CRYSTAL MORPHOLOGICAL INVESTIGATION IN THIN-FILMS OF POLY(ARYL ETHER KETONE KETONE) HAVING A META-LINKAGE

The lamellar crystal morphology of thin films of poly(aryl ether keton e ketone) having a meta-linkage (PEKK(I)) is observed under transmissi on electron microscopy (TEM), utilizing samples with different thermal histories and preparation procedures. After isothermal crystallizatio n from the melt, a double endothermic behaviour can be found through d ifferential scanning calorimetry (d.s.c.) experiments. Partial melting of PEKK(I) can be obtained by heating the samples to a temperature be tween these two endotherms. By comparing the TEM morphological observa tions of the samples before and after partial melting, it can be shown that edge-on lamellar crystals, having different thermodynamic stabil ities, form during isothermal crystallization. After partial melting, only the type of lamellar crystal exhibiting the higher thermodynamic stability remains. Small angle X-ray scattering (SAXS) results exhibit a change in the long period of the lamellar crystals before and after the partial melting process. For the solution-induced crystallization of PEKK(I), only a single endotherm exists in the d.s.c. observations . After annealing at high temperatures, however, a double endothermic behaviour appears. This also results in a decrease in the long period observed by SAXS. The double population of the lamellar crystals is di fficult to observe in TEM, since the lamellar crystals in these thin f ilm samples possess a random, rather than an edge-on, orientation. Det ailed TEM imaging for observing these lamellar crystals is discussed. (C) 1997 Elsevier Science Ltd.