MAO-catalyst

To prepare unbedded catalyst, polymerization was first carrirf out in a small a tetui glass reactor at room temperature for 1 hr in n-heptane at very low styreaie (xmcentration using Et[Ind]2ZrCl2/MAO catalyst with Al/Ti mole ratio of20-200. After the rraiction, a small part of the solid fraction (embedded catalyst) was isolated fi om the liquid phase for the... 

The catalyst jnecursors were tested in solution polymerization runs at 1.3 bar of elhylene pressure in toluene at tempraature (Tp) between 10 and 50 C and the results are summarized in Table 1. The active catalysts are generatKl in situ in toluene by the addition of MAO to the catalyst precursor in the prraence of ethylme. Methyl substituted catalyst (3a/MAO) showed the highrat activity while isopropyl homologue (3c/MAO) the lowest activity. The 3a/MAO catalyst showed higher activity than 3c/MAO by 2-fold at low Tp (say 10 C). However, as Tp... 

Polystyrene-g-poly(ethylene oxide) was synthesized by the copolymerization of styrene and styrenic PEO with CpTiCb/MAO catalyst [190]. In this case the macromonomer was prepared by first reacting the sodium salt of PEO-OH with NaH and then with a 5-fold amount of p-chloromethyl styrene. 

The active species of the metallocene/MAO catalyst system have now been established as being three-coordinated cationic alkyl complexes [Cp2MR] + (14-electron species). A number of cationic alkyl metallocene complexes have been synthesized with various anionic components. Some structurally characterized complexes are presented in Table 4 [75,76], These cationic Group 4 complexes are coordinatively unsaturated and often stabilized by weak interactions, such as agostic interactions, as well as by cation-anion interactions. Under polymerization conditions such weak interactions smoothly provide the metal sites for monomers. 

The initial Group 4 metallocene/MAO catalyst systems has some disadvantages ... 

At present, the difficulties described in 7-9 can be solved. The use of MAO can be avoided by the use of non-MAO catalysts such as cationic Group 4 metallocenes or neutral Group 3 metallocenes. It has been found that the molecular weight of the resulting polymer can be increased by introducing substituents at the 2,5-position in the cyclopentadienyl group of the... 

Bis(imino)pyridine Iron Halide/MAO and Cobalt Halide/MAO Catalysts. 120... 

Zirconocene catalysts, 16 79, 82 Zirconocene complexes, 16 89, 91 Zirconocene concentration, 16 94 Zirconocene-MAO catalysts, 16 93, 114 Zirconocenes, doubly bridged, 16 107 Zirconocene systems, 16 93 Zirconocenium—borate catalysts, 16 96... 

Three stereoisomers are possible in the cholestanylindene-derived zir-conocene complexes illustrated in Scheme 67. Two are racem-like, and the other is meso-like depending on the geometry of the metallocene moiety. The stereochemistry of the reaction is controlled by both the structure of the metallocene skeleton and steroidal substituent. Polymerization of propylene with 0-C activated with MAO gave polypropylene of 240,000, about 40% mmmm approximately 70% is due to enantiomorphic site control and the rest is due to chain-end control. Use of the catalyst derived from a /3-A-B mixture produced a mixture of polymers. The a-A and a-B/MAO catalysts afforded isotactic poly-... 

Terminally brominated PE as PE macroinitiator can be produced by other methods. It has been reported that vinyl terminated PE produced by a bis(phenoxy-imine)metal complex and MAO catalyst system (Mn = 1800, Mw/Mn = 1.70) was converted to terminally 2-bromoisobutyrate PE through the addition reaction of 2-bromoisobutyric acid to the vinyl chain end. Polyethylene-Wodc-poly( -bulyl acrylate) (PE-fo-PnBA) from terminally brominated PE by ATRP procedure has also been produced [68]. It was reported that degenerative transfer coordination polymerization with an iron complex can be used to prepare terminally brominated PE as a macroinitiator [69]. A Zn-terminated PE prepared using an iron complex and diethylzinc,... 

