End‐group analyses of the oligo‐ and polypropylenes produced with bis(phenoxy‐imine) Zr and Hf complexes with methylaluminoxane (MAO) indicate that the polymerization is initiated by two consecutive 1,2‐insertions and is terminated by a β‐H transfer following a 2,1‐insertion. Our data indicate that chain propagation occurs with prevailing 1,2‐regiochemistry but with considerable regioerrors, and with virtually no stereoselectivity.
The polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO. 相似文献
The catalytic properties of bis(phenoxy‐imine) Zr and Hf complexes incorporating perfluorophenyl groups with methylaluminoxane were investigated. The fluorinated complexes produced far higher‐molecular‐weight polyethylenes and ethylene/propylene copolymers with increased activities compared with the non‐fluorinated congeners. Moreover, the fluorinated complexes displayed a higher incorporation ability for propylene.
Polyethylenes and highly syndiotactic poly(propylene)s possessing chain end hydroxyl groups were synthesized by living polymerizations using L2TiCl2 [ 1 , L: C6F5NCH(2 O C6H3 3 tBu)]/MAO and functionalized α‐olefins, H2CCH(CH2)n Y [ 2 ; YOAlMe2, n = 4 ( 2a ); YOSiMe3, n = 9 ( 2b )]. Because the primary insertion of 2 to a cationic species L2Ti+ Me ( 3 ) derived from 1 /MAO is much faster than the successive secondary insertion of 2 , addition of an equimolar amount of 2 to 3 resulted in the quantitative formation of L2Ti+ CH2 CH(Me) (CH2)n Y [ 4 ; YOAlMe2, n = 4 ( 4a ); YOSiMe3, n = 9 ( 4b )]. These cationic species 4 served as functionalized initiators for the living polymerization of both ethylene and propylene and afforded polyolefins having extremely narrow molecular weight distributions and a hydroxyl group at the initiating chain end. The terminating chain end of the syndiotactic poly(propylene)s was also functionalized by adding an excess amount of 2b as a chain end capping agent to the living L2Ti–polymeryl species. Due to much slower insertion of the second molecule of 2b relative to the first one, the obtained polymers were end capped quantitatively by a single molecule of 2b . Telechelic syndiotactic poly(propylene)s were successfully synthesized through a living polymerization initiated by 4b and an end capping using 2b .
Bis(phenoxy‐imine) Zr complexes upon activation with Et3Al/(Ph3C)mHn[PMo12O40] · 8 H2O (average: m/n = 2:1) were demonstrated to be highly active catalysts for the polymerization of ethylene. One of the complexes formed narrow‐molecular‐weight distributed polyethylene ( 1.45) with a very high activity (5640 kg‐PE · mol‐cat−1 · h−1), representing the first example of a MAO‐ and borate‐free, highly active, single‐site catalyst system based on a Group 4 transition metal complex and a heteropoly compound.
Catalysis of ethylene with bis(phenoxy‐imine) Zr complexes activated with Et3Al/(Ph3C)mHn[PMo12O40] · 8 H2O. 相似文献
A new bis(phenoxy‐imine)Zr complex has been developed. This complex in conjunction with iBu3Al/Ph3CB(C6F5)4 at 70°C produces ultrahigh‐molecular‐weight amorphous ethylene/propylene copolymer with a weight‐average molecular weight of 10 200 000 g/mol versus polystyrene standards, which represents the highest molecular weight known for linear, synthetic copolymers to date. 相似文献
Summary: “True” initial polymerization rates can be calculated from the adiabatic temperature rise under isoperibolic conditions. They are much higher than initial polymerization rates measured by standard mass flow meter methods under quasi‐steady‐state conditions. These high initial rates are followed by a fast apparent deactivation (“attenuation”) until a constant (“plateau”) activity is reached at low polymerization yields of 2–3 g PP · (g catalyst)−1 caused by an “increasing degree of encapsulation” of active sites. Mass transfer limitations are not observed. Cross sectional SEM images of the polymer samples support these kinetic findings.
