Mechanisms of thermal degradation of phenolic condensation polymers. I. Studies on the thermal stability of polycarbonate

Abstract

AbstractBisphenol‐A polycarbonate gradually degrades at temperatures above 310°C. as detected by differential thermal analysis. The first stage of degradation of the dry and purified resin is induced by oxygen. In connection with oxidation, zinc stearate causes a notable degradation. This compound may act partly as an oxidation catalyst. The initial site attacked by oxygen is presumably the isopropylidene linkage of the polymer. The second stage of degradation shows a characteristic endothermic peak between 340 and 380°C. This stage is chiefly associated with depolymerization since only a small amount of volatiles is detectable. Depolymerization can be caused by hydroperoxide cleavage, hydrolysis, alcoholysis and bisphenol cleavage. Bisphenol‐A can decompose in the presence of acid into phenol and isopropenylphenol. The latter compound is a color‐forming material. As temperature increases above 400°C., volatilization rate gradually increases. The last stage of degradation becomes uncontrollable above 500°C. At this stage, decarboxylation, dehydration, hydrolysis, hydrogen abstraction, ether cleavage, crosslinking as well as chain scission interact to yield aromatic hydrocarbons, phenolic compounds, and tar. The quantity of aromatic hydrocarbons is determined by the intensity of the thermal degradation.