Quantitative Structural Study of Cold-Crystallized PEKK

Poly(ether ketone ketone) (PEKK) is a semicrystalline polymer investigated for highly demanding applications in aerospace, transportation, electronics, and oil & gas industries. The properties required for these applications, such as thermomechanical and chemical stability, are intimately linked to the crystalline state of the material. PEKK exhibits a polymorphism that depends, among other factors, on its thermal history. The control and quantification of the crystalline state of PEKK is the subject of this study. Amorphous PEKK (T/I = 60/40, where T stands for terephthalic and I for isophthalic units) films were cold-crystallized at various crystallization temperatures, T-C, from 180 to 280 degrees C in a ventilated oven. Based on a quantitative analysis of small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) data, we propose for the first time a methodology to obtain detailed information about the crystalline state of PEKK: total crystallinity, relative amount and stability of crystalline forms, form I and form II, and melting enthalpy of 100% crystallized PEKK. The evolutions of each crystalline form and the total crystallinity with T-C were deduced. The amount of each crystalline form, form I and form II, can be tuned by controlling the heating rate to 280 degrees C. The evolution of the crystalline lamellar thickness and periodicity as well as the crystalline amount and cell parameters with T-C were interpreted and discussed in relation to the published results on PEEK, PEKK (100% T), and PEKK (100% I). Finally, the melting enthalpy of a 100% crystallized PEKK copolymer (T/I = 60/40), Delta H-m(100%) = (202 +/- 20) J/g, was estimated.

Automated summary

PEKK, a semicrystalline polymer, is crucial for applications in aerospace, transportation, electronics, and oil & gas industries due to its properties like thermomechanical and chemical stability linked to its crystalline state. This study proposes a methodology to control and quantify the crystalline state of PEKK by analyzing small-angle X-ray scattering, wide-angle X-ray scattering, and differential scanning calorimetry data. The evolution of crystalline forms and total crystallinity with different crystallization temperatures were discussed, and the melting enthalpy of a 100% crystallized PEKK copolymer was estimated.