Polymerizing propylene

When mixed with Et2AlCl, the vanadium(III) complex (87) polymerizes propylene at —78 °C in a living manner.241,242 Poor initiator efficiency ( 4%) and low activities were improved by employing complex (88) activities of lOOgmmol h bar 1 were reported and the polymerization of propylene remained living (Mw/Mn= 1.2-1.4) up to 40 °C.243 244 The synthesis of end-functionalized PP and PP copolymers has also been achieved using these initiators. 

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

The isotacticities and activities achieved with nonbridged metallocene catalyst precursors were low. Partially isotactic polypropylene has been obtained by using a catalyst system of unbridged (non-ansa type) metallocenes at low temperatures [65]. A chiral zirconocene complex such as rac-ZrCl2(C5H4 CHMePh)2 (125) is the catalyst component for the isospecific polymerization of propylene (mmmm 0.60, 35% of type 1 and 65% of type 2 in Scheme Y) [161]. More bulky metallocene such as bis(l-methylfluorenyl)zirconium dichloride (126) together with MAO polymerized propylene to isotactic polypropylene in a temperature range between 40 and 70°C [162]. 

W.L. Gladfelter, University of Minnesota Can you polymerize propylene with your tantalum catalyst ... 

Collins et al. reported in 1995 that catalysts based on hafnium are desirable for the production of elastomeric polypropylene in that they polymerize propylene to a high molecular weight polymer and are indefinitely stable under typical polymerization conditions [8], Based on the theory that hafnium as a catalytic center leads to a significant increase of molecular weight in propene polymerization compared with the zirconium-based catalyst, Rieger et al. searched for hafnocene systems to obtain polymers with new properties. 

MPC [Mitsui Petrochemical] A continuous process for polymerizing propylene, based on the Ziegler-Natta process, but using a much more active catalyst so that de-ashing (catalyst removal) is not required. The catalyst contains magnesium in addition to titanium successive versions of it have been known as HY-HS (high yield, high stereospecifity), HY-HS II, and T-catalyst. Developed jointly by Mitsui Petrochemical Industries, Japan, and Montedison SpA, Italy, in 1975, and now licensed in 56 plants worldwide. 

Natta A process for polymerizing propylene and other higher olefins, catalyzed by crystalline titanium trichloride and an alkyl aluminum compound such as triethyl aluminum. The polymer can exhibit various types of stereoregularity, depending on the catalyst and the conditions. Invented in 1954 by G. Natta at the Istituto de Chimica Industrial del Politecnico di Milano, Italy, and commercialized in 1957. Now used widely, worldwide. See also Ziegler, Ziegler-Natta. 

Carbon dioxide can itself be used as a feedstock as well as a solvent for the synthesis of aliphatic polycarbonates by precipitation polymerization. Propylene oxide [39] and 1,2-cyclohexene oxide [40] can both be polymerized with CO2 using a heterogeneous zinc catalyst (Scheme 10.21). 

Bis(benzamidinate) zirconium catalysts (Figure 9, complexes F9-1 and F9-2) can polymerize propylene monomers into highly isotactic polypropylene (MAO up to 98% [mmmm, T = A9°C) at 25 °G in CH2CI2 under 9.2atm of propylene monomer, as expected from the G2-symmetric octahedral structure of the catalysts. The polymer-... 

The method employed to calculate the total number of active centers relies upon the determination of the variation occurring in the ratio between ethyl groups (deriving from the alkylaluminum) which are present in the polymer and the whole amount of polymerized propylene, on increasing the time of polymerization. 

In Fig. 34 has been plotted the specific radioactivity (corrected for the radioactive contamination) and the corresponding number of —CjHa groups found in the polymer against the polymerized propylene mols. 

By assuming that stereoselectivity is connected to the regular heterogeneous catalyst surface, Natta introduced violet T1CI3 and used preformed heterogeneous catalysts in further studies.234,240 These complexes may act as stereoselective catalysts and polymerize propylene to crystalline stereoregular polymers. 

Activities of the catalysts for polymerizing propylene oxide in bulk at 30° C were compared on the basis of the weight of polymer formed per weight of catalyst per unit time. Zinc hexacyanocobaltate itself was a fairly active catalyst, giving 300 grams of polymer per gram of... 

Soluble catalysts based on vanadium compounds polymerize propylene to polypropylene of syndiotactic or atactic structure 73 sc,. Both types of polypropylenes are soluble in hydrocarbons, independent of the molecular weight of the polymers, even at a low temperature of —78 °C. Therefore, the polymerization system remains homogeneous during the polymerization. 

Doi, Ueki and Keii47,48) have found that the soluble catalyst composed of V(acac)3 (acac = acetylacetonate anion) and A1(C2H5)2C1 polymerizes propylene in toluene at —78 °C to give a syndiotactic living polypropylene having a narrow molecular weight distribution (Mw/Mn = 1.05-1.20). This low-temperature polymerization of propylene was shown to satisfy all criteria for the living polymerization 47). 

Price and co-workers [33,34,35) studied a number of aluminum alkyls for their effectiveness in polymerizing propylene oxide and obtained up to 50% reaction in two weeks at 25° C. The proportion of... 

In a typical 80,000 tons/year plant, capital costs were about 220 per metric ton in 1974. To produce 1000 kg of polymer, 1030 kg of monomer is needed, together with 1 kg of hydrogen and 25 kg of diluent. Catalyst and miscellaneous chemicals cost about 4 per 1000 kg of polyethylene pellets produced. For production, 300 kg of medium-pressure steam, 800 kg of low-pressure steam, 530 kWh of electrical energy, 200 m3 of water, 30 m3 of nitrogen, and 600 m3 of air are also required. To polymerize propylene in suspension, the same technology can be used. Catalysts now available [based on TiCl3 (see Table II)] make it unnecessary to separate isotactic from atactic materials. 

A final example of a stereoselective heterogeneous catalytic system is the work of Laycock, Collacott, Skelton and Tchir.17 Layered double hydroxide (LDH) synthetic hydrotalcite materials were used to stereospecifically polymerize propylene oxide [PO] to crystalline isotactic and liquid atactic poly(propyleneoxide) [PPO]. These authors suggest that the LDH surface acts as other inorganic or organometallic coordination initiators or catalysts by providing specific surface orientations for propylene oxide monomer. X-ray powder diffraction showed some loss of crystallinity after calcination and X-ray photoelectron spectroscopy showed an enhancement of Mg/Al content due to restructuring of the Mg and A1 surface atoms. The surface was also rich in Cl ... 

Transition Metal Catalyst Systems for Polymerizing Propylene... 

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