Ultra-high molar mass polyethylene(UHPE) or HDPE was melted at various temperatures or at a constant temperature for various time, and then crystallization from the melt was investigated. The crystallization behavior of UHPE was found to be different from those of HDPE. It was found that the crystallization temperature decreased as the heating time or heating temperature increased. During the melting process, thermal motion of the chains leads to a change of chain conformation from parallel-extended chains to interpenetrated random coils, accompanied by the occurrence of entanglements. As a result, the crystallization temperature shifts to a lower temperature. In addition, the samples of UHPE with less entanglement were prepared by a freeze-drying procedure from dilute solution was proved the effect of entanglements on crystallization behavior of macromolecules. A preliminary study on the crystallization of the samples indicates that entanglements have a pronounced effect on the crystallization behavior of macromolecules.
