A new method for using pyrolysis-g.c.-m.s. to study the oxidative degradation of polymers or oils

The technique of pyrolysis-g.c.-m.s, has been extended to study oxidative degradation by a method which can deal with all types of samples. The method depends on the fact that when a pyrolysis filament unit is loaded into the pyrolysis chamber at the head of a g.c. column, it takes time (10 minutes or more) for the inert carrier gas to sweep away the air which has been admitted into the chamber during filament insertion. In normal thermal degradation work, the pyrolysis is not performed until all the air has been swept away. However, when it is desired to study oxidation, the pyrolysis may be performed whilst the air remains within the pyrolysis chamber, and during this time the concentration of air continuously monitored by the mass spectrometer. The use of this approach is illustrated by a study of the oxidation of a polyisobutylene oil. The pyrogram of the latter obtained in the presence of air shows distinct oxidation products which are not present in the thermolysis chromatogram obtained under inert atmosphere conditions. The results are also compared with those previously published for an enclosed Curie-point filament (ECP) study of the oxidation of this polymer. It is concluded that this new method is preferable to the ECP method, in that the latter method is more susceptible to the effects of secondary reactions occurring during this two-stage process. (C) 1999 Elsevier Science Ltd. All rights reserved.