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
Octamethyloctahydrodibenzofluorenyl: Electronic Comparisons between a Sterically Expanded Ligand and Its Cyclopentadienyl Analogues
Incorporating the octamethyloctahydrodibenzofluorenyl (Oct) ligand into metallocene and constrained geometry olefin polymerization catalysts has profound catalytic consequences. The steric influences are undoubtedly important, but it is shown herein that electronics likely also play a crucial role. The electron richness of the Oct− anion was directly measured by competitive deprotonation experiments, which reveal that the pKa of OctH is 3.9 units higher than that of fluorene. The HOMO−LUMO gap decreases by about 0.6 kcal/mol for each additional tertiary alkyl group appended to the metallocene R2C(C5H4)(C13H8)ZrCl2 (R = Me or Ph) in the 2, 3, 6, and 7 positions of the fluorenyl moiety, indicating the ability of these groups to increase the HOMO energy by electron donation. The carbonyl stretching frequencies for η5-OctMn(CO)3 (2009, 1924 cm−1) demonstrated that the Oct ligand is the most electron donating in the series of CpMn(CO)3, Cp*Mn(CO)3, and (C13H9)Mn(CO)3. DFT calculations universally corroborate t...
Copolymerization of ethylene and α-olefins with combined metallocene catalysts. II. Mathematical modeling of polymerization with single metallocene catalysts
The relation between the polymerization conditions and the distributions of molecular weight (MWD) and chemical composition (CCD) of poly(ethylene-co-1-hexene) made with single supported metallocene catalysts was investigated. Understanding the behavior of each metallocene under different polymerization conditions is necessary for designing combined metallocene catalysts to produce tailor-made polyolefins. In this article, a simple mathematical model based on experimental results is developed and combined with the bimodality criterion developed in Part I of this series to predict polymerization conditions and metallocene combinations that will produce polymers with desired MWDs and CCDs. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1417–1426, 2000