The polymerization of ethylene sensitized by the thermal decomposition of ethyl iodide in the presence of mercury vapor has been studied a t 250°, 275", and 300°C. C14-labelled ethyl iodide was used in a number of experiments. The increase in the rate of decomposition of ethyl iodide in the presence of ethylene and the formation of butyl iodide are accounted for by equilibrium processes of the type R I f H g = R f H g I . 'The important features of the reaction were established from the identity, quantity, and activity of the various products. The predominant formation of olefins is attributed to the isomerization and decomposition of large radicals. Very little of the butane is formed by the combination of ethyl radicals. Radical disproportionation is the most important chain termination step.The decompositioil of the lower allcyl iodides has been studied exteilsively (10) and it is generally agreed that in both the thermal reaction and in the photolysis in the region of the contiiluum (ca. 2600 A) the primary process consists in the formation of alkyl radicals and iodine atoms. The quantum yields of the photochemical process are low because of the baclc reaction but can be greatly increased by trapping the iodine atoms with mercury or silver. The thermal or photochemical decompositioil of alkyl iodides in the presence of ethylene and either mercury or silver should therefore afford a conveilieilt method for studying the free radical sensitized polymerizatioil of ethylene.Juilgers and Yeddailapalli (5) have studied the polymerizatioil of ethylene sensitized by the photolysis of methyl, ethyl, ?z-propyl, and isopropyl iodides in the presence of mercury a t temperatures in the range 130' to 275OC. Under conditions lilcely to yield low radical concentrations, viz. low iodide concentrations, high ethylene concentrations, and low light intensities, they found that the "yield", defined as the ultimate pressure decrease on prolonged irradiation divided by the initial pressure of iodide, reached maximum values which were in the approximate ratio 3.5 : 3.0 : 2.5 for methyl, ethyl, and the propyl iodides, respectively. They concluded from this that the final polymer had approximately the same molecular weight in each case and that for steric reasons the growing radicals formed by the successive addition of ethylene molecules uilderwerlt chain termination when they reached a more or less common critical size. According to their mechanism all the products should be saturated, for a t low radical concentrations they assumed that chain termination would take place by the reactions while a t high radical concentrations they assumed t h a t it would occur by '~Manuscripl received September 82, 1955.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.