Abstract
The determinations of ethylenic unsaturation were made by the infrared method on the fractions of the typical commercial high pressure polyethylenes which were fractionated with respect to molecular weight. On the tubular-type polyethylenes, the amount of ethylenic unsaturation decreased with increasing molecular weight, while on the vessel-type polyethylenes their molecular weight dependencies were comparatively small. These results correspond to the distributions of short-chain branching and these are reasonable results in view of the Oaks-Richards mechanism on the formation of unsaturation.
Some of these samples showed very broad distribution of unsaturation and this was considered to be caused by the formation of vinyl or vinylidene groups resulted from a chain transfer reaction to propylene or isobutene. This consideration was supported by the fact that for these samples the numbers of unsaturation per molecule in each fractions were nearly equal and the ratio of the number of butyl branch per total number of branch was lower than that of ordinary samples presumably because of an increase of methyl branch resulted from copolymerization with propylene or isobutene.
