Polymer-Solvent Compatibility

Solvent-polymer compatibility problems are often encountered in industry, such as in the selection of gaskets or hoses for the transportation of solvents. A rough guide exists to aid the selection of solvents for a polymer, or to assess the extent of polymer-liquid interactions. A semi empirical approach has been developed by Hildebrand based on the principle of like dissolves like. The treatment involves relating the enthalpy of mixing to a solubility parameter, S, and its related quantity, 8, called the cohesive energy density. 

The second virial coefiicient A2, which is related to the Flory dilute solution parameters by Eq. (3.121), is a measure of solvent-polymer compatibility. Thus, a large positive value of A% indicates a good solvent for the polymer favoring expansion of its size, while a low value (sometimes even negative) shows that the solvent is relatively poor. The value of A2 will thus tell us whether or not the size of the polymer coil, which is dissolved in a particular solvent, will be perturbed or expanded over that of the unperturbed state, but the extent of this expansion is best estimated by calculating the expansion factor a. As defined by Eqs. (3.123) and (3.124), a represents the ratio of perturbed dimension of the polymer coil to its unperturbed dimension. 

Expansion Factor The second virial coefficient, A2, is a measure of solvent-polymer compatibility. Thus, a large positive value 0/A2 indicates a good solvent for the polymer favoring expansion of its size, while a law value (sometimes even negative) shows that the solvent is relatively poor. The value of A2 will thus fell... 

Harrington, MG Lee, KH Bailey, JE Hood, LE, Sponge-Like Electrophoresis Media Mechanically Strong Materials Compatible with Organic Solvents, Polymer Solutions and Two-Dimensional Electrophoresis, Electrophoresis 15, 187, 1994. 

As is evident from a consideration of Figs. 7-9, each of these chromophores has exhibited electro-optic activity exceeding that of lithium niobate while at the same time exhibiting auxiliary properties of chemical stability (Td >300 °C) and solubility that permits preparation of device quality materials [183,210-212]. These materials also illustrate another major direction in the preparation of electro-optic materials namely, the development of bridging segments that lead to improved chemical stability, improved solubility in spin-casting solvents, improved compatibility with polymer host materials, and which inhibit unwanted intermolecular electrostatic interactions (we shall discuss such interactions... 

Many investigators have opted to study polymer compatibility in solution in mutual solvents, because of uncertainty as to whether a bulk mixture is actually in an equilibrium stale. Compatible components form a single, transparent phase in mutual solution, while incompatible polymers exhibit phase separation if the solution is not extremely dilute. 

This report has been the only publication involving enzymatically-catalyzed free radical polymerization in supercritical C02, perhaps due to the difficulty in adequately matching monomer or polymer compatible systems with the solvent. 

Glues chosen for use in bonding material with low absorbency and permeability should not have high carrier (especially water) content. High-carrier glues require suflScient assembly time ( preferably open assembly) to allow for dissipation of most of their carrier. A better option would probably be to use solvent solutions of polymer compatible with the consolidant. 

The dissolution of a polymer in a penetrant involves two transport processes, namely penetration of the solvent into the polymer, followed by disentanglement of the macromolecular chains. When an uncrosslinked, amorphous, glassy polymer is in contact with a thermodynamically compatible liquid (solvent), the latter diffuses into the polymer. A gel-like layer is formed adjacent to the solvent-polymer interface due to plasticization of the polymer by the solvent. After an induction time, the polymer is dissolved. A schematic diagram of solvent diffusion and polymer dissolution is shown in Fig. 1. However, there also exist cases where a polymer cracks when placed in a solvent. 

The major disadvantages of solvent cementing are the possibility of the part s stress cracking and the possible hazards of using low vapor point solvents. Adhesive bonding is generally recommended when two dissimilar polymers are joined because of solvent and polymer compatibility problems. 

Dilution ratio, DR, is used to express the tolerance of solvents to diluents, most frequently, toluene. DR is the volume of a solvent added to a given solution that causes precipitation of the dissolved resin. This ratio can characterize the compatibility of a diluent with a resin solution in primary solvent. When compatibility is high, more diluent can be added. Only a multi-parameter approach provides a satisfactory correlation with solubility parameters. DR depends on the polymer concentration. With polymer concentration increasing, DR increases as well. T emperature influences DR in a similar manner. Determination of DR must be performed at standard conditions. DR can be related to the solubility parameters but such correlation depends on concentration. 

A.A. Tager [110] determined the change of AG ix by producing thermodynamic cycles using static sorption of solvent vapors on the polymeric specimens. However, in solution the polymer compatibility is influenced by the difference of the thermodynamic interaction parameters of the common solvent with each indvidual polymer. Additionally, compatibility in solution does not always correspond to that in the solid state (without a solvent). These shortcomings limit the appUcabihty of the AG ,jx estimation method that Tager developed. 

To aid dispersion of the carbon fiber in the polymer matrix, it is usual to apply a polymer compatible size, normally a lower molecular weight version of the polymer can be used, preferably in a water base (e.g. a polyurethane). If the fiber has an epoxy size, this must be removed by solvent extraction in a solvent degreasing plant. Under some conditions, it is possible to blend 10% epoxy sized fiber. If the thermoplastic polymer is to be used at high temperatures (e.g. PEEK), then the size must be temperature resistant, such as a polyimide. 

In order to ensure good compatibility between POSS and the matrix, one must match the polarity or solubility parameter of the POSS and the solvent, polymer or coating in which it is to be dissolved. POSS polarities span the whole gamut from extremely hydrophobic fluoroalkyl POSS used to make ultrahydrophobic surfaces [12], through progressively more polar variants such as alkyl POSS (low polarity), phenyl POSS (medium polarity), and water soluble types including PEG POSS, POSS trisulfonic adds, and octaammonium POSS. 

Quaternary pyridinium-type PAF composites with AgCl have been introduced as antimicrobials to kill bacteria efficiently. PAF-50 with AgCl loaded in the pore displays excellent antibacterial properties, even better than commonly used antibacterial materials. Formation of a dispersion with various solvents and compatibility with a large number of polymers, such PAFs can lead to large scale industrial production for different medicinal applications. 

All the polymer supports described so far for solid-phase chemistry have a common factor the main presence of a polystyrene backbone. Although this polymer matrix has good characteristics, such as chemical and mechanical stability (depending on the type and amount of cross-linker) and favorable loadings in solvent, its compatibility with polar solvents and large biomolecules, such as enzymes and receptors, is quite poor (121). In order to resolve these problems, several authors have replaced hydrophobic polystyrene with a more amphiphilic backbone. In the... 

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