Heterogeneity in polymer melts from melting of polymer crystals

Semi-crystalline polymers containing amorphous and crystalline regions usually have intimately mixed chains. The resulting topological constraints (entanglements) in the amorphous regions limit the drawability in the solid state. By controlled synthesis the number of entanglements can be reduced. Ultimately, crystals composed of single chains are feasible, where the chains are fully separated from each other. If such separation can be maintained in the melt a new melt state can be formed. Here we show that through slow and carefully controlled melting such polymer crystals form a heterogeneous melt with more entangled regions, where the chains are mixed, and less entangled ones, composed of individually separated chains. Chain reptation, required for the homogenization of the entanglement distribution, is found to be considerably hindered. The long-lived heterogeneous melt shows decreased melt viscosity and provides enhanced drawability on crystallization. This novel route to create heterogeneous melt should be applicable to polymers in general.