Effect of Substituent on Titanocene/MMAO Catalyst for Ethylene/1-Hexene Copolymerization
Copolymerization of ethylene with 1-hexene was carried out using two ansa-fluorenyl titanium derivative complexes. The substituent effect on the catalytic activity, monomer reactivity ratio and polymer property was investigated. It was found that the presence of t-Bu groups on fluorenyl ring exhibited remarkable catalytic activity and produced polymer with high molecular weight. However, these catalysts produce polymer with narrow molecular weight distribution, indicating the characteristic of single-site metallocene catalyst. Based on C NMR, we can observe that monomer reactivity ratio was affected by catalyst structure. The rH values of complex 2 were lower than that of complex 1 which might be result from the higher steric hindrance leading to a reduction of 1hexene insertion step. Keywords—Constrained geometry catalyst, linear low density polyethylene, copolymerization, reactivity ratio
Ethylene/α‐olefin copolymerization by nonbridged (cyclopentadienyl)(aryloxy)titanium(IV) dichloride/AliBu3/Ph3CB(C6F5)4 catalyst systems
A series of nonbridged (cyclopentadienyl) (aryloxy)titanium(IV) complexes of the type, (η5-Cp′)(OAr)TiCl2 [OAr = O-2,4,6-tBu3C6H2 and Cp′ = Me5C5 (1), Me4PhC5 (2), and 1,2-Ph2-4-MeC5H2 (3)], were prepared and used for the copolymerization of ethylene with α-olefins (e.g., 1-hexene, 1-octene, and 1-octadecene) in presence of AliBu3 and Ph3CB(C6F5)4 (TIBA/B). The effect of the catalyst structure, comonomer, and reaction conditions on the catalytic activity, comonomer incorporation, and molecular weight of the produced copolymers was examined. The substituents on the cyclopentadienyl group of the ligand in 1–3 play an important role in the catalytic activity and comonomer incorporation. The 1/TIBA/B catalyst system exhibits the highest catalytic activity, while the 3/TIBA/B catalyst system yields copolymers with the highest comonomer incorporation under the same conditions. The reactivity ratio product values are smaller than those by ordinary metallocene type, which indicates that the copolymerization of ethylene with 1-hexene, 1-octene, and 1-octadecene by the 1–3/TIBA/B catalyst systems does not proceed in a random manner. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Ethylene/1‐hexene copolymers synthesized with a single‐site catalyst: Crystallization analysis fractionation, modeling, and reactivity ratio estimation
A series of poly(ethylene-co-1-hexene) samples made with rac-ethylene bis(indenyl)zirconium dichloride/methylaluminoxane were analyzed by crystallization analysis fractionation (CRYSTAF). The nine samples had comonomer contents of 0–4.2 mol % 1-hexene with a narrow range of molecular weights (34,000–39,000 g/mol). Because all the copolymer samples had narrow, unimodal chemical composition distributions, they were ideal as calibration standards for CRYSTAF. A linear calibration curve was constructed relating the peak crystallization temperature from CRYSTAF operated at a cooling rate of 0.1 °C/min and the comonomer content as determined by 13C NMR. Reactivity ratios for ethylene and 1-hexene were estimated by the fitting of reactant liquid-phase compositional data to the Mayo–Lewis equation. It was found that a value of the 1-hexene reactivity ratio could not be unequivocally determined from the set of samples analyzed because the range of comonomer incorporation was too narrow. Stockmayer's bivariate distribution was used to model the fractionation process in CRYSTAF, and although a good fit to experimental CRYSTAF profiles was attained, the model did not fully describe the underlying crystallization phenomena. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2595–2611, 2002