The determination of the transformation products of epoxides used in the heat stabilization of poly(vinyl chloride)

Methyl 9, 10-epoxyoctadecanoate has been used as a model compound to study the mode of action of epoxides when employed in the stabilization of poly(vinyl chloride) (PVC). Sheets of PVC containing 2% radioactively labelled methyl (1-¹⁴C]) 9,10-epoxyoctadecanoate (both with and without calcium/zinc stearate) were prepared on a hydraulic press and subsequently heated in an oven for various times to simulate heat processing. The polymer was separated from the low molecular weight components by steric exclusion chromatography, the extent of bonding of epoxide to the polymer being monitored by the ¹⁴C] activity of the high molecular weight fraction, and the level of residual methyl 9,10-epoxyoctadecanoate being determined colorimetrically on the basis of the epoxide concentration. The main transformation product was identified by combined gas chromatography-mass spectrometry as the methyl 9,10-chlorohydroxyoctadecanoate which was subsequently quantified after suitable derivatization by electron capture gas chromatography. A direct correlation was shown between the loss of epoxide and the extent of heat processing but this loss could not be fully accounted for on the basis of the estimated levels of chlorohydrins.