HIGH-TEMPERATURE CRYSTALLIZATION AND MORPHOLOGY OF POLY(ARYL ETHER ETHER KETONE)

We have investigated the structure and morphology of the high-performance polymer poly(aryl ether ketone) (PEEK) crystallized at temperatures between 300 and 320-degrees-C. We found no support for suggested changes in crystal structure, growth face, growth direction, or gross spherulitic morphology. In addition to narrow, fibrous lamellae, we provide evidence for large, branch-like, composite lamellar stacks and for primary growth of lamellae in the form of bundles. We have discovered a second morphological form of PEEK in thin films grown at high temperatures. This consists of large (order of mu-m), faceted single crystals in a flat-on orientation (i.e., parallel to the substrate), having the same unit cell and b-axis preferred-growth direction as the usual fibrous PEEK lamellae. However, in contrast to the latter, their molecular chains are not parallel to the lamellar normal but inclined to it by 38.1-degrees about the b-axis, leading to {102}-type fold surfaces. Moreover, overgrowths of the usual fibrous PEEK lamellae are obtained in an edge-on orientation on the larger flat-on crystals. We show that both populations share the same b-axis growth direction and that the edge-on lamellae arise by quasi-epitaxial nucleation of their molecules along the [201] direction on the planes of their flat-on counterparts.