Investigations of the chemical conversions of polycarbonates

Abstract

Polycarbonates, in particular poly‐4,4′‐bis(hydroxyphenyl)‐2,2‐propane carbonate, are distinguished by their thermal stability and may be processed at temperatures about 300°. The present report deals with some chemical conversions of this polymer, taking place in solution and in the molten state. In the fractional precipitation of the polymer from chloroform solutions by methyl alcohol an enhanced yield in the low molecular fraction is observed, the latter continually forming even on repeated precipitation. If a small amount of methanol, insufficient to precipitate the polymer, is added to the chloroform solution, a gradual fall in viscosity (which does not occur in absence of the alcohol) is observed. The reaction is accelerated in the presence of hydrogen chloride. Such precipitants as acetone and petroleum ether do not cause this effect. Alcoholysis is a characteristic reaction of the polycarbonates, taking place at a relatively high rate. An alcoholic solution of alkali will decompose the polycarbonate at room temperature and especially rapidly (within a few minutes) on boiling. In this way one may obtain with high yield bisphenol used for the synthesis of the polymer. The melting of polydisperse polycarbonates (ca. 300°) in the absence of atmospheric oxygen leads to a very rapid (10–60 min.) levelling of the molecular chain lengths and hence to decrease in polydispersity (according to fractional precipitation data), causing a corresponding fall in the viscometrically determined molecular weights. Such levelling annuls the harmful effect of the low molecular fractions on the properties of the material. At higher temperatures (350°) decarboxylation (evolution of CO2) is quite marked, and the formation of a certain amount of three‐dimensional polymer may be observed. Polycarbonates prepared by the heterophase polycondensation of phosgene with phenolates, for instance, 4,4′‐bis(hydroxyphenyl)‐2,3‐propane and containing hydroxyl and acyl chloride endgroups are capable of undergoing further polycondensation on heating to 270–300°C. for 30–60 min. or more. Hydrogen chloride is evolved. As a result the mean viscometric molecular weight may increase three‐ to fourfold in comparison with the initial compound. Additional polycondensation in the melt may also proceed by another pathway, without hydrogen chloride evolution but as the result of the elimination of a certain amount of 4,4′‐bis(oxyphenyl)‐2,2‐propane on endgroup interaction. This reaction is catalyzed by small quantities of titanium alcoholates. The high lability of the ester links in polycarbonates may also be illustrated on the example of the interaction between these polymers and other esters, in particular with polybis(phenyl)‐2,2‐propane terephthalate [OC6H4C(CH3)2C6H4OCOC6H4COO]. The reaction taking place without catalyst at temperatures above 300° results in a mixed polyster carbonate with composite properties.

Stability of high‐temperature polymers

“…These polymers were insoluble in all common solvents except sulfuric acid. The effect of introducing a sulfone group between the benzoxazole rings (I, a-c) on the thermoxidative stability of several aromatic polybenzoxazoles is shown in Figure 44 (Yakubovich et al, 1967a). These data indicate that introduction of the sulfone group had a small adverse effect on thermoxidative stability.…”