Analysis of microstructure of ethylene–1-hexene copolymer prepared over thermally pretreated MgCl2/THF/TiCl4bimetallic catalyst

✍ Scribed by Young Soo Ko; Taek Kyu Han; Hajime Sadatoshi; Seong Ihl Woo

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 226 KB
• Volume: 36
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(19980130)36:2<291::aid-pola12>3.0.co;2-j

✦ Synopsis

Thermally pretreated catalysts were prepared by heating MgCl 2 /THF/ TiCl 4 (TT-0) at 80ЊC for 5 min (TT-1) and 60 min (TT-2), and at 108ЊC for 5 min (TT-3) and 60 min (TT-4). Ethylene-1-hexene copolymers were prepared with these catalysts. The TT-1 catalyst produced more blocky and higher 1-hexene content polymer than TT-0, 2, 3, and 4. Temperature rising elution fractionation (TREF) analysis was used to investigate the chemical composition distribution of the ethylene-1-hexene copolymer, exhibiting bimodal distribution for TT-0 and trimodal for TT-1, 2, 3, and 4. A portion of higher hexene content of the copolymer markedly increased when the copolymerization was performed with TT-1, indicating that copolymerization active sites were newly generated. Portion of homopolyethylene increased drastically when the copolymerization was performed with TT-4, indicating that ethylene homopolymerization active sites were increased. Gel permeation chromatography (GPC) also revealed that three kinds of active sites existed on the catalyst. 13 C-NMR spectrum of each fraction after TREF analysis suggested that the isospecific active site could polymerize 1-hexene well, resulting in random and alternating copolymers. A scheme for generation of the active site and change of its nature during thermal treatment of bimetallic complex catalyst is proposed.