CRYSTALLIZATION OF POLY(ARYL ETHER KETONES) .3. THE CRYSTAL-STRUCTURE OF POLY(ETHER ETHER KETONE KETONE) (PEEKK)

The unit cell of poly(ether ether ketone ketone) was determined to be orthorhombic, as in other poly(aryl ether ketones). Comparing different poly(aryl ether ketones) it was found that the crystallographic parameters depend on the ether to ketone ratio. With increasing ketone content, the dimensions of the a-axis decrease, whereas the dimensions of the b- and c-axes increase. The volume of the unit cell also increases. It could be shown that the crystallographic parameters also depend on the annealing conditions. This implies a variation of the crystallographic density, which, surprisingly, depends only on the annealing temperature and not on the ether to ketone ratio. These phenomena can be explained by changes in the packing of the molecules in the crystalline regions, which obviously depend on the thermal history. This has an influence on the X-ray diffraction pattern but not on the enthalpy of fusion. Therefore, determination of the degree of crystallinity should be carried out preferably using differential scanning calorimetry.