Ethylene homopolymerization

Each set of experiments was carried out under the same reaction condition except using different comonomers, i.e. p-methylstyrene, o-methylstyrene, m-methylstyrene and styrene, respectively. The compositions of copolymers were determined by H NMR spectra, and the thermal properties (melting point and crystallinity) were obtained by DSC measurements. Overall, all comonomers show no retardation to the catalyst activity. In fact, the significantly higher catalyst activities were observed in all copolymerization reactions (runs 2-5), comparing with that of ethylene homopolymerization (run 1). Within each set (runs 2-5 and 6-9) of comparative experiments, p-methylstyrene consistently shows better incorporation than the rest of comonomers, i.e. o-methylstyrene, m-methylstyrene and styrene. Both catalysts with constrained mono- and di-cyclopentadienyl ligands are very effective to incorporate p-methylstyrene into polyethylene backbone. In runs 2 and 6, more than 80 % of p-methylstyrene were converted to copolymer within one hour under constant (- 45 psi) ethylene pressure. On the other hand, only less than half of styrenes (runs 5 and 9) were incorporated into ethylene copolymers under the same reaction conditions. The significantly... 

The results of the MD simulations clearly demonstrate that the insertion starting from the higher energy isomers of the ethylene-chelate complexes in which the chelating bond has been broken have much smaller activation barriers, that are comparable to those observed in ethylene homopolymerization. This, however, does not explain the differences in the copolymerization activity of Pd and Ni-diimine complexes, as the barriers for the ethylene insertion into Ni-alkyl bond are smaller (14.2 kcal/mol) than those for Pd-alkyl bond (16.8 kcal/mol). Thus, it may be concluded that the ethylene insertion following the insertion of the polar monomer is not a crucial factor for the diimine catalyst copolymerization activity. It is the initial poisoning of the catalyst by formation of the... 

Figure 2 shows a series of cloud-point curves determined for the system ethylene-2-ethylhexyl acrylate-poly(ethylene-co-2-ethylhexyl acrylate). Each cloud-point curve corresponds to one stationary copolymerization condition in CSTR1. The compositions and concentrations referring to the five monomer-polymer mixtures, including one ethylene homopolymerization reaction (Experiment 1), are listed in Tab. 1. FA is the concentration of the acrylate units within the copolymer (in mole-%),/P and/A denote the concentrations of polymer and of acrylate monomer in the monomer-polymer mixture, respectively. As can be seen from Fig. 1 and from Tab. 1, increasing acrylate content in the copolymer lowers the cloud-point pressure. 

Such bis(pentamethylcyclopentadienyl) complexes exhibit extremely high activities in ethylene homopolymerization but the steric constraint of the permethylated rings does not allow insertion by higher a-olefins. Less constraining ligand environments like that in (6) (Figure 10) result in dimerization with consequent loss of activity. Compound (6) is a more... 

Ethylene homopolymerization High activity, highly linear, MJM = 2... 

Two cyclopentadienyl-sandwiched Cp2ZrX2/MAO complexes (Cp = cyclopentadienyl X = halogen or alkyl) with C2v-symmetry form the earliest metallocene system that has been used for ethylene homopolymerization with remarkably high activity. The application in propylene polymerization is less useful. They produce PP with low activity and low molecular weight.f Unexpectedly, the Cp2TiPh2/MAO system can be used for the synthesis of predominately i-PP below room temperature. The stereochemical structure of the resulting polymer indicates a chain-end-controlled model in the polymerization. Bridged C2v-symmetric... 

Fig. 16 Typical short-chain branching mechanisms for ethylene homopolymerization (A) formation of a butyl branch (B) formation of paired ethyl branches. (From Ref.. )...

Alexander KdppI was born in Vilseck, Germany, in 1970. He received his chemical education and his Ph.D. degree at the University of Bayreuth. His dissertation in the research group of Professor H. G. Alt dealt with new support materials for the immobilization of cocatalytically active alumoxanes and their application in ethylene homopolymerization and ethylene/a-olefin copolymerization. He is currently a chemist for BASF AG in Ludwigshafen, Germany. 

The Al-alkyl cocatalyst could also be introduced during the polymerization stage, with simultaneous interaction of catalyst with Al-alkyl cocatalyst and monomer within the polymerization reactor. Ethylene homopolymerization using Phillips catalyst PC600 calcined at 600°C followed by activation with TEA cocatalyst... 

