Polymer mutual solubility

Solubility Parameter. CompatibiHty between hydrocarbon resins and other components in an appHcation can be estimated by the Hildebrand solubiHty parameter (2). In order for materials to be mutually soluble, the free energy of mixing must be negative (3). The solubiHty of a hydrocarbon resin with other polymers or components in a system can be approximated by the similarities in the solubiHty parameters of the resin and the other materials. Tme solubiHty parameters are only available for simple compounds and solvents. However, parameters for more complex materials can be approximated by relative solubiHty comparisons with substances of known solubiHty parameter. 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

Indeed, in the world of tomorrow we can expect new aspects of polymer solids to extend the conventional and successful structure ideas of this century. These, of course, were the recognition as molecular identities of the chains of repeating chemical monomers. The circumstances of those entities have resulted in interesting concepts of solubilities, viscosity, and other mechanics, and especially thermodynamic limitations m mutual solubility or comparability of polymer mixtures. But we have known for decades that even homogeneous regular chain polymers such as Carothers polyesters and polyamides formed solids with manifold imperfections and irregularities, such as order-disorder crystal configurations.(22,23)... 

According to Flory-Huggins theory, in the limit of x the critical x parameter is 0.5.(H) Below this value the polymer and solvent will be miscible in all proportions. Above this value, the solvent will not dissolve the polymer, but will act only as a swelling solvent. Thus, the pure solvent may not dissolve the polymer even though it is not crosslinked. If x is not , the critical value of x is larger, but the same qualitative arguments regarding mutual solubility of the solvent and polymer hold. Thus, the application of Equation 1 does not require that the pure solvent be able to completely dissolve the polymer, only that the solvent dissolve into the polymer by an amount that can be measured. 

Diffusion Theory. The diffusion theory of adhesion is mostly applied to polymers. It assumes mutual solubility of the adherend and adhesive to form an interphase. 

In contrast to some theoretical predictions (23, 46, 52) aggregation or phase separation in block copolymers occurs at a slightly higher total concentration than in polymer mixtures. Covalent bonding of the two kinds of blocks thus slightly increases the mutual solubility. Polystyrene blocks with M = 2000 dissolve in polybutadiene (Af = 75000) up to concentrations of about 20% (33). Therefore, special mechanical properties are, in general, only to be expected in sequence copolymers above a certain block length (in most cases M8 > 103). 

In emulsion polymerization the compartmentalization of reaction loci and the location of monomer in polymer particles favor the growth and slow down termination events. The contribution of solution polymerization in the continuous phase is strongly restricted due to the location of monomer in the monomer droplets and/or polymer particles. This gives rise to greatly different characteristics of polymer formation in latex particles from those in bulk or solution polymerization. In emulsion polymerization, where polymer and monomer are mutually soluble, the polymerization locus is the whole particle. If the monomer and polymer are partly mutually soluble, the particle/water interfacial region is the polymerization locus. 

A simple expression governs the solubility of a liquid solute in a solvent, provided the solvent is practically insoluble in the liquid solute and that, again, only dispersion forces are operative between them. The first condition yields for the activity of the solute in its practically neat liquid phase, as well as in the saturated solution in equilibrium with it, to a2 1 and In a2 0. This dispenses effectively with the first term on the right hand side of Eq. (2.10). For a given liquid solute, the solubility parameter of the solvent dictates the solubility and constitutes entirely the solvent effect on it. This fact has found much application in the determination of the solubilities of certain liquid polymers in various solvents, the mole fraction x2 and volume V2 then pertain to the monomer of the solute. If, however, the solvent is also soluble in the liquid solute, as is the case when a solvent is capable of swelling a polymer, then the mutual solubility is given by ... 

The mutual solubilities of components whose molecular sizes are drastically different is the case of the binary polymer-solvent systems, the molecules of the solute... 

Evidently, the most important application of the solubility parameters to be discussed in this chapter is the prediction of the solubility of polymers in various solvents. A first requirement of mutual solubility is that the solubility parameter of the polymer <5P and that of the solvent <5S do not differ too much. This requirement, however, is not sufficient. There are combinations of polymer and solvent for which solvent for which rip <5S, but yet do... 

