructure of kinetic units in a polymer chain of a given chemical structure nor rigorously predict the mechanisms and the kinetics of conformational transitions. In these theories, the properties of kinetic units are postulated and the aim of the theory is to study the effects resulting from the linking of these units into the chain. 

For all the models considered, the time dependence of the value 2(0 i characterized by a spectrum of relaxation times. The greater the relative thermodynamic chain rigidity (i.e. the greater the statistical correlation between the neighboring effectively rigid kinetic units), the broader is this spectrum ... 

These theories do not take into account a more isotropic distribution of centers of viscous resistance existing in an elementary kinetic unit (rigid segment) of the real chains. Often, the most bulky groups of monomer units are located on one side of the backbone chain. 

For the polyion equivalent conductivity, conditions are different. Here an appreciable concentration dependence is expected even in very dilute solutions. This is partly due to the direct dependence of Ap on a, a quantity that may vary with concentration, and partly due to the concentration dependence of the friction coefficient/p. As in the case of polymeric solutes in general, the friction coefficient depends on the polyion chain conformation, which for flexible polyelectrolytes is strongly concentration dependent. Furthermore, the polyion friction coefficient also includes contributions from the fraction (1 — a) of the counterions, which form a kinetic unit with the polyion. The friction coefficient can therefore be written in the form... 

The accelerated depolarization seen in Figure 1 reflects the presence of smaller rotational kinetic units in the polypeptide chain and not the ro-... 

The differences in dye-polypeptide interaction may explain the difference in measurements of the rotational relaxation time of poly Glu63Lys37 (No. 3) with the DNS and the fluorescein conjugates. The loosely bound DNS may less accurately reflect the true behavior of the rotational kinetic unit of the polypeptide chain in aqueous solution because it could interact with a portion of the chain remote from the point of attachment of the dye and give a spuriously long rotational relaxation time the tightly bound... 

Resistance to flow in polymer systems is greater than in low molar mass fluids, because now the molecules are covalently bonded into long chains, which are coiled and entangled, and translational motion must, of necessity, be a cooperative process. It would be unreasonable to expect easy cooperative motion along the entire polymer chain, but as there is normally some degree of flexibility in the chain, local segmental motion can take place more readily. The polymer can then be considered as a sraies of kinetic units each of these moves in an independent manner and involves the cooperative movement of a munber of consecutive chain atoms. 

Although it is thought that translation of a polymer ehain proeeeds by means of a series of segmental jumps involving short kinetic units, which may each consist of 15 to 30 chain atoms, the complete movement of a ehain eannot remain unalfeeted by the surrounding chains. As stated previously, eonsiderable entangjranrait exists in the melt, and any motion will be retarded by other ehains. 

Sols of long chain macromolecular colloids may be of the low viscous type if the kinetic units in their sols consist of densely built corpuscules — the long chain molecule being folded up — as is assumed to hold for many native proteins. 

If the kinetic unit is not built up in that way, the macromolecular colloids belong to the high viscous type, their long chain molecules forming statistical skeins in solution. 

One can hardly think of these kinetic units of the corpuscular proteins being stable otherwise than when lateral bonds (primary or secondary valencies) between groups of contiguous folds of the macromolecule or between subunits counteract to a sufficient extent the natural tendency of the long chain molecule to assume the most probable shape, that of the randomly kinked macromolecule. 

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