Ethylene radiation-induced polymerization

H. Hopff and N. Balint developed a copolymerization process for tetrachloroethylene with ethylene. Radiation-induced chlorination of polyisobutylene is the subject of the chapter of C. Schneider and P. Lopour. M. Litt, V. T. Stannett, and E. Vanzo show that the polymerization of vinyl caproate follows the kinetics of styrene. 

A recent study of the radiation-induced polymerization of nitro-ethylene (38) indicates that the predominant propagating species in this monomer is an anion. This is based on scavenger studies utilizing HBr, substantiated by a study of the electron-trapping capabilities of this monomer in irradiated 2-methyltetrahydrofuran glass (38). 

It has been reported (II, 21) that the presence of mono- and dichloro-ethylene carbonate decreases the yield and molecular weight of PVCA. This can be confirmed for the radiation-induced polymerization when these compounds are present at levels above 1 %. However, as inhibition experiments demonstrated, the inhibition effectiveness of mono- and dichloroethylene carbonate was too small to account for the induction period observed. Furthermore, even after careful separation of these two substances, an unpolymerizable monomer with a chlorine content of about 0.1% was obtained. It should be noted that radiation-initiated polymerization of VCA is especially sensitive to inhibiting impurities, and that the induction period can be easily overrun by using conventional initiators. 

The subjects of reports on radiation-induced polymerization have included the following monomers ethylene,70 tetrafluoroethylene,71 acrylonitrile,72 acrylic acid,78 and methacrylonitrile,74 alkyl acrylates and methacrylates,76 styrene,78 other vinyl monomers,77 78 acrylamide,79 vinylcarbazole,80 maleimide,81 pentenes,82 aminoalkyl monomers,83 isobutyl vinyl ether,84 and buta-1,3-diene.85... 

Radiation-induced curing of plastic coatings has been discussed,8 and radiation-induced polymerization in the solid state reported.87 The radiation chemistry of epoxy-containing electron resists88 and polycondensation induced by ionizing radiation in the urea-formaldehyde system88 have been described. Radiation-induced copolymerization of the following pairs of monomers has been achieved ethylene-hexafluoropropylene,80 tetrafluoroethylene-propylene,81 tetrafluoroethylene-hexafluoropropylene,82 hexafluoroacetone-a-olefins,83 MMA-di- and tri-methacrylates,84 styrene-acrylonitrile,85 buta-1,3-diene-acrylonitrile,88 and acenaphthylene-vinylcarbazole.87... 

The radical polymerization of ethylene, in practice, is initiated by free-radical initiators, although radiation-induced,155 210 photoinduced,211-213 and thermal213,214 initiations are also possible. The temperature of high-pressure polymerization should not exceed 350°C since above this temperature a rapid exothermic (AH = —30.4kcal/mol) thermal decomposition of ethylene can take place leading to a runaway reaction ... 

Experiments using no emulsifier were conducted in tbe same stainless steel autoclave equipment described above (Machi et nf.. 1975). Stable latices were obtained, believed to be achieved by hydroxyl end groups and adsorbed hydroxyl ions. As with a number of the experiments with emulsifiers the polyethylene had a considerable cross-linked gel content. Finally, the same group of workers studied tbe radiation-induced emulsion polymerization of ethylene in a flow system (Kodama et al, 1974). Both potassium inyristate and ammonium perfluorooctanoate were used as emulsifiers. At longer residence times (above 0.2 hr) the rate of polymerization was essentially constant. As with the batch system it was assumed that the number of particles remained constant. In this region the rate was found to be proportional to tbe 0.3 power of the potassium myristate concentration and the 0.5 power of the dose rate, not too different from the batch systems. The kinetics was developed and estimates of tbe propagation rate constants obtained. Despite other similarities between the two systems, these were quite different, however, from those extracted from the batch experiment. 

Surface Effect. As seen before, 5 A. molecular sieves (LMS) increase considerably the yield of radiation induced ethylene polymerization. 

Most authors of the high-pressure studies also report tertiary and higher-order ions, and sequences of consecutive reactions leading to these higher-order ions are proposed. Such sequences are important in the radiation induced ionic polymerization of ethylene. Here, however, we will not discuss all of them but simply mention one important debate on whether or not intermediate complexes participate in the polymerization sequence. 

Ethylene (Et) and chlorotrifluoroethylene (CTFE) have been copolymerized (ECTFE) in aqueous and nonaqueous mediums. Aqueously, polymerization can be initiated by oxygen-activated triethylboron at low temperatures, by peroxides, and by radiation induced techniques. The earliest record of ECTFE polymeriza-... 

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. 

Heterogeneous Ethylene Polymerization Induced by Radiation Influence of the Catalyst Amount... 

FTIR spectra are also benehcial in establishing the optimum conditions for curing acrylic adhesives by exposure to UV radiation. The degree of UV polymerization of acrylic adhesives can be followed by the decay of the ethylenic ( CH=CH2) absorption band at 810 cm. Scherzer et al. studied the UV-induced crossUnking of a pressure-sensitive acrylic resin with copolymerized benzophenone groups using variable UV doses and intensities. Real time FTIR spectroscopy was also used to study the effect of various photoinitiators in accelerating the photopolymerization of acrylate resins. ... 

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