On the effect of reaction conditions on morphology of aromatic poly(ether-ketone)s, PEKK

Aromatic poly(ether ketone ketone)s (PEKKs) of regular structure, containing 1,3- and 1,4-substituted phthalic acid units in a 1-to-1 ratio, were prepared by two methods: electrophilic and nucleophilic aromatic substitutions. Electrophilic preparations were performed as low-temperature precipitation polycondensations, and resulting polymers were obtained in the form of particles. Nucleophilic syntheses were carried out in N-cyclohexyl-pyrrolidone and diphenyl sulfone at 260 degreesC and 290 degreesC, respectively, in the presence of sodium and potassium carbonates. Differential scanning calorimetry (DSC) curves of the polyketones as obtained and reprecipitated revealed differences in their thermal behavior depending on the polymerization method, the synthetic route, and the reaction conditions used. The ability of samples to undergo molecular reorganization during heating, affected by polymerization conditions, is responsible for the diversity of DSC curves observed. A parallel X-ray study of the samples revealed small differences between diffractograms from the as-obtained materials, while they were similar for the reprecipitated ones. However, X-ray diffractograms of thermally treated samples showed further differences between the emerging crystalline structures that should be related to a different chain organization produced during the polymerization process.