Photodegradation, of polycarbonate

In this laboratory apparatus has been constructed to examine the photodegradation of polycarbonate with simultaneous control of the following variables l) minimum wavelength of light, 2) oxygen or nitrogen atmospheres, 3) relative humidity, and 4) state of prior hydrolysis of the sample. In addition, the temperature is controlled at 22-25 "C. 

All of the factors surveyed in this study have an effect on at least some of the reactions involved in the photodegradation of polycarbonate. 

The results from this survey indicate that a wide variety of reactions occur in the photodegradation of polycarbonate under natural weathering conditions. Both oxidative and non-oxidative processes are involved, but the oxidative reactions probably cause greater loss in physical properties. Accelerated aging studies should take into account the variables tested here. In particular, acceleration should not be accomplished by the use of very short wavelength light. 

Fukuda and Osawa [104] studied the photodegradation of polycarbonate films in air using the IR absorbance band at 1687 cm to monitor the photo-Fries reaction products. Only the short wavelengths of X = 260 and 280 nm showed any product formation longer wavelengths yielded no measurable... 

Fig. 10. Action spectra for photodegradation of polycarbonate at ambient temperature. Change in yellowness index from [105] change in absorbance from [104] change in quantum yield for chain scission from [96]...

Photodegradation of polycarbonate films exposed outdoors to longer wavelengths can be due to initiation mechanisms caused by the presence of impurities, as well as to the structural defects in the polymer [464,465, 638, 1507, 1528, 1742, 1848, 1849]. 

Before considering the experimental data, we may briefly consider some recent theoretical conq)utations 5 which shed new light on the nature of the excited states involved in photodegradation of polycarbonates. 

We outline here the main features of studies on the photodegradation of polycarbonate viewed from the surface point of view with particular reference to wavelengths > 290 nm. 

The lanthanides find some use as stabilizers for polymers. The coating of polycarbonate with a poly(vinyl alcohol) film containing CeCl3 inhibits photodegradation of the polycarbonate.151 The naphthenates of cerium, lanthanum and yttrium act as thermal stabilizers for polyorgano-siloxanes.152... 

It has been found that the photodegradation of several polders such as poly(vinyl chloride)(115).polyisoprene (109, 116).bisphenol A polycarbonate (117) is sensitized by peroxides. 

Two distinct mechanistic pathways have been proposed on the basis of the results obtained and they are shown in Schemes 13 and 14 for short and long wavelength irradiation conditions. All the products shown were identifiable. At high humidity the kinetics of the photooxidation of polycarbonate is influenced to some extent in that on short-wavelength irradiation only products which are soluble in water appear to be produced. Furthermore, the presence of the moisture has an accelerating effect on photodegradation of the polymer. The life expectancy of stabilised polycarbonate is expected to be at least... 

The results from the previous sections confirm that all the variables surveyed in this study have measurable effects on the photodegradation of bisphenol A polycarbonate. The first part of this discussion will summarize these effects. The second part will examine possible reaction pathways to the products seen in this and other works and suggest how some of the variables could affect these reactions. 

Miscellaneous.—Recent papers have reported the photodegradation of urethanes,247 the photolysis of organopoly(silanes),248 and the photodegradation of bisphenol-A-polycarbonate.249 The degradation in the last study was shown to involve chain scission, cross-linking, and the photo-Fries rearrangement. 

Pickett JE. Influence of photo-Fries reaction products on the photodegradation of bisphenol-A polycarbonate. Polym Degrad Stab 2011 96 (12) 2253-2265. 

Photodegradation of Cu-EDTA complexes Polycarbonate microchannel reactor 10 mW UV-LED (Nichia. 365 nm) [8]... 

The photodegradation of unstabilized bisphenol A polycarbonate films is described as an autoaccelerating process initiated by formation of products arising from a formal photo-Fries reaction. Oxidation also contributes as an additional photodegradation pathway. Photosensitive polymers... 

Diepens M, Gijsman P. Photodegradation of bi-sphenol a polycarbonate. Polym Degrad Stab 2007 92 397 06. 

Photodegradation of bisphenol-A-epichlorhydrin [1225], poly(dian carbonates) [1738] and of polycarbonate blends with polypropylene [1282] and poly(methyl methacrylate) has also been described [673, 1645]. 

Sulphur dioxide (SO2) and nitrogen dioxide (NO2) cause accelerated photodegradation of poly(tert-butyl methacrylate) [599], poly(methyl methacrylate), polystyrene, poly(vinyl fluoride), poly(N-vinylpyrrolidone), polycarbonate, polyamides and butyl rubber [927, 931, 1016, 1078, 1080-1082, 1084, 1088, 1091]. 

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