TIME-RESOLVED X-RAY STUDY OF POLY(ARYL ETHER ETHER KETONE) CRYSTALLIZATION AND MELTING BEHAVIOR .2. MELTING

Heating measurements of amorphous and isothermally crystallized (260-3 20-degrees-C) samples were carried out using time-resolved small-angle X-ray scattering (SAXS) to study the melting behaviour of poly(aryl e ther ether ketone) (PEEK). In the amorphous sample, the scattering max imum became detectable after the cold crystallization, with the peak p osition q(max) decreasing with temperature. The latter was also seen i n crystallized samples. Two types of long period (L(B) and L(C)M) were determined, by using Bragg's law and the correlation function, respec tively. These values are inversely proportional to q(max), and therefo re they all increased with temperature. In the crystallized samples, t wo stages of increase in the long period were found: below the lower m elting temperature of the double endotherms (T(m1), determined by d.s. c.), the increase was small, while above T(m1), both of the long perio ds increased rapidly. In addition, the invariant Q was found to increa se with temperature but reached a maximum near the onset temperature o f the last endotherm. These results were consistent with the hypothesi s of sequential melting of lamellar bundles consisting of two populati ons of thickness. In the crystalline specimens, the increase in Q was mainly due to the thermal expansion, whereas in the amorphous sample, the larger increase in Q was additionally attributed to the broad cold crystallization.