Oxygen photo-oxidative degradation

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). 

Rabek found in his investigations of the photo-oxidative degradation of cis-l,4-polyisoprene in solution that benzophenone [496, 502], Michler s ketone (4,4 -bis-(dimethylamino)-benzophenone) [508] and thiobenzo-phenone [494, 495] sensitize the reaction (Fig. 19). In the absence of oxygen benzophenone promotes the formation of microgel. 

The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed. A study has appeared of the effect of P-carotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between /S-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer. At 400 nm... 

In conclusion, singlet oxygen plays a role in the photo-oxidative degradation of polymers containing olefinic unsaturations. Polymers that do not contain these groups, e.g. poly(vinyl chloride), poly(methyl methacrylate), polystyrene, etc., are unreactive [24]. 

Plastic garbage made of polyethylene is biologically degraded in the environment only if the photo-oxidative degradation initiated by UV radiation and oxygen has progressed to a large extent already. Unexposed to... 

Light radiation increases the brittleness of polyolefins and seriously lowers their physical properties, mainly mechanical properties. Such degradation is more pronounced in the presence of oxygen. All modifications produced by photo-oxidative degradation are similar to those produced by thermal degradation and, are accelerated by an increase in light intensity [19] and temperature [20]. 

Oxygen diffuses only into amorphous regions of a polymer making them more susceptible to photo-oxidative degradation. 

Photo-oxidative degradation of electron-beam and UV cured di- and triacrylate resin films has been investigated [104,105]. The nature of the curing process and the photoinitiator are important in controlling the rate of photooxidation of the resin films. The inherent stability of the resin structure is dependent on the number of methylene protons which are alpha to the polyether oxygens. Electron beam cured resins are initially more photostable but eventually attain the same oxidation rate as for UV cured films. 

Polystyrene can form a charge-transfer (CT) complex with molecular oxygen [36, 1386, 1610, 1611, 1781, 1793, 1794, 2301]. The absorption band of the CT complex extends from 350 nm toward longer wavelengths [1610]. High oxygen pressure promotes the formation of the CT complex [1794] and the rate of photo-oxidation, but does not influence the mechanism of photo-oxidative degradation [1610, 1793]. The concentration of the CT complex depends on two factors ... 

Initiation of the photo-oxidative degradation is due to the presence of internal chromophoric impurities, which can absorb UV radiation (section 3.11.1.2). The nature of these chromoirfiores has been the subject of several investigations and considerable controversy. Figure 3.50 shows the effect of UV irradiation in oxygen (1 atm) on the various polystyrenes. 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

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