Radiation monomers, gamma

The reported values for the exponent of the monomer concentration for the rate of polymerization were found to be 1.26[61], 1.3[16] for gamma radiation-induced copolymerization of acrylamide with N,N-di-ethyldiallylammonium chloride and methyl chloride salt of /V,N-dimethylaminoethyl methacrylate (DMAEM-MC). Ishigue and Hamielec [34] have shown that the... 

Alternatively, the film is placed between two perforated lead plates and grafted with monomer M by the mutual method. After grafting, the film is now placed between the two perforated lead plates taking precautions that only the ungrafted portions of the grafted film are exposed to gamma radiations in the presence of monomer M2. Schematically, the preparation of the mosaic membrane is shown in Fig. 2. 

There are a number of important factors that must be considered before applying gamma radiation-induced grafting. These factors include the radiation sensitivity of the polymer/monomer system, radiation dose and dose rate, type and concentration of inhibitor, type of solvent or diluent, and monomer concentration. The effect of such parameters on the grafting efficiency during mutual grafting is given below. 

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... 

Radiolysis Effects. Radicals formed in solvent (SH) and trunk polymers (PH) are important in the grafting of monomers (MH) with gamma radiation. With polymers such as polyethylene, grafting sites are formed by direct bond rupture (Equation 1). Additional sites are also... 

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. 

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. 

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. 

Gamma radiation is the most convenient type of high-energy radiation for initiating polymerization because its high penetrating power affords uniform irradiation of the system. Because gamma rays are absorbed to the same extent by solids as by liquids, solid monomers can be polymerized readily. This allows polymerization of many monomers at low temperatures. 

The structure of itaconic acid bears some resemblance to methacryllc acid. While It Is know that methacryllc acid and methacrylic anhydride do enhance sensitivity when copolymerized with methyl methacrylate, some of the Increase In speed may be due to porosity (7,12). The gas formation may cause a higher rate of dissolution then can be attributed to chain scission alone. Pittman and co-workers have reported G(s) values for poly(methacryllc anhydride) of 0.4 (10) and 1.8 and 2.9 (14) based on gamma radiation experiments. Hiroaka (12) measured G(s) by gas evolution on Irradiation of films with electron beams and established values In the ration 1 2 6 for the methyl methacrylate. A terpolymer with the three components In the molar ratio of 70 15 15 (same three monomers) was selected by Moreau et al (13) on the basis of complete lithographic evaluation. The speed Is 4 to lOx that of PMMA. As aforementioned, an Increase In G(s) may be only partially responsible. 

CAPUTO G., GALIA F., SCRO F., SPADARO G., FILARDO G., Gamma radiation induced polymerization of vinyl monomers in dense CO2. Radiat. Phys. Chem., (2002), 63,45-51. 

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