Ziegler/Natta catalysts, diene polymerization

Within the context of lanthanide chemistry it is interesting to note reports by Chinese (10,15) and Russian (12) scientists that activities of lanthanide-based Ziegler-Natta catalysts for polymerization of 1,3-dienes show much higher activity for early metals than for the end-row metals Er-Lu. The potential for higher activity analogs of the complexes described here is thus evident. ... 

Coordination polymerization of isoprene using Ziegler-Natta catalyst systems (Section 6 21) gives a material similar in properties to natural rubber as does polymerization of 1 3 butadiene Poly(1 3 buta diene) is produced in about two thirds the quantity of SBR each year It too finds its principal use in tires... 

Conjugated dienes are among the most significant building blocks both in laboratories and in the chemical industry [1], Especially, 1,3-butadiene and isoprene are key feedstocks for the manufacture of polymers and fine chemicals. Since the discovery of the Ziegler-Natta catalyst for the polymerizations of ethylene and propylene, the powerful features of transition metal catalysis has been widely recognized, and studies in this field have been pursued very actively [2-7]. 

The initiation of polymerizations by metal-containing catalysts broadens the synthetic possibilities significantly. In many cases it is the only useful method to polymerize certain kinds of monomers or to polymerize them in a stereospecific way. Examples for metal-containing catalysts are chromium oxide-containing catalysts (Phillips-Catalysts) for ethylene polymerization, metal organic coordination catalysts (Ziegler-Natta catalysts) for the polymerization of ethylene, a-olefins and dienes (see Sect. 3.3.1), palladium catalysts and the metallocene catalysts (see Sect. 3.3.2) that initiate not only the polymerization of (cyclo)olefins and dienes but also of some polar monomers. 

Friebe, L., Nuyken, O. and Obrecht, W. Neodymium Based Ziegler/Natta Catalysts and their Application in Diene Polymerization. Vol. 204, pp. 1-154. 

In discussions about the nature of the active species in the polymerization of dienes by Ziegler/Natta catalyst systems allyl species have already been suggested in the 1960s [273-278]. This discussion has continued through the past decades [139,279-283]. Today, it is widely accepted that Nd-allyl-groups are the key element in the insertion of dienes into the Nd carbon bond. 

In the polymerization of dienes with Ziegler/Natta catalyst systems it is a well-established fact that the presence of halide donors is essential in order to achieve high catalytic activities and high cis-1,4-contents [360,361]. The halide free catalyst system NdO/TIBA is a good example for a catalyst with a poor performance and a high trans- 1,4-specificity [362,363]. For various binary and ternary catalyst systems the qualitative impact of chlorides on the stereochemistry of BR is demonstrated in a series of fundamental experiments the results of which are summarized in (Table 5) [364],... 

The activation energies available for binary and ternary catalyst systems are in a range from 20 to 70 kj mol x, which according to Odian is characteristic for polymerizations mediated by Ziegler/Natta-catalysts [456]. It is interesting to note that the polymerization of dienes catalyzed by NdCl3-based catalyst systems show lower activation energies than Nd-carboxylate-based catalyst systems. The influence of halide donors on the temperature depen-... 

As discussed in Sects. 2.1 and 2.2.8 control of molar mass is an important aspect in the large-scale polymerization of dienes. In Nd-catalyzed polymerizations the control of molar mass is unique amongst Ziegler/Natta catalyst systems as standard molar mass control agents such as hydrogen, 1,2-butadiene and cyclooctadiene which are well established for Ni- and Co-systems do not work with Nd catalysts [82,206,207]. The only known additives which allow for the regulation of molar mass without catalyst deactivation are aluminum alkyls, magnesium alkyls, and dialkyl zinc. 

The primary use of TiCl3 is as a catalyst for the polymerization of hydrocarbons (125—129). In particular, the Ziegler-Natta catalysts used to produce stereoregular polymers of several olefins and dienes, eg, polypropylene, are based on CC-TiCl3 and A1(C2H5)3. The mechanism of this reaction has been described (130). Suppliers of titanium trichloride include Akzo America and Phillips Petroleum in the United States, and Mitsubishi in Japan. 

Gao, W. and Cui, D.M. (2008) Highly cis-1,4 selective polymerization of dienes with homogeneous Ziegler-Natta catalysts based on NCN-pincer rare earth metal dichloride precursors. Journal of the American Chemical Society, 130, 4984. 

Polymerization of Conjugated Dienes with Heterogeneous Ziegler-Natta Catalysts... 

The structure of the polymer obtained in the polymerization of butadiene and isoprene with heterogeneous Ziegler-Natta catalysts depends on the nature of the monomer, catalyst system, and reaction conditions. Previously reported results are reviewed and a mechanism is proposed for the stereoregulated polymerization of conjugated dienes. The polymerization of cyclopentadiene with LiAlH -TiCl4 or LiAlR4-TiCl4 catalyst system yields a readily oxidized polymer for which a 1,2-structure is proposed. 

In addition to titanium-based Ziegler-Natta catalysts, vanadium-based systems have also been developed for PE and ethylene-based co-polymers, particularly ethylene-propylene-diene rubbers (EPDM). Homogeneous (soluble) vanadium catalysts produce relatively narrow molecular mass distribution PE, whereas supported V catalysts give broad molecular mass distribution.422 Polymerization activity is strongly enhanced by the use of a halogenated hydrocarbon as promoter in combination with a vanadium catalyst and aluminum alkyl co-catalyst.422,423... 

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