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

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2004-12, Vol.224 (1), p.97-103
• Main Authors: Skeřil, Robert, Šindelář, Pavel, Salajka, Zdenek, Varga, Vojtech, Císařová, Ivana, Pinkas, Jiří, Horáček, Michal, Mach, Karel
• Format: Article
• Language: English
• Subjects: Applied sciences; Constrained geometry catalysts; Copolymerization; Copolymerization ethene–styrene; Copolymers ethene–styrene; Crystal structures; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts; Titanium
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2004.06.034

Catalysts 1/MAO– 3/MAO at molar ratios Al/Ti = 900 and styrene/ethene = 10 at 50 °C produced pseudo-random copolymer containing up to 47.8 mol% of incorporated styrene. ▪ The ethene–styrene copolymerization has been investigated using the dimethylsilylene-bridged (amidocyclopentadienyl)dichlorotitanium(IV) complexes [TiCl 2{η 5-1-(SiMe 2N t-Bu-κN)-2,3,4-Me 3-5-R-C 5}], 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.