Crystallization and morphology of metallocene polyethylenes with well-controlled molecular weight and branching content

✍ Scribed by Ya Peng; Qiang Fu; Fang-Chyou Chiu

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 370 KB
• Volume: 52
• Category: Article
• ISSN: 0959-8103
• DOI: 10.1002/pi.1038

✦ Synopsis

Abstract

The crystallization and morphology of some metallocene polyethylenes with well‐controlled molecular weight and branching content were investigated by DSC, WAXD, PLM and SALS. The banded spherulites observed in linear PE are not seen in crystallization of branched PEs. The small spherulites with small lamellae or fringed micelle crystals are formed when branching content is higher, as suggested by PLM and SALS. The expansion of the unit cell was observed by WAXD as the molecular weight and branching content increased. At even higher branching content (more than 7 mol%), a shrinkage of the unit cell was seen, probably due to a change of crystal morphology from lamellar‐like crystals to fringed micelle‐like crystals. Crystallization temperature, melting point and crystallinity are greatly decreased for branched PEs compared with linear PEs. The equilibrium melting temperature cannot be determined via the Hoffman–Weeks approach for branched PEs since T~m~ is always 5–6 °C higher than T~c~ and there is no intercept with the T~m~ = T~c~ line. Our results show a predominant role of branches in the crystallization of polyethylene.

© 2003 Society of Chemical Industry