Cold crystallization and polymorphism in an oligo(aryl ether ketone)

1,3-Bis(4-phenoxybenzoyl)benzene (1) was crystallized from the glassy state at different temperatures, T-c, above the glass transition temperature (T-g = 24 degrees C). Analysis of X-ray diffractograms and DSC thermograms revealed a new polymorphism: a one-dimensional order phase (G1) and a new crystal phase (G2). In both cases the molecules adopt a linear extended conformation. G1 appears for 30 degrees C < T-c < 35 degrees C and its structure is like that of a smectic phase A with the molecular axis normal to the layer planes. Upon thermal treatment above 35 degrees C G1 converts into the crystal phase G2 which shows an inproving lateral packing of the molecules upon heating. G1 and G2 show melting temperatures around 88 and 98 degrees C, respectively. Provided that the thermal treatment of the cold crystallizing sample is done under ambient conditions, G2 converts into the most stable crystal phase 2 (T-m = 130 degrees C). Similar thermal treatments carried out inside a DSC calorimeter under dry N-2-flow are not capable of provoking the change in the molecular conformation (from a linear extended to a V-conformation) involved in the crystal phase transition of G2 to phase 2.