Metal catalysts, polymerizations using

Transition metal catalysts are useful for the polymerization of acetylenes. Ti catalysts are known to polymerize acetylene. Catalysts containing group V and VI transition metals (i.e., Nb, Ta, Mo, and W) polymerize substituted acetylenes (3, 4). The group V and VI transition metal catalysts can be classified into three groups (1) chlorides of Nb, Ta, Mo, and W (2) 1 1 mixtures of the metal chlorides with organometallic cocatalysts (e.g.. 

As previously mentioned, in addition to free radical initiation, ethylene may be polymerized by use of transition metal catalysts. To place the importance of these catalysts in proper perspective, one must recognize that transition metal catalysts were used to produce about 73% of the global industrial output of polyethylenes in 2008 or about 56 million tons (124 billion pounds). 

The ethynyl groups of ethynylbenzenes undergo polymerization by the action of Group 6, 7, and 9 transition metal catalysts, often used for olefin metathesis, to give the corresponding polyenes which are frequently called poly(phenylacetylene)s (43) [15, 47]. 

The use of fluidized beds for gas-phase polymerization started in 1968 with the UNIPOL process, which was developed by Union Carbide to make high-density polyethylene. This process has now been adapted to produce other grades of polyethylene as well as polypropylene and various copolymers. The fluid bed is composed of porous particles, which are aggregates of polymer containing fine grains of titanium, chromium, or other metal catalyst. Polymerization takes place at the polymer-catalyst interface, and the particles grow larger over a period of several hours. Some of the polymer is withdrawn continuously or at intervals to maintain the bed... 

Ohgomerization reactions involve mono-olefins and dienes polymerization reactions are mechanistically similar. Polymerization or copolymerization with soluble or insoluble transition metal catalysts is used to produce ... 

Polypropylene (PP) is another common plastic used extensively in packaging apphca-tions. Its homopolymer is produced by catalytic addition polymerization of propylene. In the case of PP copolymer, a co-monomer such as ethylene is also used. An organo-metallic catalyst is used, which attaches to propylene, works as functional group and reacts with the unsaturated bond of propylene (or with other co-monomer in case of copolymerization) to form a long chain polymer (Maier and Calafirt, 1998). 

An additional advantage of LDPE resins is that no heavy metal catalysts are used for the polymerization, and therefore stabilization with antioxidants is not required. This feature makes LDPE a candidate for pharmaceutical applications, such as infusion bottles made by the BPS (blown-fill seal) process. The worldwide market trend in this application is the use of higher density LDPEs, since in most BPS production lines... 

Others. Oxahc acid is used for the production of cobalt, as a raw material of various agrochemicals and pharmaceuticals, for the manufacture of electronic materials (76—83), for the extraction of tungsten from ore (84), for the production of metal catalysts (85,86), as a polymerization initiator (87—89), and for the manufacture of zirconium (90) and beryhium oxide (91). 

These siUca-supported catalysts demonstrate the close connections between catalysis in solutions and catalysis on surfaces, but they are not industrial catalysts. However, siUca is used as a support for chromium complexes, formed either from chromocene or chromium salts, that are industrial catalysts for polymerization of a-olefins (64,65). Supported chromium complex catalysts are used on an enormous scale in the manufacture of linear polyethylene in the Unipol and Phillips processes (see Olefin polymers). The exact stmctures of the surface species are still not known, but it is evident that there is a close analogy linking soluble and supported metal complex catalysts for olefin polymerization. 

The discovery by Ziegler that ethylene and propylene can be polymerized with transition-metal salts reduced with trialkyl aluminum gave impetus to investigations of the polymerization of conjugated dienes (7—9). In 1955, synthetic polyisoprene (90—97% tij -l,4) was prepared using two new catalysts. A transition-metal catalyst was developed at B. E. Goodrich (10) and an alkaU metal catalyst was developed at the Ekestone Tke Rubber Co. (11). Both catalysts were used to prepare tij -l,4-polyisoprene on a commercial scale (9—19). 

When a mixture of alkenes 1 and 2 or an unsymmetrically substituted alkene 3 is treated with an appropriate transition-metal catalyst, a mixture of products (including fi/Z-isomers) from apparent interchange of alkylidene moieties is obtained by a process called alkene metathesis. With the development of new catalysts in recent years, alkene metathesis has become a useful synthetic method. Special synthetic applications are, for example, ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROM) (see below). 

The previous sections show that certain ionic liquids, namely the chloroalumi-nate(III) ionic liquids, are capable of acting both as catalyst and as solvent for the polymerization of certain olefins, although in a somewhat uncontrolled manner, and that other ionic liquids, namely the non-chloroaluminate(III) ionic liquids, are capable of acting as solvents for free radical polymerization processes. In attempts to carry out polymerization reactions in a more controlled manner, several studies have used dissolved transition metal catalysts in ambient-temperature ionic liquids and have investigated the compatibility of the catalyst towards a range of polymerization systems. 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Transition metal coupling polymerization has also been used to synthesize optically active polymers with stable main-chain chirality such as polymers 33, 34, 35, and 36 by using optically active monomers.29-31 These polymers are useful for chiral separation and asymmetric catalysis. For example, polymers 33 and 34 have been used as polymeric chiral catalysts for asymmetric catalysis. Due... 

Development of more efficient transition metal catalyst systems including using novel and efficient ligands has been one of the focuses in organometallic chemistry.35 The developments in this area will allow not only to synthesize polymers under mild conditions with higher or desired molecular weights but also to use less expensive, more readily available materials for the polymerizations. 

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

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