Radiation-induced direct polymer grafting

The only way to apply chemically bonded thin perfluorosulfonic acid layer onto the surface of an inert support is to graft perfluorinated functional monomers onto perfluorinated polymers. Some features of radiation-induced graft copolymerization of PFAVESF onto fluoropolymers were investigated. The studies showed that neither irradiation of a fluoropolymer-PFAVESF mixture (direct grafting) or interaction of PFAVESF with previously irradiated fluoropolymers (preirradiation grafting) yielded the grafted copolymers. It was assumed that this is connected with the low activity of PFAVE in radical polymerization. A special method has been developed for the synthesis of grafted copolymer. Previously irradiated fluoropolymer powders were used to prevent waste of PFAVESF. 

Nasef, M.M. 2008. Fuel cell membranes by radiation-induced graft copolymerization Current status, challenges, and future directions. In Polymer Membranes for Fuel Cells, eds. S.M.J. Zaidi and T. Matsuura, pp. 87-114. Springer Science New York. 

The foregoing remarks indicate the diversity of subjects which may be covered by a review on polymer reactions. Because of space limitations, however, several topics within this range, such as photochemistry, crosslinking reactions and syntheses of block copolymers, have been omitted. The formation of graft copolymers, where grafting is preceded by chemical modification of the back bone, is included but not radiation-induced or other direct grafting reactions. Some of these topics are covered elsewhere in this volume. 

The previously discussed principles of grafting-to and grafting-from can also be applied for the modification of polymer surfaces with polymer brushes. However, the binding of linkers and polymerization initiators to polymer surfaces is not as straightforward as it is for oxidic inorganic materials. Thus, dedicated pretreatments are usually necessary. These may include rather harsh reaction conditions due to the chemical inertness of many polymers (see Chapter 3). Alternatively, radiation treatment of polymers (to form radicals) followed by exposure to air may be used to form peroxides and hydroperoxides, which can be directly used as initiators for thermally or ultraviolet-induced graft polymerizations [16,17] (see Chapter 2). 

The title of this chapter has also been slightly amended, Reactions on Polymers being preferred to Reactions of Polymers because the former is more specific. Nevertheless, a great diversity of material could still be included under the new title and as before a measure of selectivity has been imposed. Again, photochemistry, crosslinking reactions, and direct radiation or radical-induced grafting reactions have been omitted. 

Grafting induced by radiation methods can be achieved either after preirradiation or simultaneously during the irradiation. In the latter, polymer film is embedded in a monomer solution which is directly grafted during the irradiation process. 

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