Analysis of dual melting behavior in cold-crystallized poly(ether diphenyl ether metaketone)

By focusing on cold-crystallized poly(ether diphenyl ether metaketone) (PEKm), a more in-depth understanding of the nature of the crystalline morphology has been gained, which may lead to thorough mechanisms for interpreting the observed thermal behavior in PEKm. Apparently, cold-crystallized PEKm containing initially only a single PI crystal can exhibit dual melting peaks (300 and 320 degreesC), with the second high-melting peak corresponding to the P2 crystal that was subsequently formed via PI melting/repacking during the scan. However, dual morphism (preexisting PI and P2 crystals) could be intentionally introduced into PEKm if it was cold-crystallized at temperature schemes of decreasing order. The PI and P2 crystals possess the same unit cells (orthorhombic) and thus they differ only in the lamellae populations. The dual lamellar morphism in this PEKm sample also exhibited similar dual melting peaks during scanning, which correspond to melting of the individual PI and P2 in a sequential order. This study has thus provided important clues in and shed new light on the interpretation of multiple melting with respect to polymorphism in polymers. Relationships between the low-melting and high-melting lamellae in cold-crystallized polyketone polymer have been thoroughly explored.