General Descriptions of Degradation

The term charring refers to the complete degradation of a polymer after which there is no longer any polymeric character to observe. Charring results from chain scission reactions that are left unchecked and is the typical process by which thermosets degrade. The resulting material is typically black and brittle. 

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Study of the action of ammonia upon carbohydrate acyl esters originated some eighty years ago and, since then, many aspects of this complex reaction have been investigated. The processes that take place in this reaction include migrations, degradations, transesterifications, and deacylations, and their simultaneous occurrence makes the interpretation of the whole scheme very difficult. The present article provides a general description of the facts and a discussion of the different variables that play a role in the yields of products formed and in the mechanisms involved. 

This discussion will be confined to a general description of the biosynthesis and degradation of the glycerophosphatides commonly found in animal tissues. Reference will be made to the glycerophosphatides of plants and bacteria for comparative purposes only. Even with these severe restrictions, it will be possible to refer to no more than a small selection of the many important papers that have appeared on the subject during the past few years. 

Soil micas exhibit a wide variety of compositional, structural, and morphological features. This is also reflected by the nomenclature used in soil mineralogy. Hydrous mica, micaceous clay, sericite, illite, and degraded illite are some of the terms used, partly synonymously for the general description of fine-grained micas in soils, and partly with special reference to particular deviations from the ideal mica structure. 

In practice, there is only one really satisfactory solution the kinetics of the transformation must be followed. The justification for this substantial increase in effort is the dividend resulting in the form of a description of the metabolic pathway including the synthesis of possibly inhibitory metabolites. An important dividend is that it may be possible to make generalizations on the degradation of other xenobiotics—structurally related or otherwise. 

Similarly, Aga (excerpt 13A) describes the types of columns that she will use to achieve enantiomeric separation (an essential feature of her proposed work), but she does not devote space to a description of GC/MS parameters (e.g., temperature program, carrier gas, flow rates). She describes the general approach that she will use to analyze soil samples in the soil degradation study but provides few details on how soil moisture will be controlled or how the soil samples will be extracted and analyzed (details we would expect to see in a journal article describing this work). 

A detailed description of bulk polymers as hosts for geminal radical pairs and their precursors is also beyond the scope of this chapter. For general sources of information about photochemical and photophysical processes in bulk polymers, we recommend the classic book by Guillet as well as the book edited by Winnik, the journal Polymer Degradation and Stability (incorporating the defunct journal. 

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