On the density of polyethylene single crystals

The density of solution-grown polyethylene crystals was determined by a pycnometer method, judged to be least affected by systematic errors. Values close to the ideal crystallographic density were obtained, the latter having been redetermined on the preparation type in question. This result is consistent with the molecular folds being sharp, no appreciable amount of an amorphous phase being required. Some other methods for measuring densities were found to give results which could be too low. Possibilities of interpreting minor departures from the crystallographic density in terms of details of the crystal morphology are suggested.