Propylene electron donors

Catalytic activities of these complexes for the polymerization of propylene oxide were tested. The pyridine complex had no catalytic activity, whereas the diethyl ether or dioxane complex had activity comparable to that of the mother organozinc compound. This fact indicates that a strong electron donor which cannot be replaced by propylene oxide inhibits the polymerization effectively. Thus, the co-... 

Tani,H., Oguni,N. Stereospecilic polymerization of propylene oxide by N,N-bis(ethylzinc)-t-butylamine electron donor complex of catalyst and its implication for polymerization mechanism. J. Polymer Scl B7, 769 (1969). 

The copolymerisation of propylene oxide and carbon disulphide was carried out with a catalyst consisting of diethylzinc and an electron donor, such as tertiary amine, tertiary phosphine or hexamethylphosphoric triamide, in... 

The addition of a third component to the metal-alkyl is a widespread practice with MgCI2 catalysts in order to improve their performance and to control the polymer molecular structure. In ethylene polymerization the addition of modifiers (alkyl-halides, Lewis acids such as A1C13, halogens such as I2, and others) is rather limited and is principally used to modify the MWD (see Table 11 in Ref.53)). On the other hand, the addition of modifiers is almost indispensable to obtain satisfactorily stereoregular propylene polymers. The additives used for this purpose are generally electron donor compounds (Lewis bases) and a wide variety has been described in patent and scientific literature. 

For example, supported TiCl4/MgCl2 catalysts show a short period of acceleration, followed by a prolonged steady period 92,93). However, in the presence of electron donors, they may show the typical decay rate kinetics observed during propylene polymerization 93). Bulk catalysts prepared by interaction of TiCU with Mg(OR)2 show either a stationary rate, or a non-stationary rate, according to the titanium content 88,94). Bulk catalysts prepared by reduction of TiCl4 with organomagnesium compounds show a decay type rate 92-95>. 

As has been previously mentioned, electron donors are widely used as stereoregulating agents for the propylene polymerization with Mg/Ti catalysts. The addition of donors to highly active MgCl2/TiCl4—AlEt3 systems usually results in a remarkable increase... 

The existence of a further type of active centers was demonstrated by Pino and Rotzinger93> by polymerizing ethylene with a MgQ2-supported catalyst in the presence of an electron donor. A comparison of the ethylene and propylene kinetic curves shows that, while propylene polymerization is characterized by the well known rapid decrease in rate, the ethylene polymerization rate increases reaching a constant value after about 30 min. This has been attributed to the existence of active... 

The use of electron donors is of particular importance for propylene polymerization, where a severe control on polymer stereoregularity is required. 

The most simple artificial system consists of cofacial bis-quinone cyclo-phanes in which the two quinones have different redox potentials. Extreme differences in relative orientations have been realized with the ortho and geminal isomers in which a tetracyanoquinomethane oxidant and dimethoxy hydroquinone reduc-tants are connected by two propylene bridges (Fig. 7.2.4). A strong broad charge transfer band (600-1000 nm) was observed for the geminal isomer (e = 35(X)) and a weaker one for the ortho isomer (e = 120), indicating the importance of the relative orientation of electron donors and acceptors (Staab and BCnaus, 1979). 

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