CRYSTAL MORPHOLOGY AND PHASE IDENTIFICATIONS IN POLY(ARYL ETHER KETONE)S AND THEIR COPOLYMERS .2. YLENECARBONYL-1,3-PHENYLENECARBONYL-1,4-PHENYLENE)

The crystal structure and morphology of ylenecarbonyl-1,3-phenylenecar bonyl-1,4-phenylene) [PEKK(I)] containing one meta linkage in the thre e phenylene repeat units have been studied. Only one crystal form was found based on wide-angle X-ray diffraction (WAXD) and electron diffra ction (ED) experiments. The crystal unit cell possesses a two-chain or thorhombic lattice with a = 0.766 nm, b = 0.611 nm, and c = 1.576 nm. It is particularly interesting that the c-axis contains three phenylen e groups. Through our morphological observations, lamellar crystals ar e edge-on in most thin films. The crystal growth direction is along th e b-axis, and the a-axis is perpendicular to the film surface. The fla t-on lamellae can only be observed in the ''eye'' of the spherulites. The crystal unit cell dimensions change with the isothermal crystalliz ation temperatures. In particular, the c-axis shrinks drastically with increasing temperature. This can be attributed to the conformation ch anges in meta-linked phenylene groups, which is evident by comparing t he data for PEKK(I), PEKK with all-para-linked phenylene groups, and p oly(ether ether ketone) (PEEK).