Ionizing radiation, free-radical graft

Ionizing radiation is unselective and has its effect on the monomer, the polymer, the solvent, and any other substances present in the system. The radiation sensitivity of a substrate is measured in terms of its G value or free radical yield G(R). Since radiation-induced grafting proceeds by generation of free radicals on the polymer as well as on the monomer, the highest graft yield is obtained when the free radical yield for the polymer is much greater than that for the monomer. Hence, the free radical yield plays an important role in grafting process [85]. 

Two important factors in initiating graft copolymerization reactions of vinyl monomers with activated cellulose are (1) the lifetime of the free radical sites and (2) the accessibility of the free radical sites to the monomers. For ceric ion initiation or hydroxyl radical initiation the lifetimes of the free radicals on the cellulose molecule were short (5, 19) therefore, the monomer should be present when the free radicals were formed. For ionizing radiation both short lived and long lived (trapped) free radicals were formed (22, 26, 44). Consequently, the activation reaction and the copolymerization reaction could either be conducted... 

It is important to pay attention to the potential role of peroxides created on the surface of plasma-treated, including plasma polymer-coated, TPOs in the formation of durable bonds between the substrate and primer. It has been known for decades that the peroxides formed on the irradiated polymers (by y-ray. X-ray, electron beams, etc.) can be utilized in graft copolymerization of various monomers. This method is known as the peroxide method of radiation copolymerization [27]. The trunk polymer is first irradiated by ionizing radiation in a vacuum or in an inert gas environment. The irradiated polymer is exposed to air or oxygen to convert free radicals to peroxides. Thus created peroxides-containing polymers were used as the initiator of the free radical polymerization of the second monomer. The polymer peroxides are decomposed by heat or by the use of reduction/oxidation accelerator, i.e., peroxides are converted to free radicals. 

This involves the formation of graft copolymers from a reaction between polymers and monomers. " Monomer units can be propagated onto the polymer backbone to form a graft structure. Free radicals, air, or ionizing radiations are used to initiate the reaction. A... 

Polymer radicals having free radical centers on the backbone chain (to initiate graft copolymerization) can also be produced by irradiation of a polymer-monomer mixture with ionizing radiation. For example, poly(ethylene-grq/i-styrene) can be produced by the irradiation of a monomer-swollen polymer and the initiation reactions can be represented (Odian, 1991) by... 

Mechanistically the processes Involved in grafting styrene in a polar solvent to cellulose with ionizing radiation and sensitized UV are analogous. Each process Is predominantly free radical In nature with a possible contribution from energy transfer processes. In the gamma ray system grafting sites in the cellulose (CelloH) are formed by the sequence of processes shown in Equations 1 to 3 with methanol as representative solvent. 

ABS copolymer is a popular engineering thermoplastic because of its unique properties, which include an excellent mechanical response, chemical resistance, fine surface appearance, and easy processing characteristics. Its unique properties. It consists of a styrene-acrylonitrile (SAN) continuous phase partially grafted onto a dispersed polybutadiene phase of an elastomeric nature. ABS resin is its inherent flammability and lower thermal stability when it is exposed to heat, mechanical stress, and ionizing or ultraviolet radiation in the presence of oxygen because of the formation of reactive intermediates such as free radicals and hydroperoxides. 

Monomers, which polymerize via a free radical mechanism, can be polymerized on the activated support to produce coatings of various thicknesses and depths of penetration. Ionizing radiation has been extensively used for modifying the surfaces of biomaterials via surface grafting reactions. " ... 

Graft copolymerization is the most effective method utilized in the chemical modification of natural fibers. According to Gassan et al. [99], the reaction is initiated by free radicals on the fiber surface. Ionization polymerization of fibers is carried out in an aqueous solution, followed by exposure to a high-energy radiation. Fiber molecule cracks and radicals are subsequently formed. Next, the radical sites of the fiber are treated with a suitable solution compatible with a polymer such as vinyl monomer, acrylonitrile, methyl methacrylate, or polystyrene. Finally, this leads to the formation of a graft copolymer, which possesses fiber and graft polymer characteristics. 

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