Ethene, polymerization, with

I 2 Microstructure Control of Ethene Homopolymers Through Tailored Ni,Pd(ll) Catalysts Tab. 2.3 Ethene polymerizations with nickel catalysts 6a-d/MAO. ... 

I 3 Highly Active Ethene Polymerization Catalysts u/ith Unusual Imine Ligands Tab. 3.7 Ethene polymerization with iron diimine pyridine/MAO 66-69... 

Fig. 3.11 Ethene polymerization with bis[(2,5-dichlorophenyl)imine]-2,6-diacetimine iron dichloride and various concentrations of MAO. (A) yield, (B) molecular weight Mn, (C) chains/aluminum.

Fig. 3.14 Graphical representation of ethene polymerization with 2-hydroxyimine nickel compounds. Stick plot (A) and corresponding...

Table 5 Ethene polymerization with metallocene/methylaluminoxane catalysts.

Table 2 Comparison of ethene polymerization with different metallocene/MAO catalysts at the same polymerization conditions...

At 24 °C and 15-60 bar ethylene, [Rh(Me)(0H)(H20)Cn] catalyzed the slow polymerization of ethylene [4], Propylene, methyl acrylate and methyl methacrylate did not react. After 90 days under 60 bar CH2=CH2 (the pressure was held constant throughout) the product was low molecular weight polyethylene with Mw =5100 and a polydispersity index of 1.6. This is certainly not a practical catalyst for ethylene polymerization (TOP 1 in a day), nevertheless the formation and further reactions of the various intermediates can be followed conveniently which may provide ideas for further catalyst design. For example, during such investigations it was established, that only the monohydroxo-monoaqua complex was a catalyst for this reaction, both [Rh(Me)3Cn] and [Rh(Me)(H20)2Cn] were found completely ineffective. The lack of catalytic activity of [Rh(Me)3Cn] is understandable since there is no free coordination site for ethylene. Such a coordination site can be provided by water dissociation from [Rh(Me)(OH)(H20)Cn] and [Rh(Me)(H20)2Cn] and the rate of this exchange is probably the lowest step of the overall reaction.The hydroxy ligand facilitates the dissociation of H2O and this leads to a slow catalysis of ethene polymerization. 

Heat treatment of carbon black impregnated with a salt of [Fe(phen)3] gives an oj gen reduction catalyst. i The compounds [Fc2(88)Cl4], [Fe(89)Cl2] and [Fe(90)Cl2] are potential ethene polymerization catalysts they all contain five-coordinated iron(II). The chiral terpy ligands (91) (R R = all three combinations of H, Pr ) and the Schiff base analogue (92), also... 

Acyclic diene metathesis polymerization (ADMET) is a related polymerization in which an unconjugated diene polymerizes with loss of ethene [Lehman and Wagener, 2002, 2003 Schwendeman et al., 2002], ADMET is carried out using the Schrock and Gmbbs initiators at about 40-80°C. The process is a step polymerization, not a ROP chain reaction. The reaction is reversible, and high polymer MW is achieved by removal of ethene (usually by reduced... 

Ethene can be polymerized with peroxide catalysts under high pressure (1000 atm or more, literally in a cannon barrel) at temperatures in excess of 100°. The initiation step involves formation of radicals, and chain propagation entails stepwise addition of radicals to ethene molecules. 

Screening of these zirconium species for ethene polymerizations using MAO activation gave only moderate activities (Table IV).40 It was suggested that interactions of aluminum with the phosphinimide nitrogen atom led to ligand abstraction... 

C to form the dinuclear (butadienyl)zirconium system 120. Treatment with B(C6F5)3 leads to the formation of a mono-addition product (121), even in the presence of excess borane. Complex 121 (Scheme 40) shows only a marginal ethene polymerization activity. This led to the notion that such formation of dimeric zirconium complexes might represent desactivation pathways in homogeneous Ziegler-Natta catalyst chemistry.125... 

Fig. 26. IR time-resolved spectra of ethene polymerization reaction on (a) nearly stoichiometric and (b) reduced a-Cr2C>3 samples CH3 and CH2 stretching mode regions. Continuous curves, IR spectra taken at 10-s intervals (a) and 7-s intervals (b) in the presence of P = 5.32 kPa of ethene dashed curves after a total contact time of 30 (a) and 8 min (b) and ethene removal by outgassing at room temperature curves on the bottom, ethene gas [reprinted with permission from Scarano etal. (493), Copyright 1994 American Chemical Society].

Fig. 39. IR time-resolved spectra of ethene polymerization reaction on Cr/silica. Last spectrum after 15 s [adapted from Zecchina et al. (506) with permission from Elsevier Science Publishers],...

An enormous increase (factor up to 1 million) in activity was found in 1975 at the University of Hamburg when water was added in a ratio of A1(CH3)3 H20 = 1 2 and, in 1977, using the isolated reaction product of methylaluminoxane (MAO) together with titanocenes and zirconocenes (Cp2Ti(CH3)2, Cp2Zr(CH3)2, Cp2ZrCl2) as catalysts for ethene polymerization [26,27]. In these combinations, metallocenes become more active than commercially used Ziegler catalysts. 

An interesting effect is observed for the polymerization with ethylene(bisin-denyl) zirconium dichloride and some other metallocenes (Fig. 5). Although the activity of the homopolymerization of ethene is very high, it increases when copolymerizing with propene [66]. 

Studies of ethene copolymerization with 1-butene using the Cp2ZrCl2/ MAO catalyst indicated a decrease in the rate of polymerization with increasing comonomer concentration. 

Apart from the novel ring-opening reaction with THF, [SmCp 3] inserts RNC and CO and is an ethene polymerization catalyst. Another reaction uncharacteristic of [LnCp3] systems... 

If the polymerization reaction occurs in the presence of steric constraints, the activation energy associated with the monomer insertion grows with the progress of the reaction, in the same way as discussed for the oligomerization reactions catalyzed by Bronsted acid sites (Section LB and Fig. 2a), because the available space is progressively reduced. Under such conditions, the formation of polymeric species is limited, and small oligomeric species can become observable. An example of this situation is ethene polymerization on Cr/silicalite, in which the transition metal center is grafted to the internal surface of a cavity (Section VI.C.l). 

Fig. 22. IRES spectra collected in situ during the first stages of the ethene polymerization reaction on a Cr(II)/Si02 catalyst, by using the catalyst as the radiation source. The four set of data show the spectral evolution as a function of the contact time from bottom to top at 10, 20, 30, and 40 s, respectively. Experimental data (dotted curves) are compared with the best fit (full curves) (unpublished).

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