The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Styrene was copolymerised with ethylene using the catalyst systems [rac-Et(H 4 Ind) 2 TiCl 2 ]/MAO and [rac-Et(H 4 Ind) 2 ZrCl 2 ]/MAO. Keeping other experimental variables under control, we tested different styrene/ethylene ratios in the reactor feed. It was found that the titanium-based catalyst showed very low activity even for ethylene homopolymerisation...
Single site olefin polymerisation catalysts are suitable candidates for modelling purposes. Their well-defined structure and the almost complete elucidation of their polymerisation mechanisms, make these organometallic complexes ideal for studies based on quantitative structure-activity relationships (QSAR). Although the QSAR technique is extensively used in drug design, there are very few reports...
The effect of temperature on extrusion rheometry of single site metallocene-catalyzed polyethylenes and polyethylene copolymers is investigated. Samples of molecular weight, M w , ranging from 90,000 to 330,000 and short-chain branching degree (SCB) from 0 to 21.2 CH 3 /1000C, as well as samples with a small amount of long-chain branching, are analyzed. It is observed that all the...
This report describes complete density functional theory studies performed to elucidate ethylene polymerisation mechanisms of the Brookhart-type catalysts N,N'-(2,6-dimethylphenyl)ethylenediimine nickel (II) and N-(2,6-dimethylphenyl)pyridine-2-carboxaldiimine nickel (II). Both catalysts showed conformations that blocked the active site and thus hindered ethylene coordination. These conformations...
This report describes a computational DFT study, based on the hybrid density functional B3LYP method, designed to investigate the hydrogenolysis process that occurs in ethylene polymerisation catalysed by a nickel-bulk diimine catalyst (N,N'-bis(2,6-diisopropylphenyl)-2,3-butanediimine nickel(II) methyl cation [{(2,6-( i Pr) 2 Ph)N C(Me)-C(Me)=N(2,6-( i Pr) 2 Ph)}NiCH...
A computational study of the ethylene–styrene copolymerization with rac-ethylenebis(tetrahydroindenyl)MCl 2 [M=Ti, Zr] systems using DFT methods is presented. The complexation, coordination and insertion energies for ethylene and styrene monomers as well as for the styrene–ethylene copolymerization steps into the catalytic active site models [Et 2 (IndH 4 ) 2 ]MCH ...
A combined QM/MM study of the ethylene/1-hexene copolymerisation with bisiminepyridine iron(II) is presented. It has been found experimentally that these catalysts do not copolymerise ethylene with 1-hexene. Based on the mechanism of propagation and termination processes proposed by Deng et al., we have performed calculations for the ethylene and 1-hexene monomers in order to give a suitable explanation...
We have found a branching dependence of critical extrusion temperature in metallocene-catalysed linear and branched polyethylene, below which the commonly found surface distortion instabilities disappear. The elimination of these extrusion instabilities has been observed in a wide range of temperatures up to 23°C above the melting point of each polymer. However, in contrast to previous observations,...
In this work we present the first attempt to study the copolymerization process of ethylene with styrene by computer simulation. Density functional theory calculations have been carried out on the detailed mechanism of ethylene-styrene copolymerization using non-bridge half-sandwich cationic species, generated by the system CpTiCl 3 activated with the methylaluminoxane cocatalyst. The goal...
DFT calculations have been carried out on the cationic species for the two different Brookhart's catalyst systems: [{ArN CH-HC NAr}NiR''] + (3a) and [{ArN CMe-MeC NAr}NiR''] + (3b) (where Ar={2,6-C 6 H 3 (Me) 2 } and R''=Me). These calculations reveal that the conformation of aryl groups attached to nitrogen atoms could provide a suitable explanation for...
Alkylamidinate complexes have been recently reported to be useful catalysts for olefin polymerisation as an alternative to metallocene systems. The present work reports theoretical calculations performed at DFT level for ethylene insertion reactions in zirconium and titanium alkylamidinate compounds with variable structural complexity. The energy barriers obtained for these reactions show that these...
Hydrogenolysis is a commonly used method to control the molecular weight or size of polymers obtained by Ziegler–Natta and related metallocene catalysts. However, the precise mechanism governing these controlling processes is still unknown. It is most accepted that the insertion of hydrogen molecule into the metal–alkyl bond of the catalyst active species competes favorably against the ethylene insertion...
A variety of techniques is used to describe the fine structure of a series of well defined linear polyethylenes, polymerized using the new generation of metallocene-based catalysts. The sample's molecular weight (M w ) is restricted to the usual values of processability of this material ranging from 14K to 460K. It will be clearly shown that the overall enthalpy of the rapidly crystallized...
Dynamic and steady state flow measurements and shrinkage experiments have been carried out to investigate the influence of blend composition on viscous and elastic properties of a new type of polyolefin: high density polyethylenes of high and low molecular weight obtained via metallocene catalysts. The polyethylenes are characterized by narrow molecular weight distribution and absence of branching...
A combined WAXD and d.s.c. study on blends of a series of commercial high density and low density (LD) polyethylene (PE) samples rapidly crystallized from the melt is presented. The melting curves of the materials are extensively analysed and compared to those exhibited by the individual components. The results, besides being indicative of a full compatibility of the two components, allow one to...
The ab initio method at the Hartree-Fock level has been used on two zirconocene systems, the unbridged Cp 2 ZrCH +3 and the bridged (Si(CH 3 ) 2 )Cp 2 ZrCH +3 compounds. For each complex the insertion of an ethylene molecule has been followed from reactant to product through the corresponding transition states. The calculated activation energies...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.