The thermal degradation of polyoxymethylene

The thermal degradation of polyoxymethylene has been studied in the dynamic molecular still. The energy of activation for the degradation of hydroxyl group terminated polymer increases from 5–7 kcal/mole in the early stages to 50–52 kcal/mole from about 40% volatilisation onwards. There is an inverse relationship between molecular weight and initial rate and this, together with the changes in molecular weight which occur during the course of the reaction and the fact that acetylation of the chain terminal hydroxyl groups inhibits the reaction, indicates a very close similarity between the overall reaction mechanism and that for the thermal degradation of poly(methyl methacrylate). From the shape of the rate curve obtained during the course of the reaction and the fact that the density of the residual polymer increases during the reaction it has been concluded that reaction occurs preferentially in the amorphous regions of the polymer. Molecular, free radical and ionic mechanisms have been considered in detail. An examination of minor reaction products and the effect of catalysts and inhibitors positively eliminates the possibility that a radical process is involved. In the presence of basic catalysts the reaction is undoubtedly anionic but the anionic and molecular mechanisms are virtually indistinguishable in the uncatalysed reaction although the molecular mechanism is preferred on energetic grounds.