Copolymerization of ethene with styrene using CGC catalysts: the effect of the cyclopentadienyl ligand substitution on the catalyst activity and copolymer structure

详细信息    查看全文

• 作者：Skeril ; Robert ; &Scaron ; indel&aacute ; r ; Pavel ; Salajka ; Zdenek ; Varga ; Vojtech ; Cí ; sarov&aacute ; Ivana ; et. al.
• 关键词：Titanium ; Constrained geometry catalysts ; Copolymerization ethene&ndash ; styrene ; Copolymers ethene&ndash ; styrene ; Crystal structures
• 刊名：Journal of Molecular Catalysis. A, Chemical
• 出版年：2004
• 出版时间：December 15, 2004
• 年：2004
• 卷：224
• 期：1-2
• 页码：97-103
• 全文大小：143 K

文摘

The ethene–styrene copolymerization has been investigated using the dimethylsilylene-bridged (amidocyclopentadienyl)dichlorotitanium(IV) complexes [TiCl₂{η⁵-1-(SiMe₂Nt-Bu-κN)-2,3,4-Me₃-5-R-C₅}], where R = Me (1), H (2), Bu (3), Ph (4), 4-fluorophenyl (5), and but-2-en-2-yl (6) in combination with methylalumoxane (MAO) as catalysts. The nature of the substituent R strongly influenced the catalyst activity and selectivity and the copolymer microstructure and molecular weight. The catalysts derived from 1 to 3 were by about one order more active than those derived from 4 to 6. At the optimum Al/Ti molar ratio of 900, the highly active catalysts produced a pseudo-random copolymer (95–97 wt. % ) containing up to 47.8 mol % of incorporated styrene. The low-active catalysts gave mixtures of a pseudo-random copolymer (76–85 wt. % ) with polyethene (10 wt. % ) and polystyrene sequences (3–7 wt. % ). The X-ray diffraction crystal structures of 2 and 4 were determined. Comparison of crystal structures of 1 and 2 versus 4 and 5 revealed a slightly shorter distances Ti–Cg (Cg – centroid of the cyclopentadienyl ring) and slightly larger Cl–Ti–Cl angles in 1 and 2, indicating a higher electron density at the titanium atom. An electron attracting effect of phenyl or alkenyl substituents as well as their steric hindrance can account for a low catalytic performance of 4–6/MAO catalysts.