Substitution Reactions of Saturated Polymeric Hydrocarbons

It is often desirable to replace hydrogens with halogens. Fluorimtion of polyethylene can be carried out in the dark by simply exposing the polymer, either in sheet or in powder form, to fluorine gas. The reaction is exothermic and it is best to dilute the gas with nitrogen to allow a gradual introduction of the fluorine and avoid destruction of the polymer. In this manner, however, only the surface layers are fluorinated and the substitutions occur only a few molecular layers deep. 

In surface fluorination with vacuum ultraviolet glow discharge plasma, the photon component of the plasma enhances the reactivity of the polymer surfaces toward fluorine gas  

The surface free radicals can also cause elimination of hydrogen radicals and formation of double bonds. Whether as free radicals or through unsaturation, the units are now more reactive toward fluorine. 

A film that is three mils thick can be completely fluorinated on a 100-mesh phosphor bronze gauze, if the reaction is allowed to proceed for several days. Fluorination can also be carried out 

CHAPTER 8 In direct fluorination of powdered high-density polyethylene with the gas, diluted with helium 

A film that is 3 mil thick can be completely fluorinated on a 100-mesh phosphor bronze gauze, if the reaction is allowed to proceed for several days [135]. Fluorination can also be carried out with mercuric or cupric fluorides in hydrofluoric acid. The reaction must be carried out at 110°C for 50 h. As much as 20% of fluorine can be introduced [136]. 

In direct fluorination of powdered high-density polyethylene with the gas, diluted with helium or nitrogen, the accompanying exotherm causes partial fusion. In addition, there is some destruction of the crystalline regions [137]. On the other hand, fluorination of single crystals of polyethylene can result in fluorine atoms being placed on the carbon skeleton without disruption of the crystal structure. The extent of cross-linking, however, is hard to assess [138]. The reaction has all the characteristics of free-radical mechanism [139]  

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