Polydimethylsiloxane thermal degradation

Thomas, T.H. and T.C. Kendrick, Thermal analysis of polydimethylsUoxanes. I. Thermal degradation in controlled atmospheres, J. Polym. Sci. A, 27 537 (1969). Blazsd, M., G. Garzo, and T. Szekely, Pyrolysis gas chromatographic studies on polydimethylsiloxanes and polyfdimethyl sUalkylene siloxanes), Chromatographia, 5 485 (1972). 

The chemical, physical, and thermal properties ana resistance to degradation of polysiloxanes is the result of the high energy (106 kcal/mol) and the relatively large amount of ionic character of the siloxane bond. The ionic character of the Si—O bond facilitates acid and base-catalyzed rearrangement and/or degradation reactions. Under inert conditions, highly purified polydiphenyl- and polydimethylsiloxanes are stable at 350 to 400 °C. 

Many industrial applications for polydimethylsiloxanes (PDMS) make use of their stability towards heat and radiation. However, under extreme conditions these macromolecules degrade and/or depolymerise and there is an ever present need for more thermally stable polymers and a better understanding of the degradation and depolymerization processes. The siloxane bond is the only bond involved in the depolymerization process whilst in the degradation process all bonds are involved. Indeed Hyde148 and... 

Epoxies modified with butadiene acrylonitrile copolymers with (32) amine or carboxy end groups have disadvantages. They are susceptible to thermal and oxidative degradation and also have poor hot/wet properties, i.e., they soften when exposed to heat and moisture for long periods. Polysiloxane rubbers such as polydimethylsiloxane have been considered as a possible alternative. 

Siloxanes exhibit high resistance to thermal and thermal-oxidative degradation. This property depends on the chemical composition and the number of carbonic groups in the molecule. Thus, for example, polydimethylsiloxane is resistant under strictly thermal load up to 200 °C, while polydiamylsiloxane, polydibutylsiloxane, and polydibenzylsiloxane are already degraded at this temperature [32]. 

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