Interdependencies between the evolution of amorphous and crystalline regions during isothermal cold crystallization of poly(ether-ether-ketone)

We have studied the isothermal cold crystallization of poly(ether-ether-ket one) (PEEK) by atomic force microscopy, densitometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small- and wide- angle X-ray scattering (SAXS and WAXS), A two-stage process was clearly evi denced. The first stage results in the progressive consumption of free amor phous regions by growing spherulites. Lamellae grow in tightly packed bundl es, with no evidence for a random insertion mechanism. DSC and DMA consiste ntly show the progressive disappearance of the alpha(1) relaxation typical of the initially amorphous PEEK. Simultaneously, a new relaxation appears a few degrees higher (alpha(2) relaxation) and develops at the expense of al pha(1) relaxation. It corresponds to the formation of amorphous regions con strained by neighboring crystals. On the basis of a simple simulation, we s how that the experimental data in this second stage of crystallization can be accounted for by a simple stack thickening process in which new lamellae are progressively added in parallel to previously formed lamellar stacks.