Poly , radiolysis

The most radiation-stable poly(olefin sulfone) is polyethylene sulfone) and the most radiation-sensitive is poly(cyclohexene sulfone). In the case of poly(3-methyl-l-butene sulfone) there is very much isomerization of the olefin formed by radiolysis and only 58.5% of the olefin formed is 3-methyl-l-butene. The main isomerization product is 2-methyl-2-butene (37.3% of the olefin). Similar isomerization, though to a smaller extent, occurs in poly(l-butene sulfone) where about 10% of 2-butene is formed. The formation of the olefin isomer may occur partly by radiation-induced isomerization of the initial olefin, but studies with added scavengers73 do not support this as the major source of the isomers. The presence of a cation scavenger, triethylamine, eliminates the formation of the isomer of the parent olefin in both cases of poly(l-butene sulfone) and poly(3-methyl-1-butene sulfone)73 indicating that the isomerization of the olefin occurred mainly by a cationic mechanism, as suggested previously72. 

Hydrogen, which is a major product in the radiolysis of most hydrocarbon polymers, is only a minor product in the radiolysis of poly(olefin sulfone)s, although it is of the largest yield between the minor products. Hydrogen is formed by H atoms combination or by an H atom abstracting hydrogen... 

Kaplan78 studied the X-ray radiolysis of poly(a>-chloroolefin sulfone)s and found that the chlorine-containing polymers are less sensitive to radiation than the non-chlorine containing species. He found that dehydrochlorination is a significant reaction in the radiolysis of poly(to-chloroolefin sulfone)s, but it is not a necessary one in order to lose... 

Bowden and Thompson83 studied the degradation of thin films of various poly(olefin sulfone)s of low olefins due to radiolysis by electron beams at 20 °C. All samples decreased in thickness, indicating scission and depropagation. 

Polychloromethylsulphonylbiphenyls, mass spectra of 154, 155 Polyenes, synthesis of 771 Polymerization, of sulphoxides 846 Polymer-supported reagents 928 Polymorphonuclear leukocytes 854 Poly(olefin sulphonejs, radiolysis of 916-922 Polysulphones, radiolysis of 913 Population analysis 14, 15, 21, 22 Propargylic sulphenates, rearrangement of 736-739... 

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

Temperature dependence (related to the temperature dependence of the conformational structure and the morphology of polymers) of the radiation effect on various fluoropolymers e.g., poly (tetrafluoroethylene-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkylvinylether), and poly(tetrafluoroethylene-co-ethylene) copolymers has been reported by Tabata [419]. Hill et al. [420] have investigated the effect of environment and temperature on the radiolysis of FEP. While the irradiation is carried out at temperatures above the glass transition temperature of FEP, cross-linking reactions predominate over chain scission or degradation. Forsythe et al. [421]... 

This sequence of formation of radical cation which is followed by a C—S bond scission into alkyl radical and alkyl sulfonyl cation was previously suggested by the same authors for the radiolysis of poly(olefin sulfone)s in the solid state and was confirmed by scavenger studies . Seavengers are ineffeetive in erystalline solids such as dialkyl sulfones and hence eould not be used in this study. 

Recently, Chaudhari compared the activity of dispersed nanosized metal particles prepared by chemical or radiolytic reduction and stabilized by various polymers (PVP, PVA or poly(methylvinyl ether)) with the one of conventional supported metal catalysts in the partial hydrogenation of 2-butyne-l,4-diol. Several transition metals (e.g., Pd, Pt, Rh, Ru, Ni) were prepared according to conventional methods and subsequently investigated [89]. In general, the catalysts prepared by chemical reduction methods were more active than those prepared by radiolysis, and in all cases aqueous colloids showed a higher catalytic activity (up to 40-fold) in comparison with corresponding conventional catalysts. The best results were obtained with cubic Pd nanosized particles obtained by chemical reduction (Table 9.13). 

