Solubility Parameters of Selected Polymers

Table 6.2. Hansen solubility parameters of selected polymers...

Determining the solubility parameters of crosslinked polymers uses method based on their maximum swelling in binary solvents of variable composition. The two components of the binary solvent are selected in such a manner that the solubihty parameter of a polymer occupies position intermediate between the parameters of the components. The method is based on the assumption that the maximum swelhng of the polymer occurs when the solubility parameters of mixture and polymer are equal. There should be a maximum on the plot of swelling ratio versus binary mixture composition. 

For completeness of the above discussion, a few examples of solubility parameters for selected polymers are given in Table 2.16. More extensive listings can be found in the source literature (Shinoda 1978 Van Krevelen 1976 Grulke 1989 ... 

Table 2.19 Hansen solubility parameters for selected polymers at 25 °C. All values are in (J/mL). For some polymers, more than one set of 5 values are provided (a, b, etc.), indicating variability in experiments/fittings or polymer structure effects (comonomer, M-, additives, etc.). A much more comprehensive collection of such values can be found in the relevant handbook (Hansen 2000)...

The solubility parameter of a new polymer may be determined by any of several means. If the polymer is cross-Unked, the solubility parameter may be determined by swelling experiments (7). The best solvent is defined for the purposes of the experiment as the one with the closest solubility parameter. This solvent also swells the polymer the most. Several solvents of varying solubility parameters are selected, and the cross-linked polymer is swelled to equilibrium in each of them. The swelling coefficient, Q, is plotted against the various solvent s solubility parameter, the maximum defining the solubility parameter of the polymer. The theoretical extent of swelling is predicted by the Flory-Rehner theory on the basis of the cross-link density and the attractive forces between the solvent and the polymer (see Section 9.12). 

The highest losses in mechanical properties of a polymer take place when the solubility parameters of a polymer and solvent match. The same statement can be made when the polarities of a solvent and a primary polymer bond match. A close match of the solubility parameters or polarities results in the incompatibility of the polymer and the solvent. To be clear, incompatible here means that the solvent attacks the polymer. Selection of a polymer for a given chemical environment must be made by evaluating the materials that have the largest solubility differences or polarity differences with the chemical environment. For example nylon 6/6 resists cleaning solvents such as carbon tetrachloride, and polystyrene and ethylene glycol are incompatible. Nylon 6/6 has polar amide bonds, while carbon tetrachloride is a non-polar solvent. In comparison, water is a polar liquid and is absorbed by nylon 6/6. Similarly polystyrene and ethylene glycol are both polar, and thus interact. 

Small values of X promote polymer solubility. Because (5 is a smrogate for Xi, it can be used in much the same way as the interaction parameter. Naturally, it suffers from the same drawbacks, as well as those resulting fi om the assumption embodied in Eq. (9.5.3). Values of the solubility parameter for selected polymer and nonpolar solvents are listed in Table 9.2. These may also be estimated using the method of group contributions [27]. For a mixture of solvents, the solubiUty parameter may be taken to be a weighted average of the solubility parameters of the constituents weighting is done with respect to the volume fraction of the components. 

Grater, H. Schuster, R. H. Cantow, H.-J., "Thermodynamics of Polymer Systems. 5. Sorption and Mixing Properties of Selected Solutes and Solubility Parameters of Atactic Poly(Styrene) by Gas Chromatography," Polym. Bull., 14, 379 (1985). 

Selectivity and productivity depend on sorption and diffusion. Sorption is dictated by thermodynamic properties, namely, the solubility parameter of the solute(s)/membrane material system. On the other hand, the size, shape, molecular weight of the solute, and the availability of inter/intra molecular free space of the polymer largely govern the second property, the diffusion coefficient. For an ideal membrane, both the sorption and diffusion processes should favor the chosen solute. If one step becomes unfavorable for a given solute the overall selectivity will be poor [28]. 

The solubililty parameters of the SMA copolymers selected for this study were calculated using the Small equation (31) or by titrating with more polar and less polar solvents. In this method, 1.0 0.02 g of polymer was dissolved in a known volume of toluene and a measured volume of methanol was added until a stable turbid system was produced. The procedure was repeated with n-heptane. The solubility parameter of the copolymer was then determined from the summation of the product of the volume of toluene and its solubility parameter and that of non-solvent and its solubility parameter. The average value of these titrations was used to obtain the upper and lower turbidity limits and the mean of these two values was used as the solubility parameter (32). 

For example, in the coating and rubber industries the solubility parameter concept has been used respectively, to select solvents or to study swelling of cured rubber by solvents. Bohn has extended the solubility parameter approach to polymer-solvent systems [Bohn, 1968], Solubil-... 

