Solubility of polymer

This allows the calculation of osmotic pressure by Eq. (7), where c is the mass concentration of the polymer of molecular weight M. 

Equating the derivative of the mixing free energy [Eq. (6)] with respect to allows 

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Diphenyl compound (i.e. linkage bet >een rings) Melting range of polymer (°C) Solubility of polymer in ordinary solvents... 

Steric Stabilization. Steric stabilization was a term first introduced by Heller to explain how adsorbed polyethylene oxide polymers increased the salt concentration required for flocculation of negatively charged aqueous suspensions.(6) Heller s systems were stabilized by both mechanisms, as are most commercial dispersions today, aqueous and non-aqueous. Much of the more recent literature on steric stabilizers has been preoccupied with solubility requirements, for the solubility of polymers is a delicate matter and very sensitive to temperature and solvent... 

The calculations in Figure 3 were made on the assumption that the Hamaker constants of the adsorbed dispersant films are the same as the liquid media. This is an excellent assumption for polymers, since this means that the solubility parameter (6 ) of the dispersant and of the medium must be about the same, which is the basic requirement for solubility of polymers. 

Solubility of polymers in tetramethyl ammonium hydroxide aqueous solution was measured by dipping the wafer on which the polymer solution was spin-coated, for 1 min. at 25°C. The prebake was carried out at 90°C for 5min. Sensitivity of resists was measured after the exposure with CA 800(Cobilt) or KrF excimer laser(0.9mJ/cm2/1 pulse). The polymer structure was determined by iH-NMR, 13C-NMR(FX90Q apparatus,JEOL) and 2 Si-NMR. The molecular weight distribution was determined with a Toyo Soda Model 801 gel permeation chromatograph at 40°C. The four columns were connected in series, each packed with G-2000H8x3 and G-400H8(Toyo Soda polystylene gel), respectively. 

Staudinger, the final speaker, presented a broad array of data on polymerization, hydrogenation, comparisons of viscosity, melting points, and solubility of polymers. He pointed out that in the conversion of polystyrene to hexahydropolystyrene, and polyindene into hexahydropolyindene, the products retained their high molecular weight properties. Again, he maintained this proved "the monomers are united by main valencies" (62). 

Cross-linking is important because this is a major mechanism for retaining shape, which, in turn, influences the physical properties, such as solubility, of polymers. There are three types of cross-linking present in synthetic and natural polymer. Two of the three types are physical... 

There have been many attempts to describe the process of mixing and solubility of polymer molecules in thermodynamic terms. By assuming that the sizes of polymer segments are similar to those of solvent molecules, Flory and Huggins derived an expression for the partial molar Gibbs free energy of dilution that included the dimensionless Flory Higgins interaction parameter X = ZAH/RT, where Z is the lattice coordination number. It is now... 

The solubility of polymers is determined by the interactions between macromolecules and the molecules of the solvent. But the prediction of the solubility of a macromolecule and hence the correlation to its chemical (and morphological) structure is much more complicated than for a low-molecular-weight compound. Nevertheless, some general rules do exist ... 

The solubility of polymers decreases slightly as the molecular weight increases. This difference is sufficient to permit the separation of high-mo-lecular-wcight fractions of polymers by the addition of small amounts of a poor solvent to a polymer solution. It is also sufficient to permit preferential extraction of low-molecular-weight fractions of polymers. When a solution of a polymer is cooled, the first fraction to precipitate is the highest-molecular-weight fraction. It is customary to separate a solution of a polydisperse polymer into about five fractions and then to separate each of these fractions into three subtractions. 

The rules governing the water solubility of polymers are similar to those governing the water solubility of smaller organic molecules except that the extent of polymer solubility and the range of polymeric structures are more limited. Selected commercially available water-soluble polymers are shown in Figure 16.1. 

The presence of highly electronegative atoms which can participate in hydrogen bonding is required for the solubility of polymers in water. Such groups include amines, imines, ethers, alcohols, sulfates, carboxylic acids and associated salts, and, to a lesser extent, thiols. The water solubility is also affected by pH and the formation of charged species. Thus the copolymer derived from vinylamine and vinyl sulfonate is not soluble in water, whereas the corresponding sodium salt of this copolymer is water-soluble. 

