Solubility complications inherent

These results point to the fact that the steric complications inherent of the heterogeneous solid-phase reactions occuring in cross-linked polymeric matrices are not solved completely by the use of the corresponding non-crosslinked soluble polymeric supports. The equivalence of all functional groups attached to the linear macromolecular chain, therefore, appears to be a prerequisite for the attainment of the reaction facility prevailing in low-molecular weight systems. 

A frequent complication in the use of an insoluble polymeric support lies in the on-bead characterization of intermediates. Although techniques such as MAS NMR, gel-phase NMR, and single bead IR have had a tremendous effect on the rapid characterization of solid-phase intermediates [27-30], the inherent heterogeneity of solid-phase systems precludes the use of many traditional analytical methods. Liquid-phase synthesis does not suffer from this drawback and permits product characterization on soluble polymer supports by routine analytical methods including UV/visible, IR, and NMR spectroscopies as well as high resolution mass spectrometry. Even traditional synthetic methods such as TLC may be used to monitor reactions without requiring preliminary cleavage from the polymer support [10, 18, 19]. Moreover, aliquots taken for characterization may be returned to the reaction flask upon recovery from these nondestructive... 

There are inherent complications in partition studies. The presence of at least three components implies many possibilities for interactions. More important is the effect of the mutual solubilities of the two solvent phases. No two solvents are perfectly immiscible, and hence the data always refer to the partition of one component between two binary liquids. The effect of the usually small amount of dissolved solvent can be large. For example, a useful test for distinguishing m/ramolecular and intermolecular H bonding is the determination of the dry and wet melting points. The small amount of water that dissolves in the liquid phase has a pronounced effect on the melting point of intermolecularly H bonded substances. See Section 5.3.4 and Table 5-1V for examples and discussion of this effect. 

Two factors complicate these simple representations. They are the effect of increasing distiUation temperature caused by the increasing concentration of substrate and impurities. The impurities, in particular, can dramatically increase the solubility of the substrate. They can also decrease the inherent growth rate by blocking or inhibiting surface incorporation on the growing crystals or by reducing the nucleation rate. These effects are represented as curve H-E in Fig. 8-2. As distillation proceeds, the solubility increases. In extreme cases, the crystals once formed could melt as the temperature increases. 

In the Phillips process, polyphenylene sulfide (PPS) is obtained from the polymerization mixture in the form of a fine white powder, which, after purification, is designated Ryton V PPS. Characterization of this polymer is complicated by its extreme insolubility in most solvents. At elevated temperatures, however, Ryton V PPS is soluble to a limited extent in some aromatic and chlorinated aromatic solvents and in certain heterocyclic compounds. The inherent viscosity, measured at 206°C in 1-chloronaphthalene, is generally 0.16, indicating only moderate molecular weight. The polymer is highly crystalline, as shown by x-ray diffraction studies (9). The crystalline melting point determined by differential thermal analysis is about 285°C. 

To calculate gas solubility in natural geochemical systems, basic thermodynamic properties such as the Henry s law constant and, in the case of weak electrolytes the dissociation constant, must be combined with a thermodynamic model of aqueous solution behavior. An analogous approach has been used to predict mineral solubilities in concentrated brines (1). Such systems are also relevant to the atmosphere where very concentrated solutions occur as micrometer sized aerosol particles and droplets, which contain very small amounts of water relative to the surrounding gas phase. The ambient relative humidity (RH) controls solute concentrations in the droplets, which will be very dilute near 1(X)% RH, but become supersaturated with respect to soluble constituents (such as NaCl) below about 75% RH. The chemistry of the aerosol is complicated by the non-ideality inherent in concentrated electrolyte solutions. 

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