Melting and morphology in melt-crystallized meta-linked poly(aryl ether ketone)

Unique thermal behavior and accompanying morphology in meta-linked poly(ether diphenyl ether ketone) (PEDEKm) melt-crystallized at various conditions was analyzed. The two widely spaced and well-resolved melting peaks (Tm,1 and Tm,2) in PEDEKm offered a unique model for proposing a more advanced interpretation on the complex and highly controversial issues of multiple melting and crystalline morphology commonly seen in semi-crystalline polymers. There are two main lamella types of different thickness populations, whose melting peaks labeled P1 and P2 may appear in series giving two melting endotherms at 302 and 322°C, respectively. However, despite the series appearance of two melting peaks upon scanning, only one type of lamellae preferentially exists in the melt-crystallized PEDEKm depending on processing temperatures/histories. When isothermally crystallized at lower temperatures (290°C or lower), PEDEKm possesses only the P1 crystal, which may or may not be melted/re-crystallized into thicker P2 crystal entity depending on heating rates or annealing temperature/time. A break-off temperature for lamellar thickness in PEDEKm is about 300°C. When crystallized at 300°C or higher, PEDEK developed only the P2 crystal, which is mainly a thickened and branched axialite. This study also demonstrated that the unit cell remained unchanged for either the P1 or P2 crystal entities.