Polymers and Supercritical Fluids. Prior to the mid-1980s, little information was published regarding polymer processing with supercritical and near-critical fluids (1). In 1985, the solubilities of many polymers in near- and supercritical C02 were reported. These polymers were examined for their ability to increase viscosity in C02-enhanced oil recovery (24). Since then, a number of studies have examined solubilities of polymers in... 

Table 3.1. Factors Affecting Solubility of Polymers/Resins in SCCO2...

Suitable gases in the form of supercritical fluids represent clean solvents/ carriers, which neither leave residues nor impose an environmental load. A number of factors determine the solubility of polymers in supercritical carbon dioxides (SCCO2) and these are given in Table 3.1. 

Therefore, die polarity and solubility of polymer can be modified deliberately by varying the nature of the components. High aqueous solubilities of polyamides and polyurethane threaded with crown ethers or CD are intriguing, because this observation implies potential applications of the polyrotaxane concept in coatings, adhesives, and water-borne processing. The observation of the emulsification of... 

Because of the (chain-length dependent) restricted solubility of polymers in hydrocarbons, solution polymerization requires higher temperatures and / or higher pressures. Technologically, solution polymerization processes are similar to the high-pressure LDPE process, see chapter 3, and will not be discussed here. 

Further experimental data are needed to draw reasonable conclusions about the differences in stereoisomeric composition or in solubility of polymers from optically active and racemic monomers. 

The solubility of polymers is, for thermodynamic reasons, more restricted than the solubility of low-molecular compounds and, consequently, the choice of solvents is limited. Potential solvents for most synthetic polymers are of moderate polarity. Alcohols and liquids of similar polarity are precipitants for many synthetic polymers. The search for a mobile phase that enables RPC through solvophobic interactions between the polymer and the nonpolar stationary phase requires attempts to make the mobile phase an unfavorable environment for the solute. This easily conflicts with the narrow limits of solubility of the polymer under investigation. Solubility effects are known to occur even in low-molecular RPC 92 94), but in polymer RPC they even may govern retention. 

It is well known that the solubility of polymers depends on their molar mass. This effect can be utilized for the evaluation of molar-mass distributions. With copolymers, solubility is determined by composition and molar mass. Topciev et al. derived the equation ... 

For hydrophilic water-soluble polymers, hydration is the first step of dissolution in aqueous solutions, followed by dissolution of the hydrated phase. The latter step involves disentanglement of polymer molecules. In general, the dissolution kinetics follow Eq. (5.2), suggesting that the solubility of polymers and the viscosity of the hydrated phase are the major variables affecting the dissolution rate. Diffusion of dissolved drug molecules through the hydrated polymer layer also may contribute to the overall release kinetics. 

There already exists a substantial literature devoted to the estimation of various material properties with the help of additive structual increments (Reid et. al, 1987, Van Krevelen, 1990). The regular solution theory in combination with additive structural increments has a wide application for estimating the relative solubilities of organic substances in polymers and the solubility of polymers in various solvents (Barton, 1983) and will be described later in this chapter. When estimating partition coefficient values, one is quickly confronted with this method s application limits, particularly with polar and non-polar structures, for example the partitioning of substances between polyolefins and alcohol (Baner and Piringer, 1991). 

Evidently, the most important application of the solubility parameters to be discussed in this chapter is the prediction of the solubility of polymers in various solvents. A first requirement of mutual solubility is that the solubility parameter of the polymer <5P and that of the solvent <5S do not differ too much. This requirement, however, is not sufficient. There are combinations of polymer and solvent for which solvent for which rip <5S, but yet do... 

So attempts to correlate solvent cracking and solvent crazing with solvent properties lead to the same conclusion as was drawn in Chap. 7 for the solubility of polymers, viz. that besides the solubility parameter at least one other solvent property must be taken into account. The method proposed by Vincent and Raha is one of several possible two-dimensional correlation methods. 

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