PE-g-PS graft copolymer was produced by a coupling reaction, too. a-Carboxyl PS prepared by an ATRP technique was reacted with PE-g-glycidyl methacrylate (GMA) to produce PE-g-PS [121]. A PP-fc-PMMA block copolymer was synthesized using a magnesium bromide terminated PP as an initiator for the radical polymerization of MMA, which was prepared from the vinylidene terminated PP obtained with the Et(Ind)2ZrCl2/MAO catalyst system [122],... 

Arndt, M. and Kaminsky, W., Microstructure of Poly(cycloolefin)s Produced by Metallocene/Methylaluminoxane (mao) Catalysts . Macromol. Symp., 97, 225-246 (1995). 

Copolymerization Parameters for Ethylene/a-Olefin Copolymerization with Various Metallocene/MAO Catalysts 1... 

The tacticities are also different, depending on whether the metallocene is supported. The homogeneous Me2C(CpFlu)ZrCl2/MAO catalyst gives a higher yield of syndiotactic polypropylene than the supported catalyst (Fig. 26). 

Fig. 27. Vinyl polymerization of cyclopentene and norbornene is possible using metalo-cene/MAO catalysts (137).

Fig. 28. Dependence of the glass transition temperature of ethylene/norbornene copolymers produced by various metallocene/MAO catalysts on the incorporation of norbornene (24).

Fig. 29. Polymerization of styrene by Cp TiCl3 and Cp TiFj/MAO catalysts at various temperatures and Al/Ti ratios. Cp TiCl3 = 6.3 x 10 4 mol/liter Cp TiF3 = 6.3 x 10 5 mol/liter (24).

Fig. 30. Possible microstructures of poly(methylenecyclopentane) produced by metal-locene/MAO catalysts from 1,5-hexadiene (137).

Entry Catalyst [Catalyst] (mmol) MAO/catalyst Ratio Activity1 (xlO-3)... 

The zirconocene/MAO catalysts are about 10-100 times more active for ethene polymerization than the conventional Ziegler systems. Using bis(cyclopen-tadienyl) zirconium dichloride Cp2ZrCl2 and MAO up to 40000000 g, poly-ethene/g Zr-h are obtained (Table 2) [54]. 

Table 2. Polymerization activity of [Cp2ZrCl2]/MAO catalyst applied to ethene in 330 ml of toluene...

Table 5. Copolymerization parameters for ethene/a-olefin copolymerization by using different metallocene/MAO catalysts...

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

Of great industrial interest are the copolymers of ethene and propene with a molar ratio of 1/0.5, up to 1/2. These EP-polymers show elastic properties and, together with 2-5 wt% of dienes as third monomers, they are used as elastomers (EPDM). Since they have no double bonds in the backbone of the polymer, they are less sensitive to oxidation reactions. As dienes, ethylidenenorbomene, 1,4-hexadiene, and dicyclopentadiene are used. In most technical processes for the production of EP and EPDM rubber in the past, soluble or highly disposed vanadium components are used [69]. Similar elastomers can be obtained with metallocene/MAO catalysts by a much higher activity which are less colored [70-72]. The regiospecificity of the metallocene catalysts toward propene leads exclusively to the formation of head-to-tail enchainments. The ethylidenenor-bornene polymerizes via vinyl polymerization of the cyclic double bond and the tendency to branching is low. The molecular weight distribution of about 2 is narrow [73]. 

In the mid-1980s the first metallocene/MAO catalysts for the isotactic polymerization of propene were described. Ewen found Cp2TiPh2/MAO to produces isotactic polypropene at low temperatures by chain end control mechanism (stereoblock structure). When using a mixture of racemic and meso [En(Ind)2] TiCl2 in combination with MAO, he obtained a mixture of isotactic and atactic polypropene, the isotactic polymer having a microstructure in accordance with... 

Table 7. Comparison of the productivity, molecular weight, melting point and isotaeticity obtained in polymerization experiments with various metallocene/MAO catalysts (bulk polymerization in 11 liquid propene at 70 °C, Al/Zr ratio 15000) showing the broad range of product properties) [96]...

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