Solubility of Polymers [14.35]-[14.42]. Most polymers are readily soluble if their solubility parameters are comparable to those of the solvent in question. The upper limit for good solubility is a difference in the solubility parameters of 6 units (Table 4). The following selected systems are not, however, mutually soluble despite the small solubility parameter difference AS ... 

The main aim for FCC gasoline desulfurization is to remove thiophenic sulfur compounds. Membranes made from polar polymers with solubility parameter close to thiophenic sulfur are used for desulfurization of gasolines by PV It is evident that solubility parameter of primary sulfur components of gasolines, that is, thiophenic sulfur components, is 19-21 (J/cm )", while for other hydrocarbons, these values are 14-15 (J/cm )". This difference can be exploited for separation by PV. Solubility parameter values of most of the polymers used as membrane material lie in the range of 21-26 (J/cm )". Thus, membranes made from these polymers afford good selectivity for thiophenic sulfur. Apart from various homopolymers, chemically and physically modified polymers have also been used for per-vaporative desulfurization. Some of these modifications include using different types and amounts of cross-linkers, blending two polymers, and copolymerization. Composite and treated ionic membranes have also been tried for this separation. Polymer membranes tried for this separation include PDMS/PAN, PDMS/PEI, PDMS/PES, PDMS/ ceramic, polyetherimine (PI)/polyester, PEG/PES, and PU/PTEE. ... 

In still other methods of evaluation, the solvents are selected so that the solubility parameter of polymer occupies an inter-... 

The solubility parameters (including Hansen s parameters) for selected polymers and plasticizers can be found in Tables 6.2 and 6.3. A further discussion of the Hansen methods is included in Chapter 5. 

Buckley-Smith (2006) discussed the use of solubility parameters to select man-brane materials for PV of organic mixtures. His research showed that Hansen solubility parameters (HSP) are a good screening method for PV manbranes, especially where the molecules being separated are of comparable size. Polymers that have HSP close to the desired component and not to other components tend to have the best selectivity and flux characteristics. However, diffusion is an important factor and is not completely accounted for by HSP. 

In conclusion, the macromolecular properties of polymers and their interactions with cell surfaces result in a specific pharmacokinetic behaviour of polymers. The routes of parenteral administration are far from being equivalent, e.g. the intraperi-toneal application often used cannot substitute the intravenous administration. Molecular parameters of the polymer circulating in the coitral compartment are changed in time not necessarily by a direct biological modification of the polymer but as a consequence of a selective processing of different fractions. The intracellular accumulation in secondary lysosomes is the only proven mode of persistence of a soluble polymer in tissues. Variations in the chemical structure of the polymer may result in a different pattern of polymer distribution in the body as a consequence of a different rate of cellular accumulation. 

A special feature in this book is the inclusion of the Hansen solubility parameter theory that can be used to classify solvents in terms of their nonpolar, polar and hydrogen bonding characteristics. Use of the Hansen solubility parameter theory will allow the worker to systematically search for a solvent substitute or determine the solubility of a resin/polymer in a certain solvent or solvent blend. The files necessary to construct computer spreadsheets that can utilize the Hansen solubility parameter theory are included with this book. The useful spreadsheet files on a computer disk are included in a plastic pocket on the back inside cover of the book. These files can be used on an IBM-compatible computer with Lotus 123 (or Excel) software. These computer spreadsheets were developed in the Lotus 123. WKl file format. The data files can be used with the Lotus 123 Version 5.0 for Windows, the Microsoft Excel Version 5.0 for Windows or any earlier version of the spreadsheet software. The files can also be translated into the Macintosh Excel format if the correct version of Excel is available. The coating industry will find the information on solvent substitution using the Hansen solubility parameter theory of particular interest. The use of computer spreadsheets to compare the solubility envelope of the polymer with likely solvent candidates has been very helpful to the author in past work and others in the coating in selecting substitute solvents or solvent blends. The Hansen solubility parameter values for 166 resins and polymers and 289 solvents are listed. 

Selection of a suitable solvent or blend for an industrial process or for determination of a resin or polymer solubility characteristics can make use of the Hansen solubility parameter theory. The solvent selection rules are applied by calculating the solubility parameters of the solvent or solvent blend to be replaced and then selecting new solvents that have similar solubility parameters. The concept is that the total solubility parameter value can be represented as a dispersion (nonpolar) 6, a polar 6, and a hydrogen-bonding 6 component. The total solubility parameter can be mathematically expressed as the square root of the sum of the squares of the nonpolar, polar, and hydrogen-bonding components as shown in Equation 1.1. 

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