Free radical radiation

Living isn t easy, especially at the level of the molecules that make us. Our cells and the molecules they contain are constantly exposed to a hostile environment of viruses, bacteria, free radicals, radiation, and random chemical reactions. We live because our bodies are able to repair themselves from perpetual molecular damage. Over time, however, our bodies lose the ability to self-heal. We age. We grow frail and eventually die. 

Ward JF (1981) Some biochemical consequences of the spatial distribution of ionizing radiation-produced free radicals. Radiat Res 86 185-195 Ward JF (1985) Biochemistry of DNA lesions. Radiat Res 104 103-111... 

Effect of high energy radiation This effect is particularly important in the case of organic solids due to the formation of free radicals. Radiation induced polymerisation is also known. 

Miller JH, Bolger G, Kempner E. Radiation target analysis of enzymes with stable free radicals. Radiat Phys Chem 2001 62 33-38. 

Chem. Descrip. Cyclohexyl vinyl ether CAS 2182-55-0 EINECS/ELINCS 218-561-7 Uses Diluent for cationic, charge transfer, and free radical radiation-curable coatings comonomer in specialty coatings mfg. monomer for tackifying adhesives... 

Chem. Descrip. N-Vinyl-2-caprolactam CAS 2235-00-9 EINECS/ELINCS 218-787-6 Uses Reactive diluent for free radical radiation-curable coatings, inks, and adhesives for flooring, paper, wood, particle board, plastics, textiles, and vinyl... 

Free-radical, radiation-curable systems generally consist of monomers, oligomers, photoactivators, other resins, and fillers or tackifiers. An ultraviolet source or electron-beam generator is used to cure the systems. As an illustration Stueben (37) describes a typical UV-cured PSA system containing acrylates and polyvinyl ether. McGinniss (38) discusses formulation design related to UV-curable systems. The cationic photoinitiators are shown in Fig. 1. 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical (72—74) and radiation-initiated (75) polymerizations are also well known. At a constant temperature, the initial rate of the bulk or solution radical polymerization of acrylic monomers is first order with respect to monomer concentration and one-half order with respect to the initiator concentration. Rate data for polymerization of several common acrylic monomers initiated with 2,2 -azobisisobutyronittile (AIBN) [78-67-1] have been determined and are shown in Table 6. The table also includes heats of polymerization and volume percent shrinkage data. 

Copolymerization is effected by suspension or emulsion techniques under such conditions that tetrafluoroethylene, but not ethylene, may homopolymerize. Bulk polymerization is not commercially feasible, because of heat-transfer limitations and explosion hazard of the comonomer mixture. Polymerizations typically take place below 100°C and 5 MPa (50 atm). Initiators include peroxides, redox systems (10), free-radical sources (11), and ionizing radiation (12). 

The synthesis of the high molecular weight polymer from chlorotrifluoroethylene [79-38-9] has been carried out in bulk (2 >—21 solution (28—30), suspension (31—36), and emulsion (37—41) polymerisation systems using free-radical initiators, uv, and gamma radiation. Emulsion and suspension polymers are more thermally stable than bulk-produced polymers. Polymerisations can be carried out in glass or stainless steel agitated reactors under conditions (pressure 0.34—1.03 MPa (50—150 psi) and temperature 21—53°C) that require no unique equipment. 

Fig. 3. Polymerization initiation and propagation by radiation-generated free radicals. A is the initiating radical produced by irradiating the Hquid coating. (1) represents the Hquid monomer—unsaturated polymer reactive coating system. R is functional. (2) is the growing polymer chain (free radical). The cured...

Radiation Dosimetry. Radioactive materials cause damage to tissue by the deposition of energy via their radioactive emissions. Thus, when they are internally deposited, all emissions are important. When external, only those emissions that are capable of penetrating the outer layer of skin pose an exposure threat. The biological effects of radiation exposure and dose are generally credited to the formation of free radicals in tissue as a result of the ionization produced (17). 

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