Effect of molecular weight on high pressure crystallization of linear polyethylene. II. Physical and chemical characterizations of crystallinity and morphology

The high pressure crystallized specimens described in the preceding paper (1) were characterized by X‐ray diffraction, density, and differential scanning calorimetry, Nitric acid etching, followed by gel permeation chromatography and DSC on the residues provided further characterization of the morphology. The crystallinity decreased from 100 to 80 percent with increasing molecular weight, over the range Mw = 4.9 × 104 to 4.6 × 106. The crystallites were predominately in extended chain morphology, but the percent in extended chain form decreased from 98 to 85 percent over the indicated molecular weight range. In all cases, there was a wide, bimodal or multi‐modal, distribution of lamellar thickness. The physical characterization results were consistent with and complementary to the results from electron microscopy. The large differences in crystallinity and gross morphology readily account for observed molecular weight dependent differences in mechanical properties.