TEMPERATURE-DEPENDENT CRYSTALLINE-AMORPHOUS STRUCTURES IN ISOTACTIC POLYPROPYLENE - SMALL-ANGLE X-RAY-SCATTERING ANALYSIS OF EDGE-BOUNDED 2-PHASE SYSTEMS

Small-angle X-ray scattering (SAXS) experiments on isothermally crysta llized isotactic polypropylene (iPP) reveal a clear temperature depend ence of the crystalline-amorphous structure over a broad range of temp eratures below the crystallization temperature. This phenomenon is ana lyzed using SAXS combined with dilatometry. A new concept for the eval uation of SAXS data-the specific length of edges L(s)-is used. It allo ws a quantitative interpretation of g''(0), the second derivative of t he electron density correlation function at r = 0. Using this paramete r, a clear identification of the relevant physical process is possible . Whereas primary crystallization leads to the formation of laterally extended crystalline lamellae, subsequent cooling generates additional small crystallites in the amorphous regions. A model relating this mo de of partial crystallization and melting to the special morphology of iPP-the cross-hatched structure-is suggested.