Hildebrand solubility parameter hydrogen bonding

Hildebrand solubility parameter Hansen three-dimensional solubility parameter Hydrogen bonding in polymer blends Association model Combinatorial entropy Chemical and physical forces Equilibrium rate constant... 

The parameters a and p indicate the capacity of a solvent to donate or accept a hydrogen bond from a solute, i.e., the solvent s hydrogen bond acidity or basicity. % is intended to reflect van der Waals-type solute-solvent interactions (dipolar, dispersion, exchange-repulsion, etc.). Equation (43) was subsequently expanded to include a term representing the need to create a cavity for the solute (and thus to interrupt solvent-solvent interactions).188 For this purpose was used the Hildebrand solubility parameter, 5, which is defined as the square root of the solvent s energy of vaporization per unit volume.189 Thus Eq. (43) becomes,190... 

In this respect, the solvatochromic approach developed by Kamlet, Taft and coworkers38 which defines four parameters n. a, ji and <5 (with the addition of others when the need arose), to evaluate the different solvent effects, was highly successful in describing the solvent effects on the rates of reactions, as well as in NMR chemical shifts, IR, UV and fluorescence spectra, sol vent-water partition coefficients etc.38. In addition to the polarity/polarizability of the solvent, measured by the solvatochromic parameter ir, the aptitude to donate a hydrogen atom to form a hydrogen bond, measured by a, or its tendency to provide a pair of electrons to such a bond, /, and the cavity effect (or Hildebrand solubility parameter), S, are integrated in a multi-parametric equation to rationalize the solvent effects. 

The following components of solubility parameters for PPO have been obtained (177) Sd = 16.3 1, Sp = 4.7 0.5, 6h = 7.4 0.5, and So = 18.5 1.2 with units (J/mL)"/2. The determination was based on the use of three mixtures of solvents. For each mixture, the point of maximum interaction between the mixture and the polyol was obtained from the maximum value of the intrinsic viscosity. The parameter 8d measures dispersion 8p, polar bonding 5h, hydrogen bonding and 5q is the Hildebrand solubility parameter which is the radius vector of the other orthogonal solubility parameters. Water solubility of PPO has been determined using turbidimetric titration (178) (Table 7). 

The Hildebrand solubility parameters may be calculated using group contribution methods, wherein the overall solubility parameter is the sum of contributions from Van derV feals dispersion forces, Sd dipole-dipole interaction and hydrogen bonding. 

This polarity index measures the intermolecular attraction between a solute and a solvent, whereas the Hildebrand solubility parameter is defined for pure solvent. For example, ether is not very polar and has a Hildebrand value of 7.4—about the same as hexane, which has a value of 7.3. However, ether can accept protons in the form of hydrogen bonds to its nonbonding electron pairs, and consequently its polarity index is 2.8 compared to 0.1 for hexane. 

The value of kd was obtained from the determination of triplet lifetimes by measuring the decay of phosphorescence and found to be insensitive to changes in solvent polarity. The k2 values derived from Eqs. 10 and 11 were correlated with solvent parameters using the linear solvation energy relationship described by Abraham, Kamlet and Taft and co-workers [18] (Eq. 12), which relates rate constants (k) to four different solvation parameters (1) or the square of the Hildebrand solubility parameter (solvent cohesive energy density), (2) n or solvent dipolarity or polarizability, (3) a, or solvent hydrogen bond donor acidity (solvent electrophilic assistance), and (4) or solvent hydrogen bond acceptor basicity (solvent nucleophilic assistance). 

Appendix L Hildebrand Solubility Parameter and Hydrogen Bond Index... 

Alphabetical List of Solvents with Values of Hildebrand Solubility Parameter S and Hydrogen Bond Index (1—10) y... 

Table 3 lists the Hildebrand solubility parameter 8, the total solubility parameter do, and the multicomponent parameters for dispersion dj, polar dp, and hydrogen bonding d/, forces for a number of solvents. These data are taken from the compilation by Barton (1975). He has pointed out that the data become empirical when multicomponent parameters are used, and thus it is important to use a set of data that are self-consistent. Keller et al. (1971) and Karger et al. (1976) have further subdivided the hydrogen bonding parameter into the acid or proton donor ( ) parameter, and the base or proton acceptor (6/,) parameter. Values for these are listed for some of the compounds in Table 3 from data provided by Snyder (1978). These data are not from the same source as those compiled by Barton (1975) and included in Table 3, and hence the values given for d/, should not be compared directly with those for 8 and 8. ... 