Rate of polymerization (g of PP · (g catalyst)−1 · h−1) and yield of polymerization (g of PP · (g catalyst)−1) as function of time. 相似文献
Though preparation procedures of heterogeneous Ziegler‐Natta catalysts for propylene polymerization are sophisticated, it is uncertain whether the nature of the active sites is similar or different for different preparation procedures. In this study, the effects of preparation procedures on the nature of the active sites were investigated by stopped‐flow polymerization in combination with microstructure analysis of polymers. Both basic and advanced types of catalysts showed the same two kinds of isospecific active site, which indicated little influence of the preparation method on the active site structure. On the contrary, the ratios of the two kinds of isospecific sites were not the same, resulting in variation of average polymer properties.
1‐Hexene polymerization was investigated with bis[N‐(3‐tert‐butylsalicylidene)phenylaminato]titanium(IV) dichloride ( 1 ) using iBu3Al/Ph3CB(C6F5)4 as a cocatalyst. This catalyst system produced poly(1‐hexene) having a high molecular weight (Mw = 445 000–884 000, 0–60°C). 13C NMR spectroscopy revealed that the high molecular weight poly(1‐hexene) possesses an atactic structure with about 50 mol‐% of regioirregular units. 相似文献
A series of new Ni(II) complexes of general formula Ni{ZNO} Br ( 2a‐i ) (ZNO = phenoxy/naphthoxy‐imine with pendant N‐ and O‐donor groups) were prepared and characterized by elemental analysis, IR spectroscopy, ESI‐HRMS, and by X‐ray crystallography for 2e . In the solid state, 2e features a monomeric structure with κ3 coordination of the monoanionic naphthoxy‐imine‐quinoline ligand onto the nickel center. Upon activation with MAO, both classes of nickel catalysts were able to produce selectively 1‐butene (81.5–92.1 wt%) with turnover frequencies (TOFs) varying from 3,100 to 24,300 mol(C2H4) mol (Ni)?1 h?1. Nickel precatalysts bearing phenoxy‐imine ligands were much more active than its naphthoxy analogous under the same conditions. The use of a mixture of cocatalysts (MAO/TMA or MAO/TiBA) resulted in poor activities; however the presence of TiBA in the milieu led to a significant improvement on selectivity for 1‐hexene (25.5 wt%). Under optimized conditions ([Ni] = 10 μmol, 30 °C, oligomerization time = 5 min, 20 bar ethylene, [Al]/[Ni] = 600), precatalyst 2c led to TOF = 59,900 mol(C2H4) mol(Ni)?1 h?1 and selectivity for 1‐butene of 89.5 wt%. 相似文献
In this study, novel carrier materials were synthesized by addition of metal dihalide compounds in the synthesis reaction of magnesium diethoxide using metallic magnesium, ethanol and iodine. Poly(propylene) polymerizations were then investigated with the MgCl2‐supported TiCl4 catalysts using these carrier materials. As results, magnesium diethoxide with extremely large particle sizes and spherical shapes were obtained and the angles of repose of PP particles obtained by using their catalysts as a flowability index showed high values. Furthermore, in order to confirm key points for excellent catalyst performance from detailed characterizations, SEM images, compositions and WAXS were measured.
The fluorinated FI–Ti catalyst bis[N‐(3‐propylsalicylidene)‐pentafluoroanilinato] titanium(IV) dichloride (PFI) combined with dried methylaluminoxane (dMAO) is investigated for ethylene/1‐hexene copolymerization at 50 °C under atmospheric pressure. The reaction shows good livingness and has a high activity at high [H]/[E] molar ratios up to 14. Ultrahigh molecular weight (>1.4 × 106 g mol−1) copolymers with high 1‐hexene content (>25 mol%) are prepared. Kinetic parameters of the copolymerization with PFI are determined. The first‐order Markov statistics applies and the product of the reactivity ratios r1r2 is close to 1, giving random unit distributions.
Suitably activated, (Cp*){N(tBu)C(Me)N(Et)}ZrMe2 is known to initiate the ‘living’ and isotactic‐selective polymerization of alk‐1‐enes, and it can be used to synthesize block copolymers and stereoblock polymers. We report a full molecular kinetic investigation of propene, but‐1‐ene, and hex‐1‐ene polymerization with a MAO‐activated catalyst system. By combining NMR microstructural polymer analysis with QM modeling of the active species, the complicated regio‐ and stereochemistry of the polyinsertion process, as well as the active chain‐transfer pathways, are investigated. The perspectives and limitations of this catalyst for application in (stereo)block polymerizations are discussed.