https://onlinelibrary.wiley.com/doi/pdf/10.1021/js9604117

A Theoretical Model of Erosion and Macromolecular Drug Release from Biodegrading Microspheres

The equation that describes fragmentation kinetics, such as that which occurs in cluster breakup and polymer chain degradation (depolymerisation), is solved for models where the rate of breakup depends upon the size of the object breaking up. The resulting dynamic scaling behaviour is investigated. Both discrete and continuous models are considered.

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The kinetics of cluster fragmentation and depolymerisation

A theory of depolymerization of long chain molecules is developed on a statistical basis. It is assumed that all bonds connecting monomeric elements in the system have the same probability of being broken regardless of their position in a given polymer and regardless of the size of the polymer in which they are found. Expressions are derived for the distribution of molecular sizes in the depolymerized system as a function of the initial chain length and the average number of bonds split per molecule. Also, relationships are established between the average molecular weight of the degraded product and the average number of bonds split per molecule. Experiments on the acetolytic degradation of cellulose acetate are briefly discussed.

Theory of Depolymerization of Long Chain Molecules

Publisher Summary This chapter discusses the reaction that predominates in the dilute solutions of both glycoside and acid at temperatures of 100° or below––that is, hydrolysis. The method used for kinetic measurements is indicated in the chapter. Rate constants are obtained for the acid-catalyzed hydrolysis of salicin, starch, maltose, lactose, methyl α- and β-D-glucopyranoside, methyl α- and β-D-galactopyranoside, sucrose, and raffinose. The acid-catalyzed hydrolysis of polysaccharides is also reviewed in the chapter. Many factors seem to influence the rate of hydrolysis, including the ring size, configuration, conformation, and polarity of the sugar and the size and polarity of the aglycon. The hypotheses for which there is the most support are indicated in the chapter.

Acid-catalyzed hydrolysis of glycosides.

In this paper we discuss the application of a number of techniques that are currently being developed for use in life assessment/condition monitoring of transformer insulation, and we illustrate possible applications with some recent data. These include: high performance liquid chromatography (HPLC) of the oil to measure the product concentrations; size exclusion chromatography (SEC) of the paper to measure changes in molecular weight distribution (related to the degree of polymerization, DP) and computer modeling of the degradation process to relate chemical degradation rates to changes in physical properties, such as tensile strength, which is of critical importance in assessing the probability of damage to the paper under fault conditions. We also revisit the use of DP measurement as a means of assessing insulation life and present results that illustrate problems that we have identified in obtaining consistent data. We describe a method, developed from the British and American standards, which enables us to obtain reproducible results with a known variance. The aims of this paper are to present a limited review of techniques that are relatively new to the transformer monitoring field, to provide some recent results from this laboratory to demonstrate their potential application, and to show the need for a range of new tools, if we are to improve our ability to assess the condition of transformers and the remanent life of their insulation.

H. Mark

Papers

Degradation of long chain molecules