Cold crystallization of narrow molecular weight fractions of PEEK

Several amorphous narrow molecular weight fractions of poly(aryl ether ethe r ketone) or PEEK have been heated from below their glass transition temper ature to above their final melting point. The semicrystalline morphology in duced by cold crystallization and its thermal evolution are studied by time -resolved simultaneous small-angle X-ray scattering (SAXS), wide-angle X-ra y diffraction, and differential scanning calorimetry. The long period and t he crystalline and the amorphous thicknesses are computed from the correlat ion function of the SAXS curves. The evolution of the structural parameters of the various semicrystalline samples can be reconciled with the existenc e of a single distribution of lamellae which undergoes reorganization durin g the continuous heating. The reorganization process as well as the semicry stalline morphology depends on the molecular weight of the fractions. The a morphous thickness strongly increases with the molecular weight while the t hermal evolution of the thickness of the crystalline layers is similar for all fractions. These experimental results support the view that the larger degree of entanglements of the high molecular weight samples impedes the re organization mechanism with the consequence that the apparent melting tempe rature decreases with increasing average molecular weight.