Solvent polarity solubility parameters

The solvent should have high solubility for the solute being crystallized. The capacity of the solvent to solvate can be quantitatively assessed through its solubility parameter value. Under the like dissolves like paradigm, anon-polar solute is generally more soluble in a non-polar solvent. Hence a solvent with solubility parameter value close to that of the solute can be assumed to have high solubility for the solute. The following empirical equation can be used to estimate the solubility parameter... 

Hildebrand developed solubility parameters to predict the solubility of nonpolar polymers in nonpolar solvents. The solubility parameter is the square root of the CED. For polar solvents, special solvent-polymer interactions can be incorporated into the solubility parameter approach. 

In contrast to the increasing solpar values of aliphatic hydrocarbon solvents, the solubility parameters of polar solvents, such as alkyl halides,... 

When heated. PP dissolves in nonpolar solvents with solubility parameters in the range of 6.5 to 9.5 H, but it is resistant to polar solvents, such as ethanol. PP is more resistant to environmental stress cracking than polyethylene. 

A rough rule of thumb would then be that if a polymer has a solubility parameter of say, 9, it should dissolve in solvents with solubility parameters between 8 and 10. Keep in mind that such considerations, approximate as they are, only apply to those systems that interact through dispersion and weak polar forces. 

Recently, Bagley (4, 5) confirmed Hansen s approach by measuring directly the internal pressure of several solvents. The solubility parameters Bagley obtained corresponded closely to the sum of the dispersion and polar forces that Hansen proposed,... 

Polymers containing long alkyl side chains are likely to have good resistance to water and alcohol since the solubility parameters of the polymer and solvents are quite different. Conversely, polar polymers, such as polyacrylonitrile, are predicted to show good resistance to attack by aliphatic hydrocarbons. By the same token, the longer alkyl chain acrylics are expected to be more soluble in aliphatic solvents since solubility parameter of the former polymers is more nearly equal to that of aliphatic hydrocarbons. These and related predictions of this theory have been experimentally verified innumerable times by coating chemists and formulators. 

Solvent performance Solubility parameter Kauri butanol value Hildebrand solubility parameter Polarity... 

Solvents have solubility parameters which fall within the contours of the map. However, at a given Hildebrand solubility parameter and hydrogen bonding index, the higher the solvent fractional polarity, the lower... 

The minimum in fractal dimension is mainly due to the polar contribution of the solubility Hildebrand parameter. This can be proved by the reproducibility of the minimum when the polar solubility parameter of Hansen is used, while no correlation between fractal dimension and the dispersive or hydrogen bond Hansen parameters can be found [69]. Moreover a similar tendency, but oppositely now showing a maximum, can hold for the glass transition temperature of the resulting membrane [67], as shown in Figure 5.9 with a very similar extremal Hildebrand parameter. The maximum glass transition temperature, or minimum fractal dimension, appears at a solvent Hildebrand parameter that very finely estimates that of the polymer. 

Panayiotou s method is based on the so-called PSPs (partial solvation parameters) which he has recently developed and applied in numerous cases (polymer-polymer miscibility, polymer-solvent interactions, solubility parameters, pharmaceuticals, phase equih-biia, etc.) (see Panayiotou, 2012b,c,d, 2013). The PSPs bear similarities with the Hansen solubility parameters presented in Section 3.4.2 but there are four distinct contributions due to dispersion, polarity, acid and base contributions ea, trca, < Gb and, moreover, there are predictive methods for their estimation. 

Taken together, these solvent-solute interactions make up the solvent polarity, which is represented well by Hildebrand s solubility parameter (1950). 

When more than routine water resistance is required, a copolymer vinyl acetate emulsion can be used. The plasticizing comonomer in the polymer particles increases their intrinsic coalescing ability thus, they can coalesce more readily than homopolymer particles to a film that has a higher resistance to water. This resistance to water does not extend to the organic solvents, however, which are better resisted by homopolymer films. The soft copolymers have lower solubility parameters than homopolymers and are more readily attacked by solvents of low polarity, eg, hydrocarbons. 

When viscometric measurements of ECH homopolymer fractions were obtained in benzene, the nonperturbed dimensions and the steric hindrance parameter were calculated (24). Erom experimental data collected on polymer solubiUty in 39 solvents and intrinsic viscosity measurements in 19 solvents, Hansen (30) model parameters, 5 and 5 could be deterrnined (24). The notation 5 symbolizes the dispersion forces or nonpolar interactions 5 a representation of the sum of 8 (polar interactions) and 8 (hydrogen bonding interactions). The homopolymer is soluble in solvents that have solubility parameters 6 > 7.9, 6 > 5.5, and 0.2 < <5.0 (31). SolubiUty was also determined using a method (32) in which 8 represents the solubiUty parameter... 

Table 5.5 Solubility parameters and partial polarities (P) of some common solvents...

As already mentioned molecules cohere because of the presence of one or more of four types of forces, namely dispersion, dipole, induction and hydrogen bonding forces. In the case of aliphatic hydrocarbons the dispersion forces predominate. Many polymers and solvents, however, are said to be polar because they contain dipoles and these can enhance the total intermolecular attraction. It is generally considered that for solubility in such cases both the solubility parameter and the degree of polarity should match. This latter quality is usually expressed in terms of partial polarity which expresses the fraction of total forces due to the dipole bonds. Some figures for partial polarities of solvents are given in Table 5.5 but there is a serious lack of quantitative data on polymer partial polarities. At the present time a comparison of polarities has to be made on a commonsense rather than a quantitative approach. 

Strictly speaking Eq. (8-51) should be applied only to reacting systems whose molecular properties are consistent with the assumptions of regular solution theory. This essentially restricts the approach to the reactions of nonpolar species in nonpolar solvents. Even in these systems, which we recall do not exhibit a marked solvent dependence, correlations with tend to be poor. - pp Nevertheless, the solubility parameter and its partitioning into dispersion, polar, and H-bonding components provide some insight into solvent behavior that is different from the information given by other properties such as those in Tables 8-2 and 8-3. 

Where, 5 is defined as the solubility parameter of the solvent. So, 8p and 8h are the dispersion, polar, and H-bonding forces, respectively. A homogenous mixture of polar solvents can also be used as the continuous phase. In this case, the solubility parameter of the homogeneous mixture is calculated according to the following expression [89] ... 

Paine et al. [85] extensively studied the effect of solvent in the dispersion polymerization of styrene in the polar media. In their study, the dispersion polymerization of styrene was carried out by changing the dispersion medium. They used hydroxypropyl cellulose (HPC) as the stabilizer and its concentration was fixed to 1.5% within a series of -alcohols tried as the dispersion media. The particle size increased from only 2.0 /itm in methanol to about 8.3 /itm in pentanol, and then decreased back to 1 ixm in octadecanol. The particle size values plotted against the Hansen solubility parameters... 

---