Patents, Ziegler-Natta catalysts

Complexation of the initiator and/or modification with cocatalysts or activators affords greater polymerization activity (11). Many of the patented processes for commercially available polymers such as poly(MVE) employ BE etherate (12), although vinyl ethers can be polymerized with a variety of acidic compounds, even those unable to initiate other cationic polymerizations of less reactive monomers such as isobutene. Examples are protonic acids (13), Ziegler-Natta catalysts (14), and actinic radiation (15,16). 

Interestingly a Ziegler Natta catalyst (Chapter 7) consisting of TiCU associated with an aluminium alkyl co-catalyst in a 1 1 molar ratio, polymerizes butadiene, but it is also able to afford cyclododecatriene provided that the TiCU/co-catalyst molar ratio is kept approximately to 0.1 instead of 1 [M. Rapoport and D. L. Sullivan, Can. Patent 1 055 052 (1979), to DuPont]. Although the mechanism is unclear, this is a good example of how delicate can be the modulation of a catalytic system for a selective synthesis. 

Morini, G. Cristofori, A. Diethers Suitable for Use in the Preparation of Ziegler-Natta Catalysts. Eur. Patent 728,724, February 21, 1996. 

Ziegler-Natta catalysts can polymerize a variety of structurally different monomers. Examples of stereoregular homopolymers (Table IV), elastomeric or crystalline copolymers, as well as block copolymers may be found in the patent and open literature (, 49-51). Ethylene polymerizes easily with many soluble and heterogeneous Ziegler catalysts. Some ethylene-active catalysts, for example, Cp2TiCl2 + aluminum alkyl (52). are not active for a-olefin polymerizations. However, all known Ziegler catalysts that polymerize propylene are also active in ethylene polymerization. 

After 30 years, olefin polymerization by a coordinated anionic mechanism continues to receive worldwide attention as evidenced by a voluminous patent and journal literature. Much attention has been directed to catalyst and process optimization and understanding of key reaction variables. The development of high-activity Ziegler-Natta catalysts has spurred a renewed interest in simplified processes requiring no post-treatment of the polymers. Recent announcements by Union Carbide of a low-pressure, fluid bed... 

Other kinds of coordination catalytic systems developed few years before the Ziegler-Natta catalysts were based on chromium and molybdenum oxides supported on SiOj AI2O3 and other supports. The catalysts were patented by Phillips Petroleum and Standard Oil companies of Indiana for the synthesis of polyolefins. Although Phillips catalysts were the first to produce a fraction of crystalline polypropylene, these systems were more useful for the production of polyethylene. In fact, the Phillips and the Ziegler-Natta catalysts are currently the two commercial systems that dominate the production of HDPE [2]. 

The effectiveness of Ziegler-Natta catalysts of the triethylaluminum-titanium tetrachloride type seems to be the subject of some controversy. One patent describes the formation of poly(vinyl fluoride) with such a catalytic system in THF in a bottle polymerization at 30 C and autogenous pressure for 6 hr [57]. A complex of triisobutylaluminum, vanadium oxytrichloride, and THF is said to be particularly effective at 30°C both for the homo- and copolymerizations of vinyl fluoride [58, 59]. The processes are said to resemble typical Ziegler-Natta systems and are independent of the THF concentration when the mole ratio of THF to VOCI3 was greater than 2.3 1. The use of triisobutylaluminum with tetraisopropoxytitanium at 30°C for 15 min is said to lead to a process with an ionic-coordination mechanism [60]. 

Fig. 6.2 Commercial flow reactor for slurry polymerization of ethylene with Ziegler-Natta catalysts as illustrated in a British patent 826 523...

A most famous metal-based initiator is the Ziegler-Natta catalyst, which is made from a titanium-based catalyst and an electron-deficient A1(C2H5)3 cocatalyst. Since this used to be patented, naturally, there are now many Ziegler-Natta-type catalysts based on different metals. The Ziegler-Natta process is used today to produce poly alkene plastics and elastomers, which are produced on a scale of over 100 million tons a year. Karl Ziegler and Giulio Natta (Figure 6.2) were awarded the Nobel Prize in Chemistry in 1963 for their invention, which altered our world for better and for worse. 

The pre-eminent interest in lanthanides for the polymerization and copolymerization of conjugated diolefins is demonstrated by a large scientific and patent literature. A recent paper by one of us (24) reviewed the main worldwide contributions on butadiene and isoprene polymerization. Very recent contributions in this field come from Hsieh and Yeh (25). They observed that the butadiene polymerization in n-pentane evolves as a slurry process, the cis-polybutadiene being insoluble in the light hydrocarbon. They also measured a lower activation energy for Nd-based than for conventional Ziegler-Natta catalysts foi- both butadiene and isoprene polymerization. 

Sita, L. R. Jayaratne, K. C. Stereospecific living polymerization of olefins by a novel Ziegler-Natta catalyst composition. U.S. Patent 6,579,998 B2 (University of Maryland), June 17, 2003. 

Boron alkyls and Ziegler-Natta catalyst systems have also been mentioned in the patent literature [551,552]. The initiating systems have been modified by the addition of elemental titanium, solvents (lactones, amides), plasticizers (esters, carboxylic or phosphoric acids), and lead and cadmium compounds. 

The imique properties of i-PP produced with ansa-metallocene catalysts, including their low content of easily migrating short-chain polymer, desirable in particular for food and medical packaging and related purposes [72], has driven the industrial use of i-PP produced with ansa-metallocene catalysts in some demanding market sectors. However, higher costs, the dominance of homo-polypropylene, improved Ziegler-Natta catalysts and, last but not least, a complicated patent situation have as of today restricted their use in the i-PP field to specialized niche applications. 

Alkoxy silanes are cited as external donors in a large number of recent patents for Ziegler-Natta catalyst systems.The advantages of these donors becsune known in the early 80 s. O) Before the silanes, other types of Lewis bases, like aromatic esters or bulky amines, were used as external donors. 

A large number of papers and patents on Ziegler-Natta catalysts... 

From these data it appears evident that conventional Ziegler-Natta catalysts can be considered as a mature technology and less research is now done in this field. However they still represent a very important percentage of the total amount of filed patent applications, confirming the opinion that the decline of polyolefins produced by conventional ZN catalysts will be slow and probably not complete. 

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