Other Photochemical Degradation Mechanisms

In addition to autocatalytic oxidative degradation, selected polymers undergo additional photochemical reactions, depending on their structure and environment  

As mentioned above, PVC degrades to form polyenes (Eq. 3), which subsequently imdergo backbone degradation (scheme 4).  

The photochemical Fries rearrangement can occur in polycarbonates, polyurethanes, epoxies, and other polymers with suitable structures. An example is shown 

A more complete listing of polymer photochemical reactions can be found in many of the excellent monographs that describe the photochemistry of poly- 

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PROBABLE FATE photolysis direct photochemical degradation in the atmosphere or in the upper layers of surface waters should not be an important fate process half-life for the atmospheric reaction with photochemically produced hydroxyl radicals 10 hrs oxidation could occur, but too slow to be important hydrolysis gradual hydrolysis of carbon-chlorine bond is a probable principle fate mechanism, can be expected in comparison to other chlorine containing compounds, half-life for this pH independent process 0.5-2 yrs volatilization not important, volatilization from water should be a slow process half-life from a model pond 1 lyrs, volatilization from the soil to the atmosphere might occur, but will be a slow process, volatilization from moist soil should not be an important fate process sorption possible importance as catalyst for hydrolysis biological processes biodegradation not expected to be an important fate process, but there is not enough data to draw a conclusion... 

Associating CB nanoparticles with titania in appropriate ratios [123], an enhanced photochemical stability, along with excellent mechanical properties, was reached due to combined effects of the nanofillers, despite other previous smdies that reported on the fast rate of photochemical degradation of PE-titania nanocomposites (17), faster than in pure polymer. 

Using neutral (pH 7) hydrogen peroxide Oki et al. [44] isolated methoxy hydroquinone and methoxy benzoquinone from the reaction of vanillin and acetovanillone with hydrogen peroxide. Other p-hydroxybenzaldehydes were degraded in a similar way. Hirashima and Sumimoto [45] obtained evidence for the presence of quinones in mechanical pulps, using a photochemical reaction with acetaldehyde. 

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