Oxygen, polymer weathering

Chlorosulfonated polyethylene (CSM, CSPR) n. Polyethylene which has been reacted with a mixture of chlorine and sulfur dioxide under ultraviolet light irradiation. Polymer may be vulcanized to form a product with good ozone, heat, oxygen and weathering resistance. It is produced by simultaneous treatment, with... 

Because of the inorganic nature inherent in the strings of sulfur atoms in their backbones, these polymers have excellent resistance to hydrocarbon solvents that can swell common hydrocarbon elastomers. They also have good resistance to moisture, oxygen, and ozone, good weatherability, and better-than-average low temperature properties.62... 

The rate of oxygen uptake of PA6 and PBT was determined in duplicate (Figure 3). Both polymers oxidize and show a linear relation between weathering time and oxygen uptake without an induction time. The oxygen uptake rate is a little higher for PBT than for PA6. 

In the case of PBT the conversion of oxygen into CO and CO2 is independent of the weathering time. For PA6, after an oxygen uptake of about 600 mmol/kg, which corresponds to a weathering time of 100-150 hours, an increase in the CO2 formation rate was observed. The conversion of oxygen into CO is about 5% and into CO2 about 10%. For both polymers CO can be formed by photolysis, but in the case of PA6, CO2 can only be formed by oxidation. 

Photochemically induced H-abstraction includes the electronically excited nitrox-ide pNO ] and occurs even at room temperature. The activation energy was reported to be 21 kJ/mol. The quantum yield is ca. 0.2 with light of wavelength <360 nm. Because of the air present during weathering of polymers, it is likely that the excited nitroxide is efficiently quenched by oxygen [189] and the photochemical formation of NOH is only negligible (Eq. 32, pathway a) ... 

Termination processes in weathering polymers include a variety of potential reactions of free radicals with one another. When the oxygen concentration is high, the predominant termination reaction (Equation 4.14) is usually the formation of unstable tetroxide intermediates (for mechanisms of decomposition of tetroxides, see Section 4.B.2) ... 

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