Aliphatic hydrocarbons solubility parameters

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. 

The fluids have reasonably good chemical resistance but are attacked by concentrated mineral acids and alkalis. They are soluble in aliphatic, aromatic and chlorinated hydrocarbons, which is to be expected from the low solubility parameter of 14.9 MPa. They are insoluble in solvents of higher solubility parameter such as acetone, ethylene glycol and water. They are themselves very poor solvents. Some physical properties of the dimethylsilicone fluids are summarised in Table 29.2. 

Intermediate liquid 8 values are obtained by mixing liquids of known solubility parameter SPS makes use of this. The 8 value of the mixture is equal to the volume-weighted sum of the individual component liquid 8 values. Thus, the mass uptake of a miscible liquid mixture by an elastomer may be very much greater than the swelling which would occur in the presence of either one of the constituent liquids alone. The mixture could of course comprise more than two liquid components, and an analogous situation would apply MERL have applied this approach for the offshore oil-production industry to allow realistic hydrocarbon model oils to be developed,basically by mixing one simple aliphatic (paraffinic) hydrocarbon, one naphthenic, and one aromatic to proportions that meet two criteria, namely, that... 

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

Figure 8.2. Relation of solubility parameters (solpars or Hildebrand values) to boiling points and flash points, where A boiling points of aliphatic hydrocarbons B = flash points of aliphatic hydrocarbons C = boiling points of aromatic hydrocarbons D = flash points of aromatic hydrocarbons.

The principal polyolefins are low-density polyethylene (ldpe), high-density polyethylene (hope), linear low-density polyethylene (lldpe), polypropylene (PP), polyisobutylene (PIB), poly-1-butene (PB), copolymers of ethylene and propylene (EP), and proprietary copolymers of ethylene and alpha olefins. Since all these polymers are aliphatic hydrocarbons, the amorphous polymers are soluble in aliphatic hydrocarbon solvents with similar solubility parameters. Like other alkanes, they are resistant to attack by most ionic and most polar chemicals their usual reactions are limited to combustion, chemical oxidation, chlorination, nitration, and free-radical reactions. 

These highly amorphous elastomers have relatively low Tt values (—73 C) and tend to crystallize when stretched. The cold flow of these thermoplastic polymers is reduced when they are crosslinked (vulcanized) with a small amount (2%) of sulfur. Since these polymers of isoprene have a solubility parameter of 8.0 H, they are resistant to polar solvents but are soluble in many aliphatic and aromatic hydrocarbon solvents. The cross-linked derivatives swell but do not dissolve in these solvents. 

Branched substituents on the nucleus of PS impede the rotation but do not decrease the Tt to any great extent. The solubility parameter decreases as the size of the substituent alkyl groups increases. Thus although PS is not soluble in aliphatic hydrocarbon liquids, poly / cydohexylstyrene is soluble and serves as a viscosity index improver for lubricating oils. 

Mixtures of nonpolar solvents are normally characterized by the term solubility parameter (5). The difference in solubility parameters of mixture components provides a measure of solution nonideality.Mixtures of aliphatic hydrocarbons are nearly ideal, whereas mixtures of aliphatic hydrocarbon with aromatics show appreciable nonideality. Sometimes, it is difficult to predict the behavior of highly nonideal mixtures. Thermodynamic properties of binary and multicomponent mixtures have been dealt with extensively in the literature. " ... 

The CMC of the surfactant in the aqueous phase is changed very little by the presence of a second liquid phase in which the surfactant does not dissolve appreciably and which, in turn, either does not dissolve appreciably in the aqueous phase or is solubilized only in the inner core of the micelles (e.g., saturated aliphatic hydrocarbons). When the hydrocarbon is a short-chain unsaturated, or aromatic hydrocarbon, however, the value of the CMC is significantly less than that in air, with the more polar hydrocarbon causing a larger decrease (Rehfeld, 1967 Vijayendran, 1979 Murphy, 1988). This is presumably because some of this second liquid phase adsorbs in the outer portion of the surfactant micelle and acts as a class I material (Section C). On the other hand, the more polar ethyl acetate increases the CMC of sodium dodecyl sulfate slightly, presumably either because it has appreciable solubility in water and thus increases its solubility parameter, with consequent increase in the CMC of the surfactant, or because the surfactant has appreciable solubility in the ethyl acetate phase, thus decreasing its concentration in the aqueous phase with consequent increase in the CMC. 

The solubility parameter or cohesive force of an individual solvent is believed to result from its inner molecular forces of attraction. Individual molecular forces characterize and dominate certain molecular regions of the structure. For instance dispersion (or London) forces result from the association between the electron systems of two adjacent molecules and the arrangement of the electrons. These forces are not affected by temperature, they operate within a short distance, they are accumulative, and they are general They reside in all molecules and represent the total attractive force known in saturated aliphatic hydrocarbons. 

Solubility parameters are a measure of polarity that give a quantitative measurement to like dissolves like. They vary from 6 for nonpolar aliphatic hydrocarbons to 23.2 for water. This well-known parameter is adequately described in other publications (2,8). 

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. 

The corrosion resistance of SAN is similar to that of PS, but the cyano pendant groups can be hydrolyzed by hot acids or alkalis. SAN has a solubility parameter of about 10 H and is more resistant than PS to aliphatic hydrocarbon Mquids, such as those present In gasoline. 

The viscosity method for soluble polymers and the swelling method for cross-linked network polymers yield quite unambiguous values for polymer solubility parameters, so long as one is confined to a series of structurally similar solvents. For example, the data in Figure 6-1 apply to aliphatic hydrocarbons as well as to long-chain esters and ketones. Cycloaliphatic hydrocarbons and short-chain esters such as ethyl acetate deviate significantly from the curves shown. 

Figure 6-1. Influence of goodness of solvent, as measured by the solubility parameter, 6i, of the solvent, on the intrinsic viscosity. [17], of dissolved natural rubber and on the volume fraction, 02, of the cross-linked natural rubber polymer in aliphatic hydrocarbons, (O), long-chain esters, ( ), and long-chain ketones, (O). After data from G. M. Bristow and W. F. Watson. The solubility parameter is given in the traditional physical units.

Alternatively, if polymer particles are not quite soluble in aliphatic hydrocarbons, then they will tend to dissolve on the addition of aromatic hydrocarbons, or the more polar esters, ketones, ether-alcohols and alcohols. All of these solvents will increase either the solubility parameter of the paint solvent mixture, or its hydrogen bonding capacity, or both. If the particles dissolve, then thickening can only be carried out by polymer molecules. The effect of polar solvents on these has been described above. 

Simpler methods are also used. In the paint industry, Kauri butanol values are determined by establishing the tolerance of a standard solution of Kauri resin in n-butanol to the addition of diluents. This method is applicable to hydrocarbons (both aromatic and aliphatic) and CFCs. Figure 2.3.20 shows that there is a good correlation between the Kauri butanol number and the Hildebrand solubility parameter. The Kauri butanol number can be as high as 1000 (amyl ester of lactic acid) or 500 (Freon solvent M-162). 

Non-solvents have solubility parameters which are situated outside the boundaries of the solubility maps. Therefore, considering for example Figure 2.10, liquids such as the aliphatic hydrocarbons and alcohols have solubility parameters in this area and are therefore non-solvents for the Epikote resins. Aromatic hydrocarbons such as xylene, on the other hand, lie very close to the outer contour of the map but nonetheless outside it. Therefore, although they are not true solvents, they do have some partial solvent activity and are indeed compatible with the resins at high solids levels. 

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