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Frarw-Vinylene

A second important reaction observed in irradiated polyethylene and certain other polymers as well as paraffins is the formation of trans-vinylene. This product is far less influenced by such factors as temperature or radical scavengers than is crosslinking, and it is therefore often assumed to be formed directly by a molecular process—i.e., molecular detachment of hydrogen. Even this simple explanation cannot be fully sustained. Long after radiation has ceased, the frarw-vinylene concentration continues to rise or fall, whether the specimen is exposed to oxygen or not. This behavior may possibly be correlated with the reaction of trapped alkyl and allylic radicals, which, being slightly mobile, can add to frarw-vinylene or each other over a period of days. [Pg.16]

Apart from this behavior, the concentration of frarw-vinylene increases with dose, at first linearly but then tends to a limiting value which depends on the type of radiation (7). This limit is possibly caused by the capture by frarw-vinylene of the thermalized hydrogen atoms released elsewhere by radiation. From the limiting concentration of unsaturation the number of collisions made by each thermalized hydrogen atom before it abstracts can be deduced this lies in the range 103 to 104. [Pg.16]

To obtain the absorbances at 910 and 967 cm. 1, it was necessary to correct the observed band intensities for the overlapping of adjacent bands. The band at 910 cm."1 for the vinyl group was corrected for the absorbance from the wing of the 967-cm."1 frarw-vinylene band,. and the latter band was corrected for the vinyl band at 995 cm. 1. The Lorentz band shape equation was used to calculate the absorbance in the wings, and in the thicker specimens, successive approximations were necessary. This treatment gave the four equations below, which yielded the concentrations of trans and vinyl groups for the emulsion and sodium polybutadienes listed in Table I. Implicit in these equations is the assumption that the absorptivities are independent of concentration. [Pg.72]


See also in sourсe #XX -- [ Pg.47 , Pg.61 ]




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