Crystallization Study of Poly(ether Ether Ketone)/Poly(ether Imide) Blends by Real-Time Small-Angle X-Ray Scattering

Morphological changes during isothermal melt crystallization in poly(aryl ether ether ketone) (PEEK)/poly(ether imide) (PEI, Ultem® 1000) blends were monitored via real-time small-angle x-ray scattering (SAXS) using synchrotron radiation. SAXS data were analyzed using a novel combination of correlation and interface distribution functions to determine the lamellar crystal thicknesses l_c and interlamellar noncrystalline or "amorphous" layer thicknesses l_a. The higher glass transition noncrystalline PEI component slows the PEEK crystallization substantially, but l_a (about 40 Å) and l_c. (about 85 Å) are independent of crystallization time and blend composition. This is consistent with the known independence of melting temperature with blend composition. These results indicate that PEEK crystallizes in densely crystalline lamellar stacks through all stages of primary crystallization, and that the noncrystalline PEI is almost entirely excluded from the stacks at all times during spherulitic growth. The rate of increase in scattering invariant is found to be reduced during spherulite impingement due to spatial limitations.