Amorphous polymers Polymer-solvent interaction

The term random coil is often used to describe the unperturbed shape of the polymer chains in both dilute solutions and in the bulk amorphous state. In dilute solutions the random coil dimensions are present under Flory 0-solvent conditions, where the polymer-solvent interactions and the excluded volume terms just cancel each other. In the bulk amorphous state the mers are surrounded entirely by identical mers, and the sum of all the interactions is zero. Considering mer-mer contacts, the interaction between two distant mers on the same chain is the same as the interaction between two mers on different chains. The same is true for longer chain segments. 

Q are the absorbance and wavenumber, respectively, at the peak (center) of the band, p is the wavenumber, and y is the half width of the band at half height. Liquid band positions ate usually shifted slightly downward from vapor positions. Both band positions and widths of solute spectra are affected by solute—solvent interactions. Spectra of soHd-phase samples are similar to those of Hquids, but intermolecular interactions in soHds can be nonisotropic. In spectra of crystalline samples, vibrational bands tend to be sharper and may spHt in two, and new bands may also appear. If polarized infrared radiation is used, both crystalline samples and stressed amorphous samples (such as a stretched polymer film) show directional effects (28,29). 

Flory and Huggins developed an interaction parameter that may be used as a measure of the solvent power of solvents for amorphous polymers. Flory and Krigbaum introduced the idea of a theta temperature, which is the temperature at which an infinitely long polymer chain exists as a statistical coil in a solvent. 

In Chapter 6 we talked about the ability of solvent molecules to interact with and surround amorphous polymer chains, leading to the formation of polymer solutions. A closely related phenomenon utilizes a low-molar mass compound to penetrate a polymer and reduce the forces of attraction between chains. Such a compound is called a plasticizer. It must be compatible with the polymer and is almost always nonvolatile. Solvent molecules actually plasticize a polymer sample before forming a solution. However most solvents are not good permanent plasticizers because they diffuse to the surface and evaporate. 

Conformations of polymer chains in dilute solutions under theta conditions are essentially identical to the random coil conformations of chains in amorphous polymers [26], where the interactions of polymer chains with solvent molecules are replaced by interactions between polymer chains. The density and the refractive index in the amorphous limit of a polymer are therefore the appropriate values of pP and nP to use in calculating the specific refractive index increment via Equation 8.16. The correlation developed for V(298K) in Section 3.C was hence used to calculate pP, and the correlation developed in Section 8.C was used to calculate nP. 

Molecules in the dissolved, molten, amorphous, and glassy states of macromolecules exist as random coils. This is a result of the relative freedom of rotation associated with the chain bonds of most polymers and the myriad number of conformations that a polymer molecule can adopt. As a consequence of the random coil conformation, the volume of a polymer molecule in solution is many times that of its segments alone. The size of the dissolved polymer molecule depends quite strongly on the d ee of polymer-solvent contact. In a thermodynamically good solvent, a high degree of interaction exists between the polymer molecule and the solvent. Consequently, the molecular coils are relatively extended. On the other hand, in a poor solvent the coils are more contracted. Many properties of macromolecules are dictated by the random coil nature of the molecules. We now discuss briefly the conformational properties of polymer chains. 

Hence, the results adduced above have shown correctness of the structure simulation, formed from different solvents, for amorphous PASF as totality ofWS clusters. This model parameters are defined by polymer molecular characteristics and interactions polymer-solvent. These results give... 

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