Cohesive energy density , polymer

Polymer gel Polymer cohesive energy density P (cal cm ) Deviation from geometric mean mixing rule parameter z Non-Gaussian elasticity parameter, N Curve fit crosslink density (10s mol cm-3) Experimental crosslink density (10s mol cm-3)... 

Cyclic bisphenol-A polycarbonate oligomers have been reported by Kambour et al. [1994] to be miscible with a broad range of polymers (cohesive energy density, CED = 300 - 500 MJ/m ) (much broader than linear PC). The cyclic oligo-... 

The solubility parameter is not calculated directly. It is calculated as the square root of the cohesive energy density. There are a number of group additivity techniques for computing cohesive energy. None of these techniques is best for all polymers. 

We shall devote a considerable portion of this chapter to discussing the thermodynamics of mixing according to the Flory-Huggins theory. Other important concepts we discuss in less detail include the cohesive energy density, the Flory-Krigbaum theory, and a brief look at charged polymers. 

Table 8.2 Values of the Cohesive Energy Density (CED) for Some Common Solvents and the Solubility Parameter 6 for These Solvents and Some Common Polymers...

The polarity of the polymer is important only ia mixtures having specific polar aprotic solvents. Many solvents of this general class solvate PVDC strongly enough to depress the melting temperature by more than 100°C. SolubiUty is normally correlated with cohesive energy densities or solubiUty parameters. For PVDC, a value of 20 0.6 (J/cm (10 0.3 (cal/cm ) has been estimated from solubiUty studies ia nonpolar solvents. The value... 

The permachor method is an empirical method for predicting the permeabiUties of oxygen, nitrogen, and carbon dioxide in polymers (29). In this method a numerical value is assigned to each constituent part of the polymer. An average number is derived for the polymer, and a simple equation converts the value into a permeabiUty. This method has been shown to be related to the cohesive energy density and the free volume of the polymer (2). The model has been modified to liquid permeation with some success. 

CRANK, J., and PARK, J, s., Dijfusion in Polymers, Academic Press, London and New York (1968) GARDON, J. L., Article enlilled Cohesive Energy Density in Encyclopaedia of Polymer Science and Technology, Vol. 3, p. 833, Interscience, New York (1969)... 

The polymer has a low cohesive energy density (the solubility parameter 5 is about 16.1 MPa ) and would be expected to be resistant to solvents of solubility parameter greater than 18.5 MPa. Because it is a crystalline material and does... 

Because of the high cohesive energy density and their crystalline state the polymers are soluble only in a few liquids of similar high solubility parameter and which are capable of specific interaction with the polymers. 

The flexibility and cohesive energy density or polarity of each group arc nearly independent of the other groups in the molecule to which they are attached (55 60).because of this, each group can be assigned an apparent Tg value, and the Tg value of a polymer becomes Che sum of the contri-... 

The mole fraction of the monomer units that are cross-linked in the polymer is X,., and nt is Ihe number-average number of atoms in the polymer backbone between cross-links. The temperature should be expressed in absolute degrees in this equation. The constant K is predicted to be between 1.0 and 1.2 it is a function of the ratio of segmental mobilities of cross-linked to uncross-linked polymer units and the relative cohesive energy densities of cross-linked and uncross-linked polymer (88). The theoretical equation is probably fairly good, but accurate tests of it are difficult because of the uncertainty in making the correction for the copolymer effect and because of errors in determining nf. 

The synthesis of block copolymers with blocks of ultralow cohesion energy densities on the basis of polystyrene-6-polybutadiene via two highly efficient polymer analogous reactions has been presented. 

The value of TMWV is dependent on the cohesive energy density (CED) of amorphous polymers, the extent of crystallinity in crystalline polymers, and the effect of reinforcements in polymeric composites. Thus, while a low molecular weight amorphous polymer may be satisfactory for use as a coating or adhesive, a chain length generally above 100 is often required if the polymer is to be used as an elastomer or plastic. 

Solvent-polymer compatibility problems are often encountered in industry, such as in the selection of gaskets or hoses for the transportation of solvents. A rough guide exists to aid the selection of solvents for a polymer, or to assess the extent of polymer-liquid interactions. A semi empirical approach has been developed by Hildebrand based on the principle of like dissolves like. The treatment involves relating the enthalpy of mixing to a solubility parameter, S, and its related quantity, 8, called the cohesive energy density. 

Secondary forces operate at longer distances (.25-50 nm) than covalent bonds. These secondary forces are much weaker than primary covalent bonds, but the forces are cumulative. Thus the cohesive energy of a polymer is equal to the summation of the cohesive energy density (CED) values for each mole of repeating unit ( < 2 kcal) in the chain. The CED of a liquid is defined as the energy of vaporization per unit volume, / E/V. 

Polymers decompose before they evaporate, so it appears that the concept of CED is not applicable to these materials. However, by finding a solvent with which a particular polymer mixes athermally, we can assign to the polymer by Equation (73) the same CED as that solvent. Thus cohesive energy densities for a number of polymers, as well as low molecular weight solvents, have been determined. Table 3.1 lists some representative examples of such data. 

Cohesive energy densities can be used on a limited basis to give quantitative meaning to the chemist s rule of thumb, like dissolves like. Specifically, the more alike a solvent and a polymer are in CED, the more nearly athermal their mixing will be. The more different the two are in this property, the more endothermic the mixing process will be. Remember that Equation (72) makes no provision for exothermic mixing. In the next section we see how such information might be used. Remember that Equation (71) is not limited to endothermic... 

TABLE 3.1 Values of the Square Root of the Cohesive Energy Density for Some Polymers and Low Molecular Weight Solvents... 

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