Polymorphic transitions in oligo(aryl ether ketone)s studied by real time X-ray scattering

The crystal phase transitions occurring in oligo(aryl ether ketone) samples were studied, in real time, by means of X-ray scattering using synchrotron radiation. One sample is a typical molecular compound with 7 aryl units (m 7) while the other two samples, containing 11 aryl units (pll and mil), exh ibit the presence of a polymeric component. In relation to the polymorphic transition previously reported for aromatic polyketones, the phase transiti on study of the sample pll clarifies the role of chain length in the therma l behavior of aromatic polyketones. The structural variations, due to cryst al phase transitions, as revealed by X-ray diffraction during heating of th e samples are not accompanied by the parallel changes in the DSC thermogram s. The two endothermic peaks observed for the samples pll and mil are assoc iated with the melting of crystals with short and polymeric chains. Althoug h the amount of polymer component reaches about 75% in the case of pll (30% for mil), it does not exhibit the double melting phenomenon commonly obser ved for aromatic polyketones. A structural mechanism is suggested to explai n the absence of such a phenomenon for the pll and mil samples.