Differentiation of hydroperoxide groups by reactions with nitric oxide

2 Differentiation of hydroperoxide groups by reactions with nitric oxide 

Nitric oxide (NO) does not react with polyolefins however, hydroperoxide (OOH) and hydroxyl (OH) groups react with NO (in the absence of oxygen) 

During the exposure of oxidized samples of nitric oxide (NO) at — 20°C, the clearly visible absorption at 3400 cm (OOH/OH) disappears. The NO reaction time required for complete reaction is from 16 h for thin films (25-50 pm) to about 30 h for thicker films (up to 150 pm). Photo-oxidized polyolefin films (up to 150 pm) require up to 150h exposure. 

The direct use of nitric oxide (NO) reactions to identify and quantify hydroxyl (OH) and/or hydroperoxy (OOH) groups is complicated by the formation of equimolar mixtures of nitrates (with absorption bands at 1630, 1302, 1290, 1278 and 860 cm ) and nitrites (with a strong absorption band at 1645, and weak bands at 780-760 cm )  

In Table 10.17, IR data for model nitrates and nitrites are presented. 

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For other polymers, differentiation of hydroperoxide groups by reaction with nitric oxide is very limited. For example, polyamides react directly with nitric oxide, obscuring any products for oxidation of the polymer. Unsaturated polymers such as polybutadiene and polyisoprene also react directly with nitric oxide even at — 20°C, giving nitrocompounds which interfere with the identification of oxidation products. 

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