Flexibility and Shape of Macromolecules
| Autor: | V. N. Tsvetkov |
|---|---|
| Rok vydání: | 1963 |
| Předmět: | |
| Zdroj: | Rubber Chemistry and Technology. 36:337-350 |
| ISSN: | 1943-4804 0035-9475 |
| DOI: | 10.5254/1.3539562 |
| Popis: | The main feature of high molecular weight substances is the great size, chain structure and flexibility of the molecules. Investigation of macromolecules flexibility must be regarded as one of the most important tasks in the investigation of the structure of polymers. In the present article we shall deal quite briefly with certain results achieved in this field, which seem to us to be of fundamental importance. The cause of the flexibility of polymeric chains is the existence of a certain freedom of rotation around the valency bonds of the atoms making up the molecule. Nevertheless, this rotation is always more or less hindered by forces which may be either intramolecular (between the atoms of one and the same chain), or else inter-molecular (between atoms of a given chain and their molecules of the surrounding medium). It is possible to a certain extent to separate the influence of these forces from each other, by studying and comparing the properties of macromolecules in solutions (using different solvents) and in the solid phase. Here, nevertheless, we must keep in mind the difference between thermodynamic (equilibrium) and kinetic (nonequilibrium) flexibility of the polymer chain. The deduction of equilibrium flexibility is made on the basis of investigation of configurations (the dimensions and geometrical shape) of macromolecules in solution in the statistically equilibrium state; and of the kinetic, on the basis of investagation of the rate of the processes which convert the macromolecules from one equilibrium configuration to another. The vast majority of experimental work dealing with the determination of kinetic flexibility has been carried out for polymers in bulk (mechanical and dielectric relaxation processes). In this case the influence of the intermolecular reactions is just as great as that of the intramolecular forces, and therefore it is very difficult to separate these two effects. Therefore at the present time we have at our disposal for the determination of equilibrium flexibility of polymer chains considerably more experimental and theoretical possibilities than is the case for kinetic flexibility. |
| Databáze: | OpenAIRE |
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