Gamma radiolysis of simple carboxylic acids and N-acetyl amino acids results in loss of the carboxyl group with formation of carbon monoxide and carbon dioxide. In the carboxylic acids, the ratio of C0/C02 produced is approximately 0.1, while in the N-acetyl amino acids the ratio is much smaller. In the poly carboxylic acids and poly amino acids, radiolysis also results in the loss of the carboxyl group, but here the ratio of C0/C02 is greater than 0.1. Incorporation of aromatic groups in the poly amino acids provides some protection for the carboxyl group. The degradation of the poly acids is believed to involve radical and excited state pathways. 

Table VII. G-values for carbon monoxide and carbon dioxide formed on radiolysis of poly acids at 303 K...

As with the aliphatic carboxylic acid model compounds, the major volatile product observed on gamma radiolysis of the poly acids is carbon dioxide. However, the carbon dioxide yields are somewhat larger than those observed for the model compounds. 

The only radical intermediate observed for poly methacrylic acid was the propagating radical formed by main chain scission. This observation is similar to that noted for gamma radiolysis of poly methylmethacrylate, where the propagating radical is also found as the only stable radical intermediate following radiolysis at 303 K. In both cases the propagating radical is formed by -scission following the loss of the side chain, resulting in formation of the unstable tertiary radical. 

However, the major reaction following radiolysis of poly glutamic acid is decarboxylation (Hill, D.J.T. Ho, S.Y. O Donnell, J.H. Pomery, P.J. Radiat. Phvs. Chem.. submitted for publication). 

Two stable radical intermediates are observed following gamma radiolysis at 303 K. The alpha carbon radical VIII and the side chain radical IX are formed in approximately equal yields, with the total G-value for radical production equal to 3.2. This value is similar to that observed for the poly acids. The observed radicals are those which would be expected on the basis of the aliphatic carboxylic acids and previous studies of the poly amino acids with aliphatic side chains. 

In the poly carboxylic acids, carbon dioxide is the major product of radiolysis, but the carbon monoxide yields are greater than they are for the aliphatic carboxylic acids. However, the radical yields are not greater than expected on the basis of the model compounds, which suggests that excited states play an important role in the degradation of these poly acids. 

Figure 50, Schematic function of the t-Bocstyrene resist, S is a sensitizer such as diphenyliodonium hexafluoroarsenate which undergoes radiolysis to produce a strong acid (A), The acid attaches the side chain of the poly-(t-Bocstyrene) where it catalyzes acidolysis of the carbonate to liberate CO2 and isobutylene and free the phenolic hydroxyl group to produce poly (p-hydroxystyrene) in the exposed areas of the resist film. The acid A is a catalyst and can cleave many carbonate groups.

Monkman AP, Burrows HD, Hamblett I, Navaratnam S, Scherf U, Schmitt C (2000) The triplet state of the ladder-type methyl-poly(p-phenylene) as seen by pulse radiolysis-energy transfer. Chem Phys Lett 327 111... 

Irradiation with 7-rays was also used to synthesize bimetallic nanoparticles. Remita et al. synthesized poly(vinyl alcohol) (PVA)-stabilized Ag/Pt bimetallic nanoparticles by radiolysis of an aqueous mixture of Ag2S04 and K2PtCl4 at a concentration of 10-4 mol dm-3. A typical Ag plasmon absorption band is observed at —410 nm with only low intensity at the mole ratio of Ag Pt = 60 40, indicating the formation of Ag/Pt bimetallic nanoparticles. Polyfacrylic acid) was also used as the stabilizer, although the resulting UV-Vis spectra were quite different. 

Table II. Yields of Butene Isomers from the Radiolysis of Poly (1-Butene Sulfone) at 30 °C...

We have studied the alkane and alkene yields from the radiolysis of copolymers of ethylene with small amounts of propylene, butene and hexene. These are examples of linear low density polyethenes (LLDPE) and models for LDPE. Alkanes from Ct to C6 are readily observed after irradiation of all the polymers in vacuum. The distribution of alkanes shows a maximum corresponding to elimination of the short-chain branch. This is illustrated in Figure 8 for the irradiation of poly (ethylene-co-1-butene) containing 0.5 branches per 1,000 carbon atoms at 20 C. 

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