Diffusion Theory. The diffusion theory of adhesion is mostly applied to polymers. It assumes mutual solubility of the adherend and adhesive to form a true interpliase. The solubility parameter, the square root of the cohesive energy density of a material, provides a measure of the intemiolecular interactions occurring witliin the material. Thermodynamically, solutions of two materials are most likely to occur when the solubility parameter of one material is equal to that of the other. Thus, the observation that "like dissolves like." In other words, the adhesion between two polymeric materials, one an adherend, the other an adhesive, is maximized when the solubility parameters of the two are matched ie, the best practical adhesion is obtained when there is mutual solubility between adhesive and adherend. The diffusion theory is not applicable to substantially dissimilar materials, such as polymers on metals, and is normally not applicable to adhesion between substantially dissimilar polymers. 

The mutual solubility of cellulose (CELLOHO CTA, PCT and PMMA in TFA-CH2CI2 offers the opportunity to determine if Flory s prediction applies to ternary systems consisting of cellulose or a cellulose derivative and a synthetic polymer. 

If the monomer and polymer are not mutually soluble, the bulk reaction mixture will be heterogeneous. The high pressure free radical process for the manufacture of low density polyethylene is an example of such reactions. This polyethylene is branched because of self-branching processes illustrated in reaction (6-89). Branches longer than methyls cannot fit into the polyethylene crystal lattice, and the solid polymer is therefore less crystalline and rigid than higher density (0.935-0.96 g cm ) species that are made by coordination polymerization (Section 9.5). 

Relative sorption of the permeants in the membrane depends on the interactions between the solutes and the membrane polymer. Solubility or miscibility of a component with the membrane polymer depends on their relative solubility parameter values. For mutual solubility of two components their free energy of mixing, AGm should be negative. 

For some applications, polymers are blended to provide a balance of properties. Some polymers blend well due to mutual solubility, but if the solubility parameter of the candidate polymers is different by more than about 3 SI units, the polymers must be blended with an intermediate material to improve compatibility. Typically, this involves an intermediate polymer with a low molecular weight. In the melt, this serves to reduce the surface tension between two incompatible polymers, thus improving dispersion. Low molecular weight polyethylene is an example of a polymer blending aid. In other cases, metal stearates or salts can be used to aid dispersion. Examples include zinc stearate and calcium stearate. 

Model II. Some monomers have high monomer-water mutual solubilities compared to styrene (Table I) (5). For the swelling of these systems, neglect of the effect of water dissolved in swollen particles as well as in the monomer phase could lead to significant errors. Therefore, free energy terms describing the water-monomer and water-polymer interactions should be included in the equilibrium equations to cover a wide range of monomers. 

Mutual solubility of two polymers is promoted when the solvent favors the polymer that is most difficult to dissolve. This is usually the one with the higher molecular weight. It is clear that selection of the optimum solvent for this process of designed generation of an interface is aided by systematic use of cohesion energy parameters. 

Like certain combinations of metallic elements which show degrees of mutual solubility, so organic polymer blocks show varying tendencies to "alloy" in the solid state. The synthesis and properties of block polymers is a developing science which leads to important materials and engineering applications.(65) In this section we describe the preparation of a BAB block terpolymer of f-methylstyrene and styrene.(66) Sodium atoms are used to initiate polymerization in liquid tetrahydrofuran solutions of monomer cooled... 

The binary mixture of (two) polymers is considered a compatible blend, when a homogeneous solid system is formed, without phase separations. It means a complete mutual solubility of the two polymers in molten state as well. This compatibility is reflected in — among other physical and mechanical properties, — the fact that the system will have one single glass transition temperature (Tg). This miscibility of the most important thermoplastics in binary systems is seen on Fig. 1 [8],... 

Mumal solubilities of liquids vary greatly at ambient temparature. water and ethyl alcohol are miscible in all proportions, water and benzene are only very slightly soluble in one another, while benzene and mercury show essentially no mumal solubility. For most liquid pairs, mutual solubility increases with rising temperature, but meny exceptions are kaown a few pairs are completely soluble in one another at low temperatures and at high tempeimares with limited miscibility in between, while others (notably polymer-solvent systems) show complete miscibility only between lower and upper temparature limits. 

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