Crosslinking ionizing radiation

Elastin-mimetic protein polymers have been fabricated into elastic networks primarily via y-radiation-induced, radical crosslinking of the material in the coacervate state [10]. Although effective, this method cannot produce polymers gels of defined molecular architecture, i.e., specific crosslink position and density, due to the lack of chemoselectivity in radical reactions. In addition, the ionizing radiation employed in this technique can cause material damage, and the reproducibility of specimen preparations may vary between different batches of material. In contrast, the e-amino groups of the lysine residues in polymers based on Lys-25 can be chemically crosslinked under controllable conditions into synthetic protein networks (vide infra). Elastic networks based on Lys-25 should contain crosslinks at well-defined position and density, determined by the sequence of the repeat, in the limit of complete substitution of the amino groups. 

PVDF has not been investigated as a resist due to poor solubility, but it is known to predominantly crosslink when irradiated by ionizing radiation like PMFA. (8) The etch resistances of PVDF and PMFA are most certainly governed by the strong C-F side chain bond(s). 

The effects of ionizing radiation on a low and a high density polyethylene and an ionomer indicate that similar networks are formed in the ionomer and in the low density polyethylene. The former crosslinks about 1.5 times as readily as the latter. In the high density resin, the network characteristics, and hence, presumably, the type and distribution of links, differ considerably from those in the other two resins. As a result, crosslinking rates in the high and low density polyethylenes cannot be directly compared. 

Radiation-Induced Crosslinking. In the absence of oxygen, the predominant effect of ionizing radiation on UHMWPE is crosslinking (27). Crosslinking of UHMWPE forms covalent bonds between the polymer chains, which inhibit cold flow or creep of the individual polymer chains. 

Microwave Supported Crosslinking. Because of abrasion in conventional UHMWPE, the body may react with inflammations and tissue alterations. The mechanical properties can be improved by additional crosslinking. Crosslinking is customarily achieved by way of intermediate stages involving radicals that are produced either by means of ionizing radiation or, by chemical processes. 

Highly crosslinked UHMWPE can be produced by irradiation of a blank UHMWPE with ionizing radiation, in particular by X-rays, y-rays or electron beams, in order to produce radicals. The subsequent treatment of the irradiated material consists in exciting free radicals, which have not recombined, by means of microwave radiation or ultrasound. The process is claimed to ensure a substantially complete recombination of the free radicals. In addition, the crosslinking of the UHMWPE is also further optimized (30). 

Distel L, Distel B, Schussler H (2002) Formation of DNA double-strand breaks and DNA-protein crosslinks by irradiation of DNA in the presence of a protein. Radiat Phys Chem 65 141-129 Dizdaroglu M (1986) Chemical characterization of ionizing radiation-induced damage to DNA. Bio Techniques 4 536-546... 

Polyethylene is known as one of the typical polymers which crosslink under the influence of ionizing radiation. The radiation-induced crosslinking (the formation of C-C covalent bonds between polymer chains) of polyethylene has long attracted the interest of a large number of research workers, because this polymer has the most simple chemical structure for the fundamental study of radiation effects on polymers, and also because the irradiation with ionizing radiation is a practically important means of modifying the mechanical and thermal properties of polyethylene. 

Irradiated Polystyrene. The irradiation-induced crosslinking of expandable polystyrene with ionizing radiation in the range of 200-300 megarep raises the serviceability temperature of the foam in proportion... 

The formation of keto-phosphonate structure within macromolecule leads to the removal of internal unsaturation. Triallyl cyanurate and ionizing irradiations [210] made a E-P block copolymer-PE blend thermally stable. Triallyl cyanurate increases the crosslinking density probably due to addition reactions between polymeric and allyl radicals produced by ionizing radiation. The addition of 2,2,4-trimethyl-l,2-di-hydroquinoline and bis[4(l-methyl-1-phenylethyl)pheny 1]-amine stabilized a PE-EPDM blend against heat [211]. Popov et al. [212] studied the ozone effect on PE-iPP blend. The oxidation rate was detected in relation to... 

One of the most interesting problems was evaluation of quantum yield for light induced crosslinking of poly(vinyl butyral) in the presence of diphenyl sulphoxide. Mathematical treatment of the molecular changes produced in polymers by light is based on that by ionizing radiation. In our case, as the changes above the gel point were examined, the only suitable approach... 

Figure 2 DNA damage induced by ionizing radiation. A) DNA damage and repair. All the constitutive elements of DNA (sugar-phosphate backbone and bases) are possibly modified by ionizing radiation. Single strand breaks (SSB), oxidized bases and abasic site are processed by base excision repair (BER), double strand breaks (DSB) by homologous recombination and non homologous end joining (HR and NHEJ) and DNA-protein crosslinks by nucleotide excision repair (NER). B) Quantitative measurement of radiation-induced and spontaneous DNA damage.

Copolymers of 2,3-epoxypropyl methacrylate and butadiene prepared by solution free radical polymerization were tested as potential candidates for electrom negative resists.The sensitivity of the copolymers to ionizing radiation was determined with a linear accelerator.The experimental data were treated according to the Saito-Inokuti statistical theory.The calculated crosslinking yield values, G(x),were dependent an... 

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