THE CRYSTAL LAMELLAR MORPHOLOGY OF AN AROMATIC POLYKETONE WITH UNUSUAL CRYSTALLIZATION AND MELTING BEHAVIOR

Wide-angle and small-angle X-ray scattering and differential scanning calorimetry are used to elucidate the lamellar morphology of an aromatic polyketone (designated PK99). PK99 has three unusual crystallization and melting characteristics. First, there is a coupled melting and recrystallization process at around 260-degrees-C, well below the final melting point of 306-degrees-C; this process suggests two crystal forms. Secondly, there are two maxima in the growth rate versus temperature characteristics. Thirdly, the melting point is relatively low compared with the T(g) (158-degrees-C). WAXS shows that above and below the 260-degrees-C process there is no essential difference in the crystal packing. However, WAXS and SAXS data do show small step differences in crystal perfection and in lamellar thickness. The lamellar thicknesses are comparable to the periodic repeat length. This produces a new situation not normally observed in other crystalline polymers, where more than one type of lamellae can be formed containing different chain sequences. The unusual characteristics can be explained in terms of these different types of lamellae.