1-hexene polymerization

Hexene Polymerization Polymerization of 1-hexene (and also propylene) by the Kaminsky catalyst [(Cp2ZrCl2/(MeAlO) /toluene] differs fundamentally from that of ethylene in that beta hydrogen elimination is the only detectable chain transfer mechanism. Insertion of 1-hexene into the Zr-C bond in Cp2ZrCH3+ produces Cp2ZrCH2CH(CH3)C4H9+. The electron donating... 

Kinetics of Hexene Polymerization We have measured the kinetics of 1-hexene polymerization by the Kaminsky catalyst by following monomer consumption with time. 

Figure 4. Plot of normalized initial rate of hexene polymerization versus initial hexene concentration.

The structural analysis of Gp TiMe2(0-2,6-Pr12G6H3) and Gp TiMe(0Tf)(0-2,6-Pr12G6H3) has been described and the effect of the organoboron compounds as co-catalysts in 1-hexene polymerizations has been studied.867 The molecular structures of CpTiCl2(OCy),865 CpTiCl OPr1),868 and CpTiCl2[0-l-(4-methoxo-phenyl)cyclohexyl]869 have been determined. 

When the catalyst is not fully regioselective, chain release by a /3-H transfer after a secondary insertion with formation of internal double bonds is often observed. This has been reported for ethylene/a-olefin co-poly-mers, PP, and other polyolefins, as well as for 1-hexene polymerization with dialkoxide catalysts. The reaction is shown in Scheme 14 for the case of propylene, where kinetic studies have shown it to be a bimolecular process, following the rate law s/J/ -h=s / -h[sZr][m].217,257 [sZr] refers to the concentration of active Zr centers bearing a growing chain having a secondary propylene unit linked to the metal. 

Propagation rates of first order in monomer concentration have been reported for ethylene and for propylene in the case of aspecific metallocenes266 as well as for propylene polymerization with isospecific metallocenes activated with MAO, B(C6F5)3, and [PhsCHBlCftFsL].290 297 Moreover, first-order kinetics were also observed for 1-hexene polymerization with the [ra(r-G2H4( 1 -Ind)2ZrMc [ McB(Gf,l 3)3. 156... 

Using deuterium-labeling experiments, about 100% of the metal was shown to be active in 1-hexene polymerizations with the [rar -C2H4( 1 -lnd)2ZrMc [McB((4,f5)3] catalyst,922 and the reactivity of M-(secondary alkyl) bonds at —80 °C was comparable to that of primary alkyl metallocenes.302 These relative monomer insertion rates appear strongly ligand specific. However, when these comparisons are made, it must be borne in mind that different authors use very different catalysts, as well as different definitions of the term active center Landis defined the active... 

Pre-catalysts with coordination 4 at the metal and a coordinating N-N ligand include complexes with chelating and dianionic diamide ligands. Activation of these pre-catalysts leads to a class of systems with remarkable catalytic properties and, not surprisingly, these systems have been quite deeply investigated.275,1066-1084 The MAO- and B(C6F5)3-activated diamide complexes 86 and 87, known as McConville catalysts, were introduced for 1-hexene polymerization in 1996.1066,1069... 

Dialkoxides with an extra donor atom have been also tested as ethylene, propylene, and 1-hexene polymerization catalysts.1 The first reports showed that an additional sulfur donor results in quite high ethylene and... 

C3-symmetrical tripodal ligands have been used to obtain amido complexes of family (86). If chiral substituents are present in the ligand periphery, some stereo discrimination is observed in the reaction with several chiral ketones and aldehydes. On the other hand, such systems can generate early-late heterobimetallics with metal-metal bonds (equation 41). Reaction of (91) with MeNC as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Tris (pyrazolyl) borate see Tris(pyrazolyI)borates) Zr and Hf complexes are other interesting examples of the type (86). In combination with MAO, they give promising results in ethylene and ethylene/hexene polymerizations. Substitution of these sterically crowded ligands allows adjustements of the environment of the active site to the... 

Schrock et al. have developed tridentate diamido/ donor ligand [(Bu-d 6-N-o-C6H4)20] ([NON] ) and prepared the corresponding Zr complex for ethylene and living 1-hexene polymerizations. Upon activation. FAB abstracts the apical methyl group of [NON]ZrMe2 to form a cationic species (65) analogous... 

Platinum complexes show none of the catalytic activity found in palladium and nickel complexes. This chemical inertness makes platinum a useful model for the more active catalysts. There has been a suggestion that platinum complexes of chiral a-diimines might lead to stereoselective olefin polymerization. Chiral camphor-based ligands have been employed in palladium complexes for ethylene polymerization, but there was no mention of stereoselectivity in hexene polymerizations. 

Figure 4-22. Variation of the reciprocal molar optical rotation [0] with tacticity jCf and for poly[(S)-4-methyl-l-hexene] polymerized under various conditions from a monomer of 93% optical purity. Tacticity was determined by IR. (After P. Pino et al.)...

FIGURE 13.3 Chelating bis(naphtholate) (14) and bisfphenolate) (15) group 4 polymerization precatalysts exhibit different behavior for 1-hexene polymerization when activated with MAO. 

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