Radiation-initiated graft polymerization

This preliminary study has shown that radiation initiated graft polymerization and co-polymerizatlon on a polyolefin film surface can be achieved using the above described process with electron initiation. This process can be employed with a wide range of monomers. ... 

Other polymerization methods such as coordination polymerization," " surface electro-initiated emulsion polymerization," radiation-induced graft polymerization (RIGP)," surface thiol-lactam-initiated radical polymerization (TLIRP)" and LbL click grafting" have been employed to graft polymers from CNT surfaces. 

The quantitative effect of diffusion control on the rate of radiation-initiated graft polymerization has been studied theoretically for systems in which the diffusion-free reaction may show various dependences of rate on the concentration of monomer other than the usual first-order dependence. The study is very general and could be applied to systems involving a variety of modes of initiation and termination. 

The effects of diffusion control on the rate of radiation-initiated graft polymerization of cellulose have been studied theoretically. The effects of such variables as the initiator concentration, temperature, and monomer polymer ratio on the graft copolymerization of acrylamide and 0-methylcellulose have been investigated. The thermal properties and behaviour of graft copolymers of formaldehyde-cross-linked 0-cyanoethylcellulose and acrylates have been studied. Copolymerization of periodate-oxidized cellulose (aldehydocellulose) with glycidyl methacrylate in the presence of an enzyme e. peroxidase) afforded a means of immobilizing the enzyme without loss of activity. ... 

The creation of active sites as well as the graft polymerization of monomers may be carried out by using radiation procedures or free-radical initiators. This review is not devoted to the consideration of polymerization mechanisms on the surfaces of porous solids. Such information is presented in a number of excellent reviews [66-68]. However, it is necessary to focus attention on those peculiarities of polymerization that result in the formation of chromatographic sorbents. In spite of numerous publications devoted to problems of composite materials produced by means of polymerization techniques, articles concerning chromatographic sorbents are scarce. As mentioned above, there are two principle processes of sorbent preparation by graft polymerization radiation-induced polymerization or polymerization by radical initiators. We will also pay attention to advantages and deficiencies of the methods. 

The theory of radiation-induced grafting has received extensive treatment [21,131,132]. The typical steps involved in free-radical polymerization are also applicable to graft polymerization including initiation, propagation, and chain transfer [133]. However, the complicating role of diffusion prevents any simple correlation of individual rate constants to the overall reaction rates. Changes in temperamre, for example, increase the rate of monomer diffusion and monomer... 

Polymer radicals can also be produced by the irradiation of a polymer-monomer mixture with ionizing radiation. Thus, the interaction of ionizing radiation with polyethylene-styrene produces radical centers on polyethylene, and these initiate graft polymerization of styrene to produce poly(ethylene-gra/i-styrene) [Rabie and Odian, 1977]. 

Grafting of Vinyl Monomer on Radiation-Peroxidized Polymer. The polymer is irradiated in the presence of air or oxygen and then immersed in monomer. The peroxides in the irradiated polymer are decomposed by heat or catalysts to form free radicals, capable of initiating graft polymerization. 

Usually, free-radical initiators such as azo compounds or peroxides are used to initiate the polymerization of acrylic monomers. Photochemical and radiation-initiated polymerizations are also well known. Methods of radical polymerization include bulk, solution, emulsion, suspension, graft copolymerization, radiation-induced, and ionic with emulsion being the most important. 

The butadiene and butadiene-acrylic monomer systems polymerize when irradiated on PVC or vinyl chloride copolymer latex. The structure of the polymer obtained may be grafted if it can be proved that the copolymer properties are different from the blend properties. To elucidate the structure we studied a copolymer obtained by polymerizing butadiene-acrylonitrile on a PVC homopolymer lattice. Owing to practical reasons and to exclude the secondary effect of catalytic residues we used y radiation. However, we shall observe in a particular case the properties of peroxide-initiated graft copolymer. 

NABLO, SAM V. RANGWALLA, IM J. WYMAN, JOHN E. Electron-Initiated Graft Modification of Polyolefins. Radiation Curing of Polymeric Materials, ACS Symposium Series 417, American Chemical Society, Washington, DC (1990) 534-551. 

