Oxygen-induced radical

One way in which most polymers do decay is by the action of oxygen in the air and of light You will be familiar with the way that some polymers go yellow after a time and some become brittle. Coloured plastics, in particular, absorb light and oxygen-induced radical reactions follow. The polymer becomes too cross-linked and loses flexibility. One ingenious application of this natural process helps to degrade the polythene rings that hold cans of beer in packs. These are often discarded and decay quite quickly because some carbon monoxide has been incorporated into the polyethylene to make it more sensitive to photolysis. 

Keeping in mind that ESR knowledge can be useful for the orthopedic or biomaterials community, this chapter starts with the basic principle of ESR and provides ESR data on the radicals generated, propagated, and terminated in UHMWPE. Emphasis is given on the short-and long-term oxidation results and on identification of the peroxy and oxygen-induced radicals. ESR results on vitamin E-doped UHMWPE and quantitative ESR are also presented. 

LONG-LIVED OXYGEN-INDUCED RADICAL IN UHMWPE... 

FIGURE 29.10 ESR spectnim recorded as a function of time at room temperature to monitor the growth of the oxygen-induced radical. (A) GUR 4150 bar irradiated with X-ray for 1.3 hours in air and stored in air at room temperature. (B) GUR 4120 was gamma irradiated in an evacuated quartz tube and then stored for 6 years at 75°C in a vacuum. The sample was then removed from the mbe to allow oxidation to occur at room temperature. 

Growth and decay of oxygen induced radicals and decay of primary radicals. 

Jahan MS, Durant J. Investigation of the oxygen-induced radicals in ultra-high molecular weight polyethylene. Nucl Instr Meth Phys Res 2005 B 236 166-71. 

J.M. Shah, M. Fuzail. Examination of the long-lived, oxygen-induced radicals in irradiated ultra-high molecular weight polyethylene. Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 265(1), 67-71, December (2007). 

The ultimate fate of the oxygen-centered radicals generated from alkyl hydroperoxides depends on the decomposition environment. In vinyl monomers, hydroperoxides can be used as efficient sources of free radicals because vinyl monomers generally are efficient radical scavengers which effectively suppress induced decomposition. When induced decomposition occurs, the hydroperoxide is decomposed with no net increase of radicals in the system (see eqs. 8, 9, and 10). Hydroperoxides usually are not effective free-radical initiators since radical-induced decompositions significantly decrease the efficiency of radical generation. Thermal decomposition-rate studies in dilute solutions show that alkyl hydroperoxides have 10-h HLTs of 133—172°C. 

Oxygen-centered radicals are arguably the most common of initiator-derived species generated during initiation of polymerization and many studies have dealt with these species. The class includes alkoxy, hydroxy and aeyloxy radicals and tire sulfate radical anion (formed as primary radicals by homolysis of peroxides or hyponitrites) and alkylperoxy radicals (produced by the interaction of carbon-centered radicals with molecular oxygen or by the induced decomposition of hydroperoxides). 

Moyana, T. and Lalonde, J.M. (1991). Carrageenan-induced intestinal injury, possible role of oxygen free radicals. Ann. Clin. Lab. Sci. 21, 258-263. 

Mutoh, H., Ota, S., Hiraishi, H., Ivey, K.J., Terano, A. and Sugjmoto, T. (1990a). Relationships between divalent metals and oxygen ftee radicals in ethanol-induced damage to cultured rat gastric mucosal cells. Gastroenterology 98, A94. 

Takeuchi, K., Ueshima, K., Hironaka, Y., Fujioka, Y., May-sumoto, J. and Okabe, S. (1991a). Oxygen free radicals and lipid peroxidation in the pathc nesis of gastric mucosal lesions induced by indomethadn in rats. Relation to gastric hypermotility. Digestion 49, 175-184. 

Tkeshelashvili, L.K., T.M. Reid, T.J. McBride, and L.A. Loeb. 1993. Nickel induces a signature mutation for oxygen free radical damage. Cancer Res. 53 4172-4174. 

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