Electron-microscopic investigation of the morphology of a melt-crystallized polyaryletherketone

Abstract

We have studied the structure and morphology of the useful high‐temperature/high‐strength polymer polyaryletherketone (PEEK) by transmission electron microscopy and three‐dimensional electron diffraction after finding suitable solvents (α‐chloronaphthalene and benzophenone) that allowed casting of the required ultrathin polymer films. When crystallized from the melt, PEEK grows in the form of spherulites consisting of narrow lamellae and having the b axis of the unit cell radial. Additionally, at high temperatures in these ultrathin films, the spherulites attain an extraordinary cylindrical symmetry as a result of growth of their lamellae on edge, with the c crystallographic direction parallel to the film plane and the a direction corresponding to the cylinder axis. Reasons for this mode of growth are attributed to the highly anisometric molecular cross section normal to the chain direction, which favors crystal nucleation on the substrate with the bc plane. At lower temperatures during crystallization from the melt, a more random lamellar disposition is seen in these thin‐film spherulites, although lamellae on edge still predominate. Crystallization by heating from the quenched glassy phase yields random lamellar aggregates and small spherulites. The glassy phase in ultrathin PEEK shows no consistent morphological features down to a level of resolution of 1.0 nm. Scanning electron microscopic examination of the free surfaces of bulk samples crystallized under controlled conditions both from the melt and from the glass, show that our findings from ultrathin films (with the exception of the quasicylindrical spherulitic substructure) also apply to these thicker specimens.