Polycarbonates photodegradation

Differential Ultraviolet Spectroscopy as an Aid in Studying Polycarbonate Photodegradation... 

The chemical processes involved in polycarbonate photodegradation are not well defined. Much early work concentrated on the photo-Fries reaction, which involves rearrangement to... 

Rivaton A. Recent advances in bisphenol-A polycarbonate photodegradation. Polym Degrad Stab 1995 49 163-179. 

Figure 15. Schematic outline of principal features of the nature of the excited state involved in Bisphenol A polycarbonate photodegradation.

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... 

Because of its excellent physical properties, polycarbonate is specified for a number of engineering uses. Some of these may involve significant exposure to light. As an aromatic polymer, polycarbonate absorbs significantly in the near UV and is thus susceptible to photodegradation. 

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. 

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. 

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. 

---