Analysis of the products formed during the photodegradation of poly(2,6-dimethyl-1,4-phenylene oxide) by various GC and HPLC techniques. Consequences for the mechanism of photodegradation

Abstract

In order to improve our understanding of the reactions occurring during the photodegradation of poly(2,6-dimethyl-1,4-phenylene oxide) we analyzed the formed products which were eluted from the irradiated solid polymer material by three different chromatographic techniques, namely GC/MS, HPLC/MS and HPLC in combination with a diode array detector. We found that there are only a few types of chromophores, like xanthones, lactones and benzoquinones which are responsible for the yellowing. These coloured species and several types of colourless species each appear in a series of homologous compounds differing by one monomeric unit. In most cases it is only one monomeric unit which is modified, e.g. by oxidation of the methyl groups. In combination with the results obtained by time-resolved experiments (Schneider S, Richter F, Brem B, 1998, Polym Degrad and Stab 1998; 61:453) several new conclusions can be drawn with respect to the mechanism of photodegradation in this polymer. The by far, most important primary photochemical process is the cleavage of the hydroxyl end group of the polymer. Secondary reactions lead to the scission of a nearby ether bond thus giving rise to the formation of homologous series of photoproducts. Since a variation of the spectral composition of the photolysis light did not result in a different product distribution, we conclude that the most important primary photochemical reaction steps are independent of excitation wavelength.