Chemical reactions melting and compound formation

Chemical reactions that cause either the formation or severance of intermolecular crosshnks will also affect the stability of ordered chain structures. The role of crosslinks will be discussed in detail in Chapter 7. For polypeptides and proteins this is of importance in view of the relative chemical ease with which intermolecular disulfide bonds can be controlled. 

The quantitative formulation of the coupling of the crystal-liquid transformation with a chemical reaction involves specifying the phases in which the reaction occurs and the modifications induced in the chemical potential of the repeating unit The reaction can be treated by the usual methods of chemical equilibrium, the results of which are then imposed on the conditions for phase equilibrium. The different possibilities must be individually treated following this procedure. 

As an example we consider a simple type of complexing reaction that is restricted to the liquid phase. Consider a polymer molecule P containing n substituents each capable of complexing in the amorphous phase with reactant C according to the scheme 

For experiments carried out at fixed polymer concentration the last term on the right in Eq. (3.50) represents the depression of the melting temperature, at the given composition, due to the chemical reaction. If the factor Kuc is small, then 

Tmivi) represents the melting temperature of the mixture, which is devoid of the reactant, at the composition V2 and Tia,i(v2) is that after complexing. 

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In the interest of conserving space in this handbook, a compact tabular presentation format has been adopted. Table 5.1.5.1 lists the chemical name, and its freon number (if applicable), molecular formula, molar weight and melting and boiling points. These data are available for virtually all substances in this group. Also shown in this table is the availability, expressed as a tick mark, of data on vapor pressure, solubility in water, octanol-water partition coefficient (Kqw) and the second order reaction rate constant with hydroxyl radicals. This rate constant is the critical determinant of persistence in the atmosphere. Tables 5.1.5.2 to Table 5.1.5.5 list the compounds and give the available property data with citations. 

Effects of Additives. Selected additives to molten nitrate systems offer possibilities of specific acid-base reactions or formation of specific complexes with the various chemical species. Acids and bases are conveniently denoted in oxyanionic molten salt systems by the Lux-Flood definition (18, 19). Acids are defined as compounds capable of removing oxide ions from the melt, while bases are defined as compounds capable of donating oxide ions to the melt. Examples of various acidic and basic species may be found in the general review articles (14, 15,... 

The knowledge of the structure of these electrolytes is needed for the understanding of the mechanism of the electrochemical processes. The interaction of the components and the chemical reactions taking place in the melt effect the ionic composition, determining the kind of the electroactive species. The suitable choice of the electrolyte composition may suppress the formation of volatile compounds which leads to undesirable exhalation and lowers the efficiency of the process. 

Phosphorus is believed to perform most of its flame retardant function in the condensed phase (including both the solid and liquid phases, because various degrees of melting are involved at fire temperatures). Phosphorus-containing compounds increase the amount of carbonaceous residue or char formed by one or both of two mechanisms redirection of the chemical reactions involved in decomposition in favor of reactions yielding carbon rather than carbon monoxide or carbon dioxide and formation of a surface layer of protective char. 

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