Oxygen photo degradability

The formation of appreciable quantities (up to "oQ0% based on the initial additive concentration) of the grafted substituted hydroxylamine O W0PP as from reaction 7) in photo-degrading PPH can be demonstrated by indirect methods (10, 11). For example after the rapid loss of the initial concentration of a piperidine or its nitroxide in PPH film, heating the film immersed in isooctane for several hours at 100 C in the presence of oxygen causes the re-appearance of nitroxide in appreciable quantities as measured by e.s.r. spectroscopy (ll). This nitroxide most likely results from a reaction analogous to reaction 8 (l2). In addition we have observed the ) N-0-C band (at 1306 cm 1) in the infrared spectrum of irradiated, nitroxide-containing PP films by Fourier Transform IR spectroscopy (ll)., ... 

In the end of this section the authors should like to add one thing that this photoreaction of the mechano-radical is considered a fundamental research of photo-degradation of a polymeric material in practical uses. A polymer suffers eaaly and very often from mechanical damages, sudi as scratch, during a practiral use. A mechanical scratch may produce mechano-radicals, and the reaction of the mediano-radicals with oxygens forms the peroxy-radkals, from which the chain sessions are induced by l t with high efficiency and in the way of a chain-reaction. 

The newest results obtained by Rabek and Rfinby (67) show that during dye sensitized singlet oxygen photo-oxidation of cis- and trans-polybutadiene rapid degradation ocour what has been indicated by viscosity (Fig.4) and Gel Permeation Chromatography (GPC)(Pig.5). 

A second form of photo-degradation was postulated in the absence of oxygen it was studied by performing experiments in an atmosphere of nitrogen. The reaction is slow and leads to a decrease in the intensity of the amylose-iodine stain and to an increase in the reducing power. 

A review of the photo-degradation of polystyrene includes a mechanism proposed to explain the breakdown of that polymer. A novel technique for following the extent of photo-oxidation of bulk polymer has been developed by Weir who measured the dielectric loss of films during irradiation in vacuum and in oxygen. Under these conditions the increases in dielectric constant were attributed to products of degradation, and measurement of the loss-peak due to carbonyl compounds provided a sensitive indicator of extent of reaction. - A study of the role of stabilizers showed that for specific types the stabilization mechanism involved the screening effect as well as the ability to quench excited states of the polymer. A study of photo-oxidation (A>300nm) of films of styrene-type copolymers produced a mechanism in which it was proposed that initiation of the... 

---