A latent entanglement model: Effects of irregularities of the crystallite surface on polymer draw

In a previous study on the drawing of polyethylene nascent reactor powders, the maximum achievable uniaxial draw ratio, DR, was found to be strongly dependent on prior synthesis conditions. Samples synthesized at 85 degrees C by a slurry process had the highest ductility. Synthesis at lower temperatures (60 and 30 degrees C) led to samples of lower DR. The highest achievable ductility is believed to correspond to the lowest entanglement density, but simple models suggest that lower synthesis temperatures should produce fewer entanglements. However, low crystallization temperatures lead to irregular fold surfaces, and these irregularities or defects can convert into entanglements when folded chain segments are drawn out of the crystals into more extended conformations. We have called these defects `'latent entanglements''. This concept can explain experimental data on the structure and drawability of certain classes of nascent reactor powders and can prove helpful to the goal of tailoring ductility by control of synthesis.