CRYSTAL MORPHOLOGY AND PHASE IDENTIFICATIONS IN POLY(ARYL ETHER KETONE)S AND THEIR COPOLYMERS .1. POLYMORPHISM IN PEKK

Poly(ether ketone ketone) (PEKK) with all-para linkages in phenylene g roups is one member of the poly(aryl ether ketone) family. This polyme r has been reported to exhibit two polymorphisms (forms I and II) base d on wide-angle X-ray diffraction (WAXD) experiments. The form I cryst al structure has been determined to have two-chain orthorhombic packin g with a = 0.767 nm, b = 0.606, and c = 1.008 run. For form II, howeve r, two different structures have been proposed: both are orthorhombic, but with different size and symmetry.1,2 Through our morphological ob servations, two different crystal forms have been isolated. Using elec tron diffraction (ED) experiments combined with WAXD, we have found th at form II of PEKK should have a two-chain orthorhombic lattice. This unit cell dimension is consistent with the form II cell reported by Bl undell et al.,1 namely, a = 0.417 nm, b = 1.134 nm, and c = 1.008 nm. Two maps of the formation of these forms with crystallization conditio ns are also discussed.