Effect of oxygen pressure on the thermal degradation of a methylphenylsilicone

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Abstract
The manner in which changes in air pressure affect the thermal and oxidative degradation of a methylphenylsilicone was investigated as a function of time. A closed, gas‐circulating system of 1500‐cc. volume, incorporating a magnetic balance for following loss of weight in the sample, was employed. Finely ground samples were heated at 400°C. for 7 hours with initial pressures of air ranging from 700 to 50 mg. Hg. Mass spectrometric and infrared analyses identified the gaseous and the volatile products. At all pressures, low molecular weight silicones represented a major portion of the weight loss. Final weight losses in air approximated 10%, and approached, at the lowest pressure (50 mm.), the 7% observed in argon. Water and benzene were evolved, the latter at a rate that decreased with decrease in pressure. Traces of phenol, formaldehyde, propane, and higher molecular weight hydrocarbons were also given off. The evolution of carbon dioxide, carbon monoxide, methane, and hydrogen and the consumption of oxygen were followed in detail. Changes in air pressure from 700 to 300 mm. did not alter appreciably the rates of product evolution, oxygen consumption, and of weight loss. At lower presures (300 to 50 mm.), however, the molar ratio of the total noncondensed gases generated to total oxygen consumed increased, indicating a possible change in reaction mechanism.

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