Poly irradiation studies

Zhang, Z., Ito, Y. (1991) Microstructure of gamma-ray irradiated poly-ethylenes studied by positron annihilation . Radial. Phys. Chem. 38(2), 221. 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

These pioneer studies laid dormant until 1977 and, influenced by Kondo and colleagues [59] reports on the synthesis of po]y(vinylsulfonium yiide) with a trivaient sulfur attached directly to the polymer chain, poly[ethyl-vinylsulfonium bis-(methoxycarbonyl) methylide] (Scheme 25) was prepared by irradiation of a benzene... 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

Polymer grafting can be used to alter chemical and physical properties of a homopolymer. For example, Sawhney and Hubbell [18] grafted polyethyleneoxide to poly L-lysine to enhance biocompatibility of polylysine and improve the polylysine-alginate capsules. Stevenson and Sefton [19] modified alginate by grafting it with hydroxyalkyl methacrylate, again to improve the biocompatibility and to allow for polymerization by means of y-irradiation. Covalently modified (co)-polymers have not been evaluated in this study. 

This study will show an approach to materials which have many of the desirable features of the poly(phthaladehyde)-onium salt imaging system but do not suffer from the problem of spontaneous gaseous material evolution upon irradiation. The new polyformal-based imaging systems all have a "built-in" thermal activation requirement which allows for image self-development outside of the exposure tool. 

Photochemical reactions of the pyrimidine polymers in solution were studied to determine the quantum yields of the intramolecular photodimerization of the pyrimidine units along the polymer chains. Photoreactions of the polymers were carried out in very dilute solutions to avoid an intermolecular(interchain) photodimerization. Quantum yields determined at 280 nm for the polymers (1-6 in Figure 1) are listed in Table I. The quantum yield of the 5-bromouracil polymer [poly(MAOU-5Br)] could not be determined because of side reactions of the base during the irradiation. 

Recent studies on LET effects In 2 mm thick samples of polymers have shown no difference between fast neutron and Co60 gamma irradiations for poly(olefIns) (32), a small difference for... 

The high photostability and acute fluorescence intensity are two major features of DDSNs compared to dye molecules in a bulk solution. The early DDSN studies have focused on these two properties [8, 13]. For example, Santra et al. studied the photostability of the Ru(bpy)32+ doped silica nanoparticles. In aqueous suspensions, the Ru(bpy)32+ doped silica nanoparticles exhibited a very good photostability. Irradiated by a 150 W Xenon lamp for an hour, there was no noticeable decrease in the fluorescence intensity of suspended Ru(bpy)32+ doped silica nanoparticles, while obvious photobleaching was observed for the pure Ru(bpy)32+ and R6G molecules. To eliminate the effect from Brownian motion, the authors doped both pure Ru(bpy)32+ and Ru(bpy)32+-doped silica nanoparticles into poly(methyl methacrylate). Under such conditions, both the pure Ru(bpy)32+ and Ru(bpy)32+ doped silica nanoparticles were bleached. However, the photobleaching of pure Ru(bpy)32+ was more severe than that of the Ru(bpy)32+ doped silica nanoparticles. 

Radiation Induced Reactions. Graft polymers have been prepared from poly(vinyl alcohol) by the irradiation of the polymer-monomer system and some other methods. The grafted side chains reported include acrylamide, acrylic acid, acrylonitrile, ethyl acrylate, ethylene, ethyl methacrylate, methyl methacrylate, styrene, vinyl acetate, vinyl chloride, vinyl pyridine and vinyl pyrrolidone (13). Poly(vinyl alcohols) with grafted methyl methacrylate and sometimes methyl acrylate have been studied as membranes for hemodialysis (14). Graft polymers consisting of 50% poly(vinyl alcohol), 25% poly(vinyl acetate) and 25% grafted ethylene oxide units can be used to prepare capsule cases for drugs which do not require any additional plasticizers (15). 

Sonochemical methods have been used by the Cordoba de Torresi group to prepare Ni(OH)2, Co(OH)2 and mixed Ni/Co hydroxide NPs [33, 34]. For the sonochemical synthesis, the appropriate metal nitrate was mixed with ammonium hydroxide solutions and then sonochemically irradiated for various times. This produced about 5-nm diameter metal-hydroxide NPs that were then immobilized at ITO surfaces using a LbL approach with poly(allylamine) hydrochloride (PAH). In one study, the electrochromic behavior of the LbL deposits was compared with that of bulk deposits... 

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