Change in Solubility

Abnormal behavior can occur in the reaction of an initially homogeneous system if there is a change in the physical nature of the system on reaction of the polymer. Partial reaction may yield a polymer that is no longer soluble in the reaction medium or that forms a highly viscous system. The solubility changes can be quite complex, as shown in the chlorination of polyethylene when carried out in solution using aliphatic or aromatic hydrocarbon solvents 

Enhanced reaction rates have also been observed in some instances of decreased polymer solubility with conversion when the precipitating polymer absorbs the small-molecule reactant. Adsorption results in an increased concentration of the reactant at the actual polymerization site (the polymer coils). Similar effects are observed if a catalyst is adsorbed onto the precipitating polymer [Beresniewicz, 1959]. 

The rate of epoxidation of cyclohexene with perbenzoic acid decreases with increasing solvent polarity. The epoxidation by poly(peracrylic acid) shows the opposite trend. A polar solvent causes the polar polymer to swell to a greater extent and the reaction rate is increased due to a higher local concentration of cyclohexene [Takagi, 1975]. 

High crosslink densities may severely depress polymer reactivity as a result of large decreases in swelling and diffusion rate within the polymer. Diffusion control in a polymer reaction can be detected by the inverse dependence of rate on polymer particle size (radius for spherical particle, thickness for film or sheet) [Imre et al., 1976 Sherrington, 1988]. 

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Cross-linking which may lead to hardening, brittleness and changes in solubility. 

Buprofezin and its metabolites, p-OH-buprofezin and BF12, are hydrophobic under neutral conditions. Having the organic base part in their chemical structure, these compounds form water-soluble salts under strongly acidic conditions. The change in solubilities of these compounds influences the cleanup procedure. Four different residue analytical methods have been developed to measure buprofezin and its metabolites in plants (rice, citrus and tomato cucumber, pepper, tomato, squash and eggplant), soil and water ... 

Figure 6.4 On the left is a phase diagram for carbon dioxide. Broken lines indicate isotherm crossing at either constant pressure or density. On the right is illustrated the change in solubility of naphthalene as a function of temperature and pressure.

Changes in solubility product are one means of experimentally determining a value of activity coefficient, because we can independently determine the concentrations (e.g. via a titration) and the values of all y will be one at zero ionic strength. 

Polymer chemistry and polymer radiation chemistry in particular are key elements of the electronics industry. Polymer materials that undergo radiation induced changes in solubility are used to define the individual elements of integrated circuits. As the demands placed on these materials increases due to increased circuit density and complexity, new materials and chemistry will be required. Many of the new chemistries that are being developed are described in this article. 

At first glance the relationship between fullerene solubility and fatty acids unsaturation may appear as a surprise. However, it should be noticed that the unsaturation level of vegetable oils correlates also with their refractive index (Martinenghi, 1963). Thus, following the approach of Sivaraman et al. (1994), it is possible to show the change in solubility as function of the polarizability parameter of the solvent defined as ... 

Photolysis of the carbon-iodine bond in iodo-perfluoroalkyl compounds has been employed to enable the formation of the corresponding pefluoroalkyl radical [37]. Different perfluorinated alkyl chains can thus be covalently bound to the CNT. Interestingly, the authors reported that no change in solubility of the nanotubes was noted after the perfluoro-alkylation. 

Polymeric material that, when irradiated, undergoes a marked change in solubility in a given solvent or is ablated. 

Figure 8.8. Change in solubility where a solubility transus is intersected by Tc (fiom Takeyama el al. I99S).

The solubility profiles obtained for a compound which aggregates have the different regions as described previously, but the mathematical functions describing the change in solubility with pH are much more complex. The additional equilibrium for a monoprotic weak base when the charged species is aggregating is ... 

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