Experiments on the location of chain ends in monolayer single crystals of polyethylene

The location of vinyl end groups in monolayer polyethylene crystals (specially prepared to have surfaces highly accessible to gaseous reactants) has been investigated by exposing the crystals to ozone and determining the extent of reaction by infrared spectroscopy. It was found that, for the type of crystals used, about nine-tenths of the chain ends reacted very rapidly and it is deduced that these are excluded from the crystal lattice and should lie on the crystal surfaces. The remaining fraction of ends were, by comparison, highly resistant to oxidation.

The consequences of this deduction are discussed; it is suggested that the chain segment ejected together with the chain ends could account for a large part of the amorphous content associated with this type of crystal. In addition, the results imply that the crystal lattice is inaccessible to ozone even when it contains defects such as those caused by end groups, which is of consequence for work on oxidative degradation both for its own sake and in aid of morphological studies.