Oxygen assisted Chain Transfer

In Sect. 7,3.2, it was shown that trapped radicals decay via a chain process when the 

Such a chain process also occurs when the polymerization is carried out in an atmosphere which contains oxygen. The chain reaction not only causes enhanced oxidation of the polymer, it also induces enhanced mobility of the radical sites in the network. This shows up as an enhanced termination which reduces the overall rate of polymerization. 

This change in mechnism is caused by the strong reduction of the mobility of the 

Towards the end of the reaction, the rate reduction by oxygen diminishes again, presumably since the replenishment of oxygen is progressively suppressed by the 

The presence of oxygen also influences the apparent order of the rate with respect to light intensity. At an oxygen concentration of 2 ppm, an apparent order of 0.7 was found for HDDA at a double bond conversion of 0.3. This value was constant over 4 decades of light intensity variation. The deviation from the classical value of 

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Cytochrome c, a small heme protein (mol wt 12,400) is an important member of the mitochondrial respiratory chain. In this chain it assists in the transport of electrons from organic substrates to oxygen. In the course of this electron transport the iron atom of the cytochrome is alternately oxidized and reduced. Oxidation-reduction reactions are thus intimately related to the function of cytochrome c, and its electron transfer reactions have therefore been extensively studied. The reagents used to probe its redox activity range from hydrated electrons (I, 2, 3) and hydrogen atoms (4) to the complicated oxidase (5, 6, 7, 8) and reductase (9, 10, 11) systems. This chapter is concerned with the reactions of cytochrome c with transition metal complexes and metalloproteins and with the electron transfer mechanisms implicated by these studies. 

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