Classification of Polymers with respect to Reactivity toward Nitrogen Oxides

Classification of Polymers with respect to Reactivity toward Nitrogen Oxides 

A general review of the influence of pollutants on polymers has been presented by Jellinek and co-workers [1]. Therein the characterisation of the reactivity of polymeric materials toward aggressive gases is given. Various polymers were used as films of 20-pm thickness. In most cases, the thickness is sufficiently small to exclude diffusion as the determining factor of pollutant action. Films were investigated under different conditions  

For nitrogen dioxide (NO ), the exposure of samples was usually realised under a pressure of 15 mm Fig during 30 hours at 308 K. However, in the case of Nylon 66 and butyl rubber, NO pressure was lowered to 1 mm Hg during 30 minutes. Polyisoprene and polybutadiene were exposed to NO during 5 minutes under a pressure of 1 mm Hg. As a light source (A, 290 nm), a mercury lamp was used. The intrinsic viscosity of polymer solutions was measured before and after exposure of samples in the chosen conditions. The high concentration of NO in these situations was used to confirm that certain effects could be observed for a reasonable time. 

Polymers can be divided into two main classes on the basis of their reactivity to NO [1]. Saturated polymers such as polyethylene (PE) and polypropylene (PP) belong to the first group, but Nylon 66 does not. The second group covers elastomers. Butyl rubber (BR) undergoes scissions of the main chain, and polybutadiene is extensively cross-linked under the action of NO. These elastomers have approximately the same reactivity to NO as to ozone. All films exposed to NO become yellow, and their infrared (IR) spectra show that nitro groups enter into macromolecules. In polyvinylchloride in the presence of NO, a decrease in the amount of chlorine, along with the appearance of nitro and nitrite groups, are observed from IR spectra. 

Extrapolation was used for estimation of the scission average number S under the action of aggressive gases at concentrations of 1-5 ppm within 1 hour [1]. This value is given by the equation  

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