Flexibility of polymer molecules

The estimated equation of state parameters seem to have some physical significance e.g., they seem to be proportional to the polymer molecular weight. Moreover, it seems that the estimated b values represent a measure of the flexibility of polymer molecules for many polymers and for different approaches, the parameter b is closely related to the van der Waals volume. Generally, the performance of these cubic equation of state in correlating volumetric (PVT) data, although it varies from model to model, is satifactory considering the simplicity of the approach. 

The thermal energy of the molecular environment provides the energy required to overcome the rotational energy barrier. Consequently, the shape (flexibility) of a polymer molecule is temperature dependent. At sufficiently high temperatures, the polymer chain constantly wiggles, assuming a myriad of random coil conformations. As we shall see later, the flexibility of polymer molecules, which is a function of substituents on the backbone, has a strong influence on polymer properties. 

It is particularly interesting to consider the influence of the substituents R and Rj in diphenylol alkanes of the type shown in Figure 20.12. Such variations will influence properties because they affect the flexibility of the molecule about the central C-atom, the spatial symmetry of the molecule and also the interchain attraction, the three principal factors determining the physical nature of a high polymer. 

The structure and dynamic properties of this interacting array of polymer molecules depend on polymer conformation and flexibility. This also applies to the magnitude of C, which can be calculated on the basis of various geometric packing arrangements of the characteristic domain of the molecules. 

Therefore, when dealing with polyelectrolytes, countless Mark-Houwink relationships must be established. This shows the increasing problems of simple molecular weight determinations on charged systems (for more details, see Kulicke. Horl (1985)). Thus, the molecular weight determination of polymer molecules or additives is an important fact in the drag reduction area. Molecules or particles which are effective have molecular weights above 105 g/mol (the polymer backbone chains should be linear, flexible, and unbranched). 

Portions of polymer molecules which are in crystalline regions have overall dimensions and space-filling characteristics that arc determined by the particular crystal habit which the macromoleculc adopts. Here, however, we are concerned with the sizes and shapes of flexible polymers in the amorphous (uncrystallized) condition. It will be seen that the computation of such quantities provides valuable insights into the molecular nature of rubber elasticity. 

The possibility of using the Kerr effect for the study of the structure and conformation of polymer molecules greatly depends on whether it is used for solutions of flexible-chain or rigid-chain molecules ... 

Hence, as far as solutions of flexible-chain polymers are concerned, at present the Kerr effect cannot be considered as an effective method for the study of conformational and structural characteristics of polymer molecules. 

Nevertheless, desorption can occur over fairly short time scales, e.g., 15 min. It has been shown, for instance by using radio-labeled molecules, that flexible large polymer molecules do exchange between bulk and interface. Another indication is that two molecules of about equal surface... 

The special structure of polymer molecules that distinguishes them from other species is their long, flexible chain structure. To describe this situation, let us first consider an isolated polymer chain and then extend the results to ensembles of chains, that is, to the bulk polymer. An isolated linear polymer chain is capable of assuming many different conformations. Because of... 

Molecular structure, chain flexibility, and molecular weight determine the DR effectiveness of high polymers. Polymer backbone structure and side groups as well as solvent-polymer interactions determine the flexibility of the molecule [Patterson et al., 1969] as well as the polymer electrostatic charge in aqueous systems. 

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