Photodegradation of poly(neopentyl terephthalate)

In this paper we investigate the mechanism of photodegradation in simulated sun light (in a SUNTEST XXL+) of a polyester based on terephthalic units (poly(neopentyl terephthalate); PNT). The mechanisms of degradation were studied with MALDI-ToF MS, ATR-FTIR and SEC. The mechanisms of the photodegradation are found to be very similar to those of the analogue polyester based on isophtalic units (poly(neopentyl isophthalate), PNI); in both cases the same type of degradation products were formed. However, all results indicate that PNT is much less UV stable than PNI, typically by a factor 13. This was explained in a quantitative way from the larger overlap of the spectrum of absorbance of PNT with the emission spectrum of the light source, as compared to the overlap in the case of PNI. In fact, a calculation indicates that the rate of degradation of both PNT and PNI under widely varying conditions is uniquely proportional to the totally absorbed amount of "photo-reactive" photons per unit of time, for a range of four decades in rate. No wavelength dependency of quantum yield was noticeable. --------------------------------------------------------------------------------