A WAXD/SAXS/DSC study on the melting behavior of Ziegler–Natta and metallocene catalyzed isotactic polypropylene

✍ Scribed by Eric Bryan Bond; Joseph E. Spruiell; J. S. Lin

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 276 KB
• Volume: 37
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19991101)37:21<3050::aid-polb14>3.0.co;2-l

✦ Synopsis

A small-and wide-angle X-ray scattering study was performed on two metallocene catalyzed isotactic polypropylene (miPP) resins. The results were compared with two similar molecular weight Ziegler-Natta catalyzed isotactic polypropylene (zniPP) materials. Wide-angle X-ray diffraction (WAXD) results showed the existence of two crystalline structures in the metallocene samples, the ␣-monoclinic and ␥-orthorhombic crystal structure, with increasing relative amounts of ␥-orthorhombic phase as the lamellae thickness increased. Differential scanning calorimetry (DSC) scans exhibited a melting peak for each crystal structure. The metallocene resins had the same equilibrium melting temperature (186 Ϯ 2 °C) as the high tacticity Ziegler-Natta (ZNHT) resin, whereas a second Ziegler-Natta resin had a lower equilibrium melting temperature (178 Ϯ 2 °C). The equilibrium melting temperature for the ␥-orthorhombic crystal structure in the metallocene resins was found to be 178 Ϯ 4 °C. The results were explained by the distribution of defects within the miPP chains, generating higher fold surface free energies for the miPP resins.