Density of polyethylene crystals grown from solution

The density of Marlex 50 polyethylene crystals grown from a 0.75 percent solution in p-xylene at 70 °C was measured by a pycnometric method. Difficulties in making the measurements to the necessary accuracy are discussed. The values obtained were close to 0.98 g/cm³ at 30 °C and significantly less than the crystallographic density of 1.00 g/cm³. Several possible explanations of this density deficiency are mentioned.