The thermal degradation of some polyelectrolytes

All naturally occurring polyelectrolytes are found in an aqueous environment and this feature directed most of the chemical research in this field towards an understanding of polyelectrolyte behaviour in aqueous solution. The very rapid and steady progress in the field of synthetic electrolyte applications in industry has naturally stimulated further interest in the problems of synthesis and thermal stability of this type of polymer. A brief definition of polyelectrolytes, their classification, and a discussion of tacticity and cation binding in these materials is presented in Chapter 1. The introductory chapter also reviews briefly the relationships between the chemical structure and thermal stability of vinyl polymers. Chapter 2 summarises the apparatus and experimental techniques employed in the present study. The first part deals with the thermal analysis techniques and the second section describes the techniques used to identify the degradation products both qualitatively and quantitatively. Monomer preparation, polymerization, and characterization of monomers and polymers is considered in detail in Chapter 3. A brief account of thermal stability of monomers is also included in this chapter. The thermal degradation of alkali metal salts of polymethacrylic acid is discussed in detail in Chapter 4. The decomposition of these homopolymers is shown to involve depolymerization accompanied by the formation of metal carbonate and cyclic ketones. A mechanism of thermal degradation of the salts of polymethacrylic acid is postulated based on the results obtained. Chapter 5 details the thermal decomposition of divalent metal salts of polymethacrylic acid, which provides further support for the mechanism proposed in Chapter 4. In Chapter 6 studies of the thermal degradation of zinc polymethacrylate are reported. The nature of the volatile products and structural changes which can occur during decomposition suggest a similar pattern of degradation to other salts. The maximum rate of volatilization of zinc polymethacrylate is shown to occur at lower temperature than those of other divalent metal salts. The thermal behaviour of ammonium polymethacrylate is examined in Chapter 7. Thermal decomposition is shown to result in a cyclization reaction between adjacent monomer units before fragmentation to volatile products. Comparisons are made between ammonium polymethacrylate, polymethacrylamide and polymethacrylic acid degradation, hence thermal decomposition of the latter homopolymers is also considered in Chapter 7