Showing papers on "Plastomer published in 1959"

γ-Irradiation of rubber and styrene. Graft polymer formation

Abstract: Styrene, styrene mixed with rubber, and rubber alone have been exposed to gamma radiation from Co-60. The G value for polymerization-initiating radicals formed from rubber in the mixtare, G(i.r.) = 0.26, has been calculated from corresponding values obtained by estimation of the number of polystyrene molecules formed in styrene and in the mixture. A G (radical) value for rubber when irradiated alone, G(r), has been assessed from a G (crosslinking) value, G(X), which was determlned under closely similar experimental conditions, as G(r) = 2G(X) ~ 6. The large discrepancy between G(r) and G(i.r.) cannot be explained satisfactorily on the supposition that radicals formed from rubber have a low efficiency in initiating the polymerization of styrene. Therefore, it is argued that the G(r) value itself is lower in the mixture. Evidence for this argument is provided by the lower rate of gelling in the mixture. This protection of rubber by energy transfer to styrene is an important example since in only one previous case has experimental evidence been provided to exclude an alternative radical mechanism. By polymerization in the presence of crosslinked rubber, uncombined polystyrene could be readily partitioned into the sol fraction by equilibration of the gross polymer in benzene.more » About 15% of the polystyrene was free. Hexachloroethane was chosen as an example of an additive with a high G (radical) value. As would be expected, it increases the rate of polymerization but does not lead to a correspondingly large amount of free polystyrene (about 23%). Graft polymer formation from styrene and methyl methacrylate is compared and attention is drawn to the importance of the formation and subsequent reactions of initially nonpolymeric radicals in determining the proportion of free plastomer. (auth)« less