Polymerization gamma radiation

The reported values for the exponent of the dose-rate for the polymerization rate in gamma radiation-induced copolymerization of acrylamide with methyl chloride salt of A, A -dimethylaminoethyl methacrylate (DMAEM-MC) in aqueous solution was found to be 0.8 [16]. However, the dose-rate exponent of the polymerization rate at a lower dose-rate was found to be slightly higher than 0.5 for gamma radiation-induced polymerization of acrylamide in aqueous solution [45,62]. 

Precipitation polymerizations dominated the early work which aimed at preparing industrially important hydrocarbon polymers in C02. In 1968, Hagiwara and coworkers explored the polymerization of ethylene in C02 using both gamma radiation and AIBN as free radical initiators [79]. Reactions were conducted at pressures of 440 bar and over the temperature range of 20-45 °C. 

In dispersion polymerization, the monomer and initiator are dissolved in the continuous phase, which acts as a nonsolvent for the developing polymer. The continuous phase can be organic, aqueous, or a mixture of miscible phases. Two methods of initiation have been employed, including gamma radiation [75] and chemical initiation by potassium perox-odisulphate [76]. As the polymer is formed, it precipitates as nanoparticles. These particles are not polymeric precipitates as in precipitation polymerization. Rather, they are swollen by a mixture of the monomer and the continuous phase [39],... 

Kreuter and Speiser [77] developed a dispersion polymerization producing adjuvant nanospheres of polymethylmethacrylate) (PMMA). The monomer is dissolved in phosphate buffered saline and initiated by gamma radiation in the presence and absence of influenza virions. These systems showed enhanced adjuvant effect over aluminum hydroxide and prolonged antibody response. PMMA particles could be distinguished by TEM studies and the particle size was reported elsewhere to be 130 nm by photon correlation spectroscopy [75], The particle size could be reduced, producing monodisperse particles by inclusion of protective colloids, such as proteins or casein [40], Poly(methylmethacrylate) nanoparticles are also prepared... 

Bulk polymerization of acrylonitrile initiated by gamma radiation was described by Chapiro at The process is greatly complicated by other reactions. Occlusion of... 

Gamma radiation-induced mass and emulsion polymerization of vinyl monomers has been studied by the American, Metz, and the German, Hummel. 

Gamma-Radiation-Induced Polymerization of Some Vinyl Monomers in Emulsion Systems... 

The goal of our work was to study the gamma-radiation-induced emulsion polymerization of some less common vinyl monomers, and to obtain more reliable data by refining the experimental technique. 

Polymerization of monomer-impregnated concrete was initially carried out with 60Co gamma radiation. A principal advantage of using radiation is that free radical chain reactions can be induced at ambient temperature. This limits vaporization loss and may produce a better concrete-polymer bond. The disadvantages are the dose requirements and the relatively high initial investment required for the radiation source and facility. 

Some typical 60Co gamma radiation dose requirements for fully polymerizing several concrete-polymer systems are given in Table II. There is some evidence (5) that a lower dose is required to polymerize monomer in concrete than monomer alone. This may be attributed to energy transfer effects in the heterogeneous concrete-monomer system. 

Kent, J. A., Winston, A., and Boyle, W. R., "Preparation of Wood - Plastic Combinations using Gamma Radiation to Induce Polymerization", U. S. Atomic Energy Commission Report 0. R. 0. - 600 and 612 (1962). 

This discussion is not intended to be an exhaustive review of the wood-polymer literature, but rather an overview of the processing procedures used today. In general, the free radicals used for the polymerization reaction come from two sources, temperature sensitive catalysts and Cobalt-60 gamma radiation. In each case a free radical is generated by the process, but from that point the vinyl polymerization mechanism is the same. Each... 

Since the cell wall structure of the wood is not swollen by the vinyl monomer, there is little opportunity for the monomer to reach the free radical sites generated by the gamma radiation on the cellulose to form a vinyl polymer branch. From this short discussion, it is reasonable to conjecture that there should be little if any difference in the physical properties of catalyst-heat initiated or gamma radiation initiated in situ polymerization of vinyl monomers in wood. 

Many different vinyl monomers (9) have been used to make wood-polymers during the past ten years, but methyl methacrylate (MMA) appears to be the preferred monomer for both the catalyst-heat and radiation processes. In fact, MMA is the only monomer that can be economically polymerized with gamma radiation. On the other hand, all types of liquid vinyl monomers can be polymerized with Vazo or peroxide catalysts. In many countries styrene and styrene-MMA mixtures are used with the Vazo or peroxide catalysts. 

The polymerization of vinyl monomers is an exothermic reaction and a considerable amount of heat is released, about 18 kCal per mole. In both the catalyst-heat and gamma radiation processes the heat released during polymerization is the same for a given amount of monomer. The rate at which the heat is released is controlled by the rate at which the free radical initiating species is supplied and the rate at which the chains are growing. As pointed out above, the Vazo and peroxides are temperature dependent and the rate of decomposition, and thus the supply of free radicals, increases rapidly with an increase in temperature. Since wood is an insulator due to its cellular structure, heat flow into and out of the wood-monomer-polymer material is restricted. In the case of the catalyst-heat process heat must be introduced into the wood-monomer to start the polymerization, but once the exothermic reaction begins the heat flow is reversed. 

A more detailed study has been made of the effect of temperature on the free radical polymerization of methyl methacrylate (33). Polymers were prepared at —78° and at 0° using Co80 gamma radiation and at 50° and 100° using benzoyl peroxide initiator. In Table 6 are summarized the structures of these polymers. A trend toward increasing syndiotactic character with decreasing temperature is clearly evident. 

The styrene copolymers were prepared by bulk polymerization at 100°, using benzoyl peroxide as initiator. Methyl methacrylate styrene mole ratios in the feed were 10 90, 25 75, 50 50, 75 25, and 90 10. Conversions varied from 4.5 to 8.1%. Methyl methacrylate a-methyl-styrene copolymers were prepared using benzoyl peroxide at lower a-methylstyrene ratios and U.V. or Co60 gamma radiation to initiate copolymerization at the highest a-methylstyrene ratios, in which reaction is very slow. The mole ratios in the monomer feed were 12 88, 28 72, 54 46, 78 22, and 91.5 8.5. 

As in the case of many other polymeric materials, ionizing radiation electron beam, or EB, and gamma radiation has a variety of effects on fluoropolymers. It may... 

The emulsion polymerization of vinyl chloride, initiated by gamma radiation from a Cobalt-60 source, has been studied in detail. Good conversions to high yields were obtained. 

A recent study by Mechelynck-David 11, 12) on ethylene polymerization induced by Co ° gamma radiation, has pointed out the influence of the presence of various solids upon the course of the reaction. 

Simple hydrogen-bonded acetylenes such as propioltunide (5) and propiolaldehyde semicarbazone (6), whose crystal structures reveal short contacts between acetylenic ctubons, are unreactive to gamma radiation when the crystals are grown by vacuum sublimation (21). Polymerization of these compounds proceeds to a low degree of conversion for crystals grovm in chlorinated solvents. 

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