Radiation emulsion polymerization

The efficiency of radiation emulsion polymerization is much higher than that for polymerization in bulk or in suspension conversion and the molecular weight of the polymer increase by one to two orders of magnitude. This increase results from the formation of additional radicals in water (increase in Gr) and a decrease in the termination rate. 

Hence, in order to ensure a relatively high rate of radiation-induced polymerization in the emulsion, low dose rates (0.1-1 Gy/s) and low absorbed doses are required. For all these reasons, radiation emulsion polymerization is particularly advantageous from an economical standpoint. Its activation energy, just as for other processes of radical radiation-induced polymerization, is 15-35 kJ/mol. The molecular weight of polymers increases with temperature, as in the case of typical free-radical processes (to a certain extent). This increase is due to an increase in kp with temperature, whereas k, does not depend on the temperature. 

Apart from the advantages of radiation emulsion polymerization indicated above and those characteristic of radiation-induced polymerization in general, the following advantages should also be mentioned. 

Polyacrylonitrile synthesized by radiation emulsion polymerization is used for manufacturing high tenacity fibres. 

There was some indication that oxygen play an important role in inhibiting the rate of polymerization as reported from radiation emulsion polymerization of n-BA, glycidyl methacrylate and methacrylic acid ). Conversion was found to be much lower if during the irradiation the emulsion still be stirred without the flowing of an inert gas such as N. ... 

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

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. 

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. 

Seguchi T, Suwa T, Tamura N, Takehisa M (1974) Morphology of polytetrafluoroethylene prepared by radiation-induced emulsion polymerization. J Polym Sci Polym Phys Ed 12 2567... 

Radiation Induced Emulsion Polymerization of Vinyl Chloride... 

The emulsion polymerizations were carried out in vacuum sealed ampoules in a rotating wheel device positioned in the gamma field, providing agitation and assuring radiation uniformity by tumbling the ampoules end over end. The equipment used has been described previously (10). 

Molecular Weight of Polyvinyl Chloride Produced by Radiation Induced Emulsion Polymerization at 25°C... 

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. 

Figure 11. Solutions of the Smith-Ewart recursion equation for the case of no aqueom propagation or termination. Dotted line m = 0 (Smith-Ewart Case II). Curve 1 (m = 10 ) depicts typical styrene-like polymerization. Curve 2(m = 0.01) depicts radiation initiated emulsion polymerization of vinyl chloride. Curve 3 (m > 1.0) depicts chemically initiated emulsion polymerization of vinyl chloride.

In general, for most investigations, y radiation has been used because of its high degree of penetration and the ccanparative ense of estimating dose-depth characteristics and because radical fluxes comparable to those used with chemical initiation can easily be achieved- There have also been a few, comparatively brief, studies using electron accelerators to initiate emulsion polymerization in emulsion. These have mainly been conducted in Japanese laboratories. 

From a fundamental point of view it is interesting to speculate on tbe differences that could exist between the kinetics of emulsion polymerization initiated by y radiation and those of a conventional chemical initiator with, for example, potassium persulfate. At dose rates jiving a free radical flux comparable to those achieved with chemical initiation any differences... 

Recently, Garreau et al. (1979) reported a careful and rather detailed study of the kinetics of the radiation-induced polymerization of styrene in emulsion with sodium lauryl sulfate under conditions found earlier to lend to close agreement with simple Case 2 Smilh-Ewart kinetics (Smith, 1948). Most of the normal reaction variables were studied, and the rates of polymerization were found to be independent of the luonomer-to-water... 

Acres and Dalton (1963a) also studied the emulsion polymerization of methyl methacrylate initiated by Co y radiation using a recording dilatometer. Only the conversion-time curves were measured with constant dose rate, varying monomer concentration, and with constant monomer concentration at different dose rates. Except at the lowest monomer concentration a clear gel effect was observed, with linear rates up to that point. The linenr rates increased with increasing monomer concentration up to about 0.4 mol/liter and then leveled oif. The dependence of the rate, before the gel effect, on the dose rate was 0.4 and, unlike their findings with styrene, not dependent on the monomer concentration. Their results were consistent with those of Hummel ei al. that methyl methacrylate follows, with y radiation, the generally accepted Smith-Ewart Case 2 kinetics except for the marked gd effect. 

Hoigne and O Neil (1972) studied several features of the y radiation-initialed polymerization in emulsion. Sodium lauryl sulfate, dioctyl and dibutyl sodium sulfosuccinates, and two nonionic, polyoxyethylene-type emulsifiers were used. Sodium lauryl sulfate gave, by far, the hipest rates and most stable lattices and was used for all of the results reported. The rates were found to be 0.43 order on the dose rate and 0.53 on the... 

Wang (1962) was the first to report studies on the y-radiation initiated polymerization of vinyl chloride in emulsion at room temperature. Rapid rates to high conversions were obtained after rather long induction periods of 1 to 3 hr. The degrees of polymerization were constant within experimental error at about 2000, in keeping with termination being dominated by chain transfer to monomer. Little or no dependence of the rale on the emulsifier concentration or the monomer concentration was observed. However, tbe rates were proportional to the 1.22 power of the dose rate. 

Panajkar and Rao (1979) have reported a ratber extensive study of the y radiation-initiated polymerization of vinylidene chloride in emulsion. With sodium lauryl sulfate as the emulsifier smooth polymerization-time curves at high rates were obtained, up to more than 9 conversion. Between 45 and 60% conversion, the linear region, the rate was 0.3 order with respect to tbe emulsifier concentration. The molecular weights were found to increase with conversion and values up to 79,000 were obtained. Some reasons for the departure from Smith Ewart behavior were suggested. Earlier. Hummel el al. (1967) had presented some interesting data on a closely related system, a similar rate-time behavior was observed and a tentative explanation proposed. Both discussions were based on tbe insolubility of the polymer in its own monomer. 

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