Grafting high-energy radiation

Another use is of minor proportions of polyfunctional aHyl esters, eg, diaHyl maleate, ttiaHyl cyanurate, and ttiaHyl isocyanurate, for cross-linking or curing preformed vinyl-type polymers such as polyethylene and vinyl chlotide copolymers. These reactions ate examples of graft copolymerization in which specific added peroxides or high energy radiation achieve optimum cross-linking (see Copolymers). 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

High-energy radiation is a non-selective process in that the energetic radiation will remove atoms and generate radical sites more or less at random. It is not possible to predict the site at which graft copolymerization may occur. 

Dobo, J. Graft copolymerization under the influence of high-energy radiation Magyar Kem. Lapja 13, 76 (1958). Chem. Abstr. 52, 17790 (1958). 

The modification of the properties of cotton cellulosic textile products, through free radical-initiated graft copolymerization reactions with vinyl monomers, has been investigated at the Southern Laboratory for a number of years (6, 9). In this chapter, we summarize the basic mechanisms and principles involved in free radical reactions of cellulose, initiated by high energy radiation, ceric ion in acidic solution, and aqueous solutions of ferrous ion and hydrogen peroxide. Some of the properties of fibrous cotton cellulose graft copolymers are also presented. 

The high-energy radiation forms macrocellulosic radicals that are stable in the crystalline areas of cellulose. These radicals can initiate reactions with vinyl monomers to yield grafted polyvinyl-cellulosic fibers with desired properties [522-524]. 

As discussed in the previous section, this book focusses on reactive polymer systems, from network-forming polymers to reactively modified polymer systems. Network polymers may be defined as polymer systems that contain chemical or physical networks between the constituent molecules of the system. Within the term reactively modified polymers we include polymer systems that have been modified by grafting, chemical reaction or high-energy radiation. Typically network or reactively modified polymers are manufactured by various... 

When high-energy radiation is used, the most important factor affecting the grafting efficiency is the radiation sensitivity of the monomer to be... 

Because, in most cases, the radicals generated on the surface are inadequate to afford graft chains with quantitative yields, the addition of a photosensitizer is essential. Once again, the reader s attention is directed to the fact that high-energy radiations such as y-rays are not regarded as photochemical means. 

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