Polymer processing radiation-chemical methods

There are two basic methods for making polymer materials photo-chemically degradable.1,2 One method is to chemically incorporate a chromo-phore into the polymer chains. One commercially successful chromophore is the carbonyl group.1,2,7 Absorption of UV radiation leads to degradation by the Norrish type I and II processes or by an atom abstraction process (Scheme 1). Note that once radicals are introduced into the system, chain degradation occurs by the autoxidation mechanism (Scheme 2). 

The problem of stabilization in the broad meaning of the word is that of the conservation of the initial properties of polymer substances and materials under the most varied influences heat, radiation, mechanical and chemical influences, primarily oxidation and hydrolysis, and, finally, the influence of microorganisms. It is quite natural that in this effort we come up against all the variety of chemical and structural processes that occur during the breakdown of polymers, and we arrive at the conclusion that stabilization cannot be accomplished for all polymers by any single method. Hence, the particular problem that forms the basis for polymer breakdown must be defined in each case. 

Thus, different ways are suitable for AR formation in polymers, including purely chemical synthetic methods as well as radiation-initiated, photo- and mechano-chemically initiated processes. The choice of one or other depends on the chemical structure of the polymer, and the availability or lack of reactive functional groups in macromolecules [119]. 

The scission and crosslinking reactions have the greatest effect on the material properties of polymers and measurement of the radiation chemical yields of these two processes is very important for quantifying degradation of polymers by radiation(4). The main methods used to determine the yields of scission and crosslinking are listed in Table 2. 

Another class of membranes is the capillary-pore membranes. The process involves exposing a dense film to ionizing radiation (such as thermal neutrons) that degrades the polymer in specific areas allowing removal by chemical methods yielding uniform pores through the membrane. These membranes... 

Many challenging industrial and military applications utilize polychlorotriduoroethylene [9002-83-9] (PCTFE) where, ia addition to thermal and chemical resistance, other unique properties are requited ia a thermoplastic polymer. Such has been the destiny of the polymer siace PCTFE was initially synthesized and disclosed ia 1937 (1). The synthesis and characterization of this high molecular weight thermoplastic were researched and utilized duting the Manhattan Project (2). The unique comhination of chemical iaertness, radiation resistance, low vapor permeabiUty, electrical iasulation properties, and thermal stabiUty of this polymer filled an urgent need for a thermoplastic material for use ia the gaseous UF diffusion process for the separation of uranium isotopes (see Diffusion separation methods). 

Radiation-induced modification or processing of a polymer is a relatively sophisticated method than conventional thermal and chemical processes. The radiation-induced changes in polymer materials such as plastics or elastomers provide some desirable combinations of physical and chemical properties in the end product. Radiation can be applied to various industrial processes involving polymerization, cross-linking, graft copolymerization, curing of paints and coatings, etc. 

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