Radiolytic polymerization

Strahlenpolymerisation radiation polymerization, radiation-induced polymerization, radiolytic polymerization... 

Phenomenological evidence for the participation of ionic precursors in radiolytic product formation and the applicability of mass spectral information on fragmentation patterns and ion-molecule reactions to radiolysis conditions are reviewed. Specific application of the methods in the ethylene system indicates the formation of the primary ions, C2H4+, C2i/3+, and C2H2+, with yields of ca. 1.5, 1.0, and 0.8 ions/100 e.v., respectively. The primary ions form intermediate collision complexes with ethylene. Intermediates [C4iZ8 + ] and [CJH7 + ] are stable (<dissociation rate constants <107 sec.-1) and form C6 intermediates which dissociate rate constants <109 sec. l). The transmission coefficient for the third-order ion-molecule reactions appears to be less than 0.02, and such inefficient steps are held responsible for the absence of ionic polymerization. 

Radiolytic ethylene destruction occurs with a yield of ca. 20 molecules consumed/100 e.v. (36, 48). Products containing up to six carbons account for ca. 60% of that amount, and can be ascribed to free radical reactions, molecular detachments, and low order ion-molecule reactions (32). This leaves only eight molecules/100 e.v. which may have formed ethylene polymer, corresponding to a chain length of only 2.1 molecules/ ion. Even if we assumed that ethylene destruction were entirely the result of ionic polymerization, only about five ethylene molecules would be involved per ion pair. The absence of ionic polymerization can also be demonstrated by the results of the gamma ray initiated polymerization of ethylene, whose kinetics can be completely explained on the basis of conventional free radical reactions and known rate constants for these processes (32). An increase above the expected rates occurs only at pressures in excess of ca. 20 atmospheres (10). The virtual absence of ionic polymerization can be regarded as one of the most surprising aspects of the radiation chemistry of ethylene. 

Consider alternative polymerization processes in solid state, inducing the polymerization reaction of N3P3CI6 thermally [40-42],photochemically [61, 67,68],y-radiolytically [66,210], using X-rays [74,75,90] or electron irra-... 

The radiolysis of olefinic monomers results in the formation of cations, anions, and free radicals as described above. It is then possible for these species to initiate chain polymerizations. Whether a polymerization is initiated by the radicals, cations, or anions depends on the monomer and reaction conditions. Most radiation polymerizations are radical polymerizations, especially at higher temperatures where ionic species are not stable and dissociate to yield radicals. Radiolytic initiation can also be achieved using initiators, like those used in thermally initiated and photoinitiated polymerizations, which undergo decomposition on irradiation. 

Degradation Products from the Radiolysis of HDEHP Systems. The main radiolytic degradation products are in the organic phase, mono(2-ethylhexyl) phosphoric acid (H2MEHP), 2-ethylhexanol, and polymeric species, but also a certain amount of ortho phosphoric acid (H3P04) was detected in the aqueous phase. The nature of the short compounds identified in the gas fraction was classical H2, unsaturated and saturated hydrocarbons (from 1 to 4 carbons), 02, and N2 (10, 74, 158-160, 164). 

Influence of the Aqueous Phase The presence of an aqueous phase during irradiation increases the radiolytic destruction of HDEHP (158, 160) and leads to an increase of the polymeric species, particularly under acidic conditions. 

Concerning strontium extraction, the principal radiolytic effect was a two- to threefold decrease (158). Schultz explained this effect by the polymerization of HDEHP with H2MEHP via hydrogen bonding, making HDEHP molecules either unavailable or less available for binding with strontium. According to Tachimori (163), the... 

Regeneration of impurity is dictated by the failure to observe any acceleration in the rate of polymerization with conversion, of most monomers studied, because of consumption of inhibitor. Radiolytic formation of inhibitor is suggested by the fact that in most monomers studied,... 

The chemical methods for the preparation of nanomaterial could be categorized as either template-directed or template-free. The template synthesis methods commonly used for the production of one-dimensional nanostructured PANI are further subdivided into hard template (physical template) synthesis and soft template (chemical template) synthesis approach according to the solubility of the templates in the reaction media. Non-template routes for the synthesis of one-dimensional nanostructured PANI such as rapid-mixing reaction method, radiolytic synthesis, interfacial polymerization, and sonochemical synthesis have also been reported [56], Other approaches like combined soft and hard template synthesis are also known. An overview of hard-template, soft-template, and template-free procedures are presented in the following paragraphs. 

Thble 6.5 G-Values (100-eV yields of initiating radicals) in Radiolytic Free-Radical Chain Polymerization... 

Thermal polymerizations of vinylic crystalline monomers giving isotactic or syndiotactic crystalline polymers are rare. More frequent are photolytical and radiolytical studies. The crystallographic packing requirements are most stringent. Clearly, the polymer chains cannot exit the crystal. They must therefore be able to accommodate with the monomer structure. Despite enormous efforts only a few... 

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