An interesting conclusion can be derived from the fact that radiation initiates cationic grafting of isobutylene. Since chain transfer is usually small in such systems, it seems pertinent to assume that the reaction is initiated by a polymeric ion and moreover that this ion attaches itself... 

Polyvinylpyrrolidone (PVNP) Grafting. PVNP was grafted onto Biomer by radiation copolymerization of N -vinylpyrollidone monomer (Polysciences, Inc.) onto the elastomer surface. Polymerization was ultraviolet radiation-initiated in a monomer solution containing 0.1% azobisisobutyronitrile (AIBN) (Polysciences, Inc.). 

It Is known that most radiation Initiated polymerization processes are Initiated by Che free radicals created by radlolysls of Che monomers. If a monomer or a mixture of monomers Is Irradiated In Che presence of a polymer, a graft copolymer Is formed which has different physical properties. For example. If a second polymer like polyacrylonitrile or polyvlnylldlne chloride, which possess superior barrier properties against permeation by oxygen, carbon dioxide, water vapor etc.. Is grafted to a polyolefin film like polyethylene, polypropylene, etc., the barrier properties of the composite film are greatly enhanced compared with Che polyolefin film. 

For example, compositions of 10 ml of a 3.75 gm per 100 ml aqueous solution of sodium dioctylsulfosuccinate (Aerosol OT or Manoxol OT) and 1.25 ml of vinyl acetate with small additions of sodium dihydrogen phosphate, after exclusion of oxygen by at least four degassings, were sealed in glass ampoules. The samples were exposed, at 15°C, to a Co source (100 curie). Conversion was nearly 75% after 30 min. Polymers of MW as high as 10 were formed. The polymers contained trapped free radicals capable of initiating graft polymerization with methyl methacrylate after removal from the radiation source [185]. 

Considerable work has been done on the initiation of the vinyl fluoride by ionizing radiation much as y-radiation from a °Co source. A selection of references on this research includes Usmanov and other authors [4,48-62], Of these, Usmanov et al. [4] deal with the graft copolymerization of vinyl fluoride to some natural and synthetic polymers. Usmanov et al. [53] discuss the formation of branched polymers during radiation-induced polymerization. Gubareva et al. [54] deal with solution polymerizations. Nakamura et al. [58, 59, 61] deal with emulsion polymerizations of vinyl fluoride by radiation initiations. Usmanov et al. [60,61] discuss the effects of chain-transfer agents during radiation-initiated polymerization. Some copolymerization studies are described in Usmanov et al. [55]. 

Also within this category of application is the field of radiation grafting onto pre-existing polymeric substrates. E-beam or gamma sources can be used to initiate grafting onto a range of materials, for example poly(olefin)s, fluoropolymers, and cellulosics. The biocompatibility of poly(olefin)s can be greatly... 

Other methods of generating free radicals can also be used to initiate graft polymerization with elastomers, both natural and synthetic. These include irradiation of polymer-monomer mixtures by ultraviolet light (Cooper et al., 1959), high-energy radiation (Cockbain et al., 1959 Gupta and Anjum, 2003), and mechanical shear. The latter is of particular interest because of its unique mechanism, and has been extensively investigated. ... 

Radiation-induced grafting is a process where, in a first step, an active site is created in the preexisting polymer. This site is usually a free radical, where the polymer chain behaves like a macroradical. This may subsequently initiate the polymerization of a monomer, leading to the formation of a graft copolymer structure where the backbone is represented by the polymer being modified, and the side chains are formed from the monomer (Fig. 1). This method offers the promise of polymerization of monomers that are difficult to polymerize by conventional methods without residues of initiators and catalysts. Moreover, polymerization can be carried out even at low temperatures, unlike polymerization with catalysts and initiators. Another interesting as-... 

Free radicals are produced by the dissociation of excited molecules. High-energy-irradiation-induced polymerization is especially important for graft polymerization and polymerization in the solid state. Because of high investment costs, high-energy-radiation-initiated polymerization of gaseous, liquid, or dissolved monomers has not become established. However, to a small extent ( 2000 t/a), the polymerization of methyl methacrylate is radiation initiated. 

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