Chain Scission in the Oxidation of Hevea. III. Effect of Temperature

Abstract

When molecular oxygen reacts with raw Hevea rubber in latex at 90° C, two molecules of carbon dioxide and two molecules of “volatile acid” (one molecule of acetic acid and one molecule of formic acid) are produced for each apparent scission of the hydrocarbon chain, estimated from changes of solution viscosity. This corresponds to the complete destruction of one isoprene unit, and if the several hydrocarbon end groups are oxidized, requires a minimum of six molecules of oxygen per scission. Estimates of oxygen requirements for scission during the accelerated oxidation of vulcanized Hevea rubber much lower than this have been made. It has been suggested that the apparent high efficiency of scission in vulcanized rubber is the result of the predominance of scission at crosslinks over random cutting of the hydrocarbon chain. To investigate the less likely possibility that the mechanism of the reactions which leads to scission changes sharply with the rate of oxidation, the earlier estimates of yields of scissions and of volatile acids during the oxidation of Hevea latex at 90° C have been supplemented by measurements at 70° C and at 110° C.