The investigation of the thermal degradation or pyrolysis of vinyl polymers has been pursued from the theoretical and the experimental standpoint for polystyrene,' polymethyl methacrylate,2 and polythene.3 The degradation of the first two polymers seems to be predominantly a depolymerization, while that of polythene is a process of random chain scission. The methods have been weight loss, viscosity studies, molecular weight distribution, osmotic measurements, and infrared analysis. The oxidative degradation of vinyl polymers has been extensively studied by Tobolsky,' who emphasizes that a combination of analytical methods is necessary for a complete analysis of such a complex process.This paper presents the oxidative degradation of polyvinyl formal at high temperatures, studied by the infrared method in conjunction with weight loss, color development, and chemical analysis. Polyvinyl formal, like many other materials used in electrical insulation, undergoes severe changes in its physical, chemical, and electrical properties when exposed to high temperatures in the presence of air. It changes from a strawcolored resin of good Electrical properties to a deep brown embrittled material of high dielectric constant. Loss of solubility precludes such methods as viscosity measurements as methods of analysis during degradation. However, the infrared spectrum, because of its sensitivity to molecular structure and structural changes, has been valuable in detecting the changes in the polymer during degradation.. EXPERIMENTAL Materials. Commercial polyvinyl formal resin, or Formvar "E" obtained from Shawinigan Products Corporation, was analyzed by the manufacturers to contain 6% free hydroxyl groups, 12% acetate groups, 0.9% moisture, and 0.14% free hydroxyl acid. The hemi-formal content was believed to be insignificant; the molecular weight was approximate!y 22,000. Osmotic measurementst made in this laboratory on dioxane solutions of * The research described in this paper was carried out under sponsorship by the Office t
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