Crystal Morphology and Phase Identification in Poly(Aryl Ether Ketone)s and Their Copolymers. 4. Morphological Observations in PEKK with all p-Phenylene Linkages

The thin film crystalline morphology of poly(aryl ether ketone ketone) having all p-phenylene linkages [PEEK(T)] has been investigated via transmission electron microscopy (TEM) and electron diffraction (ED) experiments. PEKK(T) samples isothermally crystallized from both the melt and the quenched glassy state over a temperature range of 160-360 °C have been examined, and two polymorphs (form I and form II) have been found. At low supercoolings, micrometer-size faceted single lamellar crystals can be found either from the melt or from the glassy state for both forms I and II. On the basis of ED results obtained from the single lamellar crystals, the c-axis in both forms is not perpendicular to the substrate. This leads to different single crystal shapes observed experimentally. Chain folding along the α-axis is recognized on the basis of the evidence from polymer decoration and lamellar microdeformation experiments. With decreasing crystallization temperature, spherulitic texture becomes dominant and an edge-on type of narrow ribbon-like lamellar orientation in the spherulites is increasingly distorted. The morphology of PEKK(T) obtained via solvent-induced crystallization by methylene chloride shows very small crystallites having a size less than 50 nm in three dimensions.