In the above considerations, the hydrophobic portions of both the membrane polymer and the small molecules that enter the membrane are expected to interact in the hydrophobic microphases in the membrane. It therefore becomes useful to find a numerical measure of the miscibility of these hydrophobic portions of molecules. In the case of complete molecules, both small and polymeric, the solubility parameter concept has been useful in the past. This concept is related to the enthalpy change which occurs on mixing in regular solution theory as developed by Hildebrand and coworkers (10) and as used for polymer solution theory by Flory (11). The Hildebrand solubility parameter is a measure of the attraction between molecules of the same kind, including dispersion forces, polar forces, and hydrogen bonding... 

The above interaction parameters may be related to the Hildebrand solubility parameter [22] 8 (at the oil side of the interface) and the Hansen [23] nonpolar, hydrogen-bonding and polar contributions to 8 at the water side of the interface. The solubility parameter of any component is related to its heat of vapourisation AH by the expression. 

Because the dielectric constant, DK (e), is strongly influenced by both dipole moment and hydrogen bonding, this single, simple measurement also provides a predictor of compatibility (17). The classical plasticizers for PVC fall between DK = 4 and 10. A two-parameter system, then, using the Hildebrand solubility parameter... 

For the analysis of SN1 solvolyses, Abraham et al. (9) have proposed an equation (equation 3) based on sensitivities toward solvatochromatic properties. In equation 3, tr is a measure of solvent dipolarity-polarization, a is a measure of solvent hydrogen bond donor acidity, and P is a measure of solvent hydrogen bond acceptor basicity. More recently, a term governing cavity effects has been added, and this term is considered to represent an important contribution (10, 11). The cavity term can be directly related to the square of the Hildebrand solubility parameter (10-12). A similar analysis by Koppel and Palm (13, 14) involves terms governed by solvent polarity, solvent polarizability, electrophilic solvation ability, and nucleophilic solvation ability. Recently, a cavity term has also been added to this analysis (12). 

Kamlet-Taft polarity/polarizability, hydrogen-bond donor (HBD), and hydrogen-bond acceptor (HBA) solvatochromic parameters taken from [138,148] 57 and p for TMP were obtained respectively from the correlations AN = 1.04 -I- 15.4(tr - 0.088) -I- 32.6a [149] and DN (kj/ mol) = — 3.8 -I- 163.9)3 [151], where 5 in this case only is a correction factor (not the Hildebrand solubility parameter) equal to zero forTMP. 

Certain solvents stand out as being unusually effective, pyridine and ethylenediamine being the most noteworthy. They are not uniqne, however, and any solvent having a Hildebrand solubility parameter of 11 and the capacity to serve as an effective hydrogen bond acceptor will be a... 

The first of these systems using three solubility parameters was proposed by Crowley, Teague and Lowe [11]. They chose for their parameters the Hildebrand solubility parameter for describing the dispersion forces, the dipole moment of the molecule to represent polar forces and a hydrogen bonding parameter based upon spectroscopic measurements of Gordy [12]. 

Nelson, Hemwall and Edwards have proposed a three parameter system which shows some similarity with that of Crowley, Teague and Lowe. It also uses the Hildebrand solubility parameter and a fractional polarity as suggested by Gardon, together with a net hydrogen bond index. This latter parameter is an attempt to... 

In a later stage it appeared to be more convenient to plot the hydrogen bond index against the Hildebrand solubility parameter as demonstrated in Figure 2.10. In this way of presentation contours of the maximum permissible fractional polarity can be indicated, which gives a good, and in practice very satisfactory, presentation of the three-dimensional case. 

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 viscosity dependence on polymer molecular weight is demonstrated in Figure 2.21 whereas Figure 2.22 shows the effect of polymer/solvent interaction. In the latter, the viscosity of solutions of a thermoplastic rubber at constant concentration and temperature is given in various hydrocarbon(blend)s. In this example hydrogen bonding or polar effects play no or only a very limited role. It is clear that in this case the solution viscosity is very much influenced by the Hildebrand solubility parameter of the solvent in relation to that of the polymer (8.2-9.1). 

Regular solution theory assumes that specific interactions such as hydrogen bonding are absent, and therefore Hildebrand solubility parameters are generally applicable only to systems containing relatively nonpolar constiments. It is important to remember that neither of these approaches are theoretically justified for mixtures in which specific solvation interactions are important. 

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