Coordinative polymerization, discovery

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

The most important representatives are the lowest 1-alkenes, ethylene and propene. Ethylene is not particularly easily polymerized by radical or ionic mechanisms. Its importance as a monomer was greatly enhanced by the discovery of coordination polymerizations. Propene is oligomerized by radical and ionic initiators. This explains the importance of Natta s modification [1] of Ziegler [2,3] catalysts, enabling inferior raw materials to yield high-quality polymers. 

On the other hand, a certain dose of creative spirit is appropriate. When the requirements of modem research methods are respected, good reproducibility can be achieved, disturbing effects can be limited, and our knowledge can be promoted by a further step. The measured constants, even though only defined for a certain system, form an excellent basis for further discoveries. The values of propagation rate constants for some monomers in radical, ionic and coordination polymerizations are summarized in Table 9. 

A quarter of a century after the discovery of coordination polymerizations, in spite of tens of highly qualified and hundreds of supplementary studies, and millions of tons of polyalkenes produced each year, we still must confess that we possess only very general ideas about the basic kinetic features of these reactions. 

Since the discovery of coordination catalysts based on various metal alkoxides (Fe, Zn, Al), such catalysts have proved of great value for the preparation of high-molecular-weight polymers. Many studies have been devoted to coordination polymerization, but the mechanism has not yet been fully elucidated. Depending on the type of the catalyst and the metal employed, we can speak of coordinate cationic and coordinate anionic processes. 

Until 1953, almost all vinyl polymerization of commercial importance was of the free-radical type. Since that time, however, ionic polymerization, chiefly in the form of coordination polymerization, has revolutionized the field. Following discoveries by Karl Ziegler (of the Max Planck Institute for Coal Research) and by Guilio Natta (of the Polytechnic Institute of Milan)—who jointly received the Nobel Prize in 1963 for this work—catalysts have been developed that permit control of the polymerization process to a degree never before possible. 

Lanthanides, which are d-electron deficient metals similar to early transition metals such as Ti and Zr, polymerize ethylene and acrylic esters. Although studies of coordination polymerization of 1,3-butadiene catalyzed by lanthanide compounds started as early as 1964 by discovery of the Ce catalysts... 

Give an example of coordination polymerization. Name the chemists reponsible for the discovery of this method of polymerization. 

Polymers are macromolecules which are composed of smaller molecules linked by covalent bonds. In terms of the reaction kinetics, polymerizations are traditionally classified into several categories stepwise polymerization, free-radical polymerization, ionic polymerization, ring-open polymerization, and coordination polymerization or polyinsertion. Each polymerization method has a combination of requirements for reaction conditions, and they exhibit certain types of product and process features (Caneba, 1992a, 1992b Odian, 1991). Even though in principle, the FRRPP process can be implemented with a wide variety of polymerization mechanisms, its discovery and immediate implementation has occurred in conjunction with free-radical kinetics. 

The Introduction gives a historical overview of SPS from the first discovery through developmental stages to the fuU commercialization of this polymer based on an inexpensive monomer (Chapter 1). Because the transition metal catalysts for the coordination polymerization of styrene are of high importance for the properties of the polymers, these catalysts are comprehensively covered in the section on the preparation of SPS. 

The discovery of coordinate polymerization of oxirane led to an enormous expansion in the range of polyether structures that could be synthesized. Some of the remarkable synthesis chemistry is outlined in Section III. Coordinate copolymerization further increased the range of polymer structures that could be synthesized in highly controlled ways. Two examples have already been described copolymers of epichlorohydrin and ethylene oxide (71) and of propylene oxide and allyl glycidyl ether (94, 137). The activation energy for copolymerization of epichlorohydrin and maleic anhydride was found to be 14.5 kcal/mol, and the polymerization rate is dependent on temperature and proportional to catalyst concentration (138-140). 

The coordination polymerization is a new type of synthesis of macromo-lecular compounds to obtain polymers with a regular spatial structure. It was preceded by the basic researchs presented in the field of synthesis and application of organometalhc compounds. The studies have led in 1953 to the discovery of a new complexing compound consisting of triethylalu-minium and titanium trichloride. 

The strong interest of industry for Ziegler - Natta catalysts led to the discovery of new types of bonds of diverse, often much more active and applicable for different purposes forms. Currently catalytic systems operating in a homogenous as well as a heterogeneous environment system are known. They allow to make the coordination polymerization in solution or in a fluidized phase. 

The next major commodity plastic worth discussing is polypropylene. Polypropylene is a thermoplastic, crystalline resin. Its production technology is based on Ziegler s discovery in 1953 of metal alkyl-transition metal halide olefin polymerization catalysts. These are heterogeneous coordination systems that produce resin by stereo specific polymerization of propylene. Stereoregular polymers characteristically have monomeric units arranged in orderly periodic steric configuration. 

The significance of this discovery is that control of the degree of polymerization and of coordination modes of the thiolate precursors is hkely to affect the shape of the final nanoproduct in a solventless method. Since traditional thiol-metal coordination chemistry is well established, this affords a great opportunity to join the traditional coordination chemistry with an increased variety of nano-... 

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