Ethylene homopolymerization using Phillips catalyst PC600 calcined at 600°C followed by activation with DEAE cocatalyst during the slurry polymerization process was carried out with Al/Cr molar ratios of 7.5, 15.0, and 22.5 [84]. As shown in Fig. 14, a typical single-type polymerization kinetics corresponding to type b in Fig. 10b was observed, which was completely different from the kinetics with the same catalyst activated by TEA at the same conditions (as shown in Fig. 13). This t3 pe of polymerization kinetics could be ascribed to one type of active site (Site-B) formed in two ways. One was similar with the PC600 activated by TEA some chromate Cr(VI) species were reduced to Cr(II) species by ethylene monomer and coordinated with formaldehyde, then formaldehyde-coordinated Cr(ll) sites were transformed to DEAE-coordinated Cr(II) sites by substitution, as shown in Scheme 8. On the other hand, some chromate Cr(VI) species were reduced by DEAE, and then the Al-alkoxy product coordinated with the Cr(Il) sites. Site-B had relatively low activity and high stability. Based on the microstructure analysis, the relative amount of SCBs of polymers obtained from the DEAE systems was even more than that from TEA catalyst systems. This can be explained as follows. Firstly, the reduction ability of DEAE was weaker than that of TEA. More Cr(VI) species... 

Fig. 15 (a-c) Kinetic curves of ethylene homopolymerization using Phillips catalyst PC600/CO activated by TEA during slurry polymerization with Al/Cr mole ratio of (a) 7.5, ib) 15.0,and (c) 22.5. d-g) Kinetic curves of ethylene/1-hexene copolymerization under (d) Al/Cr ratio of 7.5 with 10 vol% of 1-hexene,... 

Liu, C., Tang, T, Wang, D., and Huang, B. 2003. In situ ethylene homopolymerization and copolymerization catalyzed by zirconocene catalysts entrapped inside functionalized mont-morillonite. Journal of Polymer Science, Part A Polymer Chemistry 41 2187-21%. 

Chain Propagation. Chain propagation proceeds by radical reaction with ethylene or comonomer molecules. In the case of ethylene homopolymerization, the mechanism and kinetics are straightforward. 

In this Scheme, wavy lines indicate both E and Z isomers are possible, but in practice, only the trans isomer derived from path (a) is observed.) The correspondence between unsaturation structure and last-inserted monomer does break down in certain documented cases (154), chain-end isomerization leads to a preponderance of raws-CHs—CH=CH—CH2P chain-termini from ethylene homopolymerization. 

Some new work on ethylene homopolymerization indicates that this mechanism may dominate, at least imder certain conditions (156). In fact, in the case... 

Jang Y-J, Nenov N, Klapper M, Mullen K (2003) Organic nanoparticles with polypropy-leneoxide chains as support for metallocene catalysts ethylene homopolymerization and ethylene/a-olefin copolymerization. Polym Bull 50 343-350... 

Professor Karl Ziegler was at the Max Planck Institute for Coal Research during this period working primarily with ethylene (Aufbau process) and much of his research that followed the initial discovery of the Miilheim catalyst (TiCl + AlEt ) dealt with ethylene homopolymerization and eth-ylene/propylene copolymerization. Before Ziegler disclosed his discovery in a technical publication, he disclosed his results to two industrial companies Montecatini of Italy and Goodrich-Gulf of the United States. 

This patent describes the reaction product obtained from the treatment of magnesium alcoholates such as Mg(OEt)2 with tetravalent titanium compounds such as TiC OR) or TiCl. Ethylene homopolymerizations and ethylene/1-butene copolymerizations were investigated and the polyethylene produced possessed a narrow molecular weight distribution as indicated from M /M values of 2-4 measured on the polyethylene samples. The polyethylene was described as especially suitable for the production of injection-molded articles. Catalyst Preparation 11 g of MgjOEt) was suspended in 50 ml of Diesel oil (boiling range of 130-160°C) and 200 ml of a 1 molar... 

Ethylene copolymerization reactions always proceed at substantively higher rates than ethylene homopolymerization reactions. Since ethylene is the most reactive olefin, addition of an a-olefin such as 1 -hexene would be expected to decrease the polymerization reaction, not increase the rate [73]. 

The reaction order n with respect to the partial pressure of ethylene (P ) or to the concentration of ethylene in solution (Cj) in the rate of an ethylene homopolymerization reaction (Rp, ) greatly exceeds first order ... 

For example, ethylene homopolymerization reactions were carried out in slurry at different ethylene concentrations. Plotting the total yield as a function of ethylene concentration gave n as high as 1.7-2.0. Also, by varying the P in gas-phase reactions and plotting the relative rate vs pressure, a reaction order of 1.8 was determined. 

Figure 2.16 Effect of hydrogen on kinetics of ethylene homopolymerization at 80°Cwith...

The reaction order n for each center with respect to in ethylene homopolymerization reactions was significantly greater than first order. 

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