Polymerization metal catalysed

In contrast to the free-radical polymerizations, there have been relatively few studies on transition metal catalysed polymerization reactions in water. This is largely due to the fact that the early transition metal catalysts used commercially for the polymerization of olefins tend to be very water-sensitive. However, with the development of late transition metal catalysts for olefin polymerizations, water is beginning to be exploited as a medium for this type of polymerization reaction. For example, cationic Pd(II)-bisphosphine complexes have been found to be active catalysts for olefin-CO copolymerization [21]. Solubility of the catalyst in water is achieved by using a sulfonated phosphine ligand (Figure 10.5) as described in Chapter 5. 

Many other metal-catalysed polymerizations may be carried out in water including the copper-catalysed polymerization of methacrylates, the palladium-and nickel-catalysed polymerization of ethene and other alkenes and the rhodium-catalysed polymerization of butadiene [22],... 

Transition metal catalysed precipitation polymerization utilizes the advances in the development of suitable catalysts for homogeneous reactions in SCCO2. For example, the synthesis of poly(phenyl acetylene) may been achieved using a... 

One of the characteristic features of the metal-catalysed reaction of acetylene with hydrogen is that, in addition to ethylene and ethane, hydrocarbons containing more than two carbon atoms are frequently observed in appreciable yields. The hydropolymerisation of acetylene over nickel—pumice catalysts was investigated in some detail by Sheridan [169] who found that, between 200 and 250°C, extensive polymerisation to yield predominantly C4 - and C6 -polymers occurred, although small amounts of all polymers up to Cn, where n > 31, were also observed. It was also shown that the polymeric products were aliphatic hydrocarbons, although subsequent studies with nickel—alumina [176] revealed that, whilst the main products were aliphatic hydrocarbons, small amounts of cyclohexene, cyclohexane and aromatic hydrocarbons were also formed. The extent of polymerisation appears to be greater with the first row metals, iron, cobalt, nickel and copper, where up to 60% of the acetylene may polymerise, than with the second and third row noble Group VIII metals. With alumina-supported noble metals, the polymerisation prod-... 

The alkene metathesis reaction arose serendipitously from the exploration of transition-metal-catalysed alkene polymerisation. Due to the complexity of the polymeric products, the metathetic nature of the reaction seems to have been overlooked in early reports. However, in 1964, Banks and Bailey reported on what was described as the olefin disproportionation of acyclic alkenes where exchange was evident due to the monomeric nature of the products [8]. The reaction was actually a combination of isomerisation and metathesis, leading to complex mixtures, but by 1966 Calderon and co-workers had reported on the preparation of a homogeneous W/Al-based catalyst system that effected extraordinarily rapid alkylidene... 

R = Ph, tt-Bu, tt-Pen, tt-Hex SCHEME 27. Transition metal-catalysed addition-polymerization of germylenes to acetylenes... 

The first drawback in the use of water (the solubility problem) may be overcome by using surfactants, which solubilize organic materials or form emulsions with them in water. Indeed, surfactants have been occasionally used in organic synthesis [3-6]. A successful example is emulsion polymerization [7]. Some late transition metal-catalysed reactions in water have also been conducted in the presence of surfactants or surfactantlike ligands [8-15]. In many other cases, however, large quantities of surfactant molecules compared with the reaction substrates are needed for the desired reactions to proceed efficiently, and thus, the systems are impractical even if water can be used as a solvent. From the viewpoints of practicability and applicability, the surfactant-aided organic synthesis is still at the preliminary stage. 

After polymerization processes, one of the most important aqueous phase reactions to be performed on an industrial scale is the Rhone-Poulenc hydro-formylation process that utilizes a water soluble rhodium phosphine catalyst. This process will be discussed in more detail in Chapter 10. The success of this process has led to many exciting results in metal catalysed aqueous phase chemistry. Additionally, amazing advances have been made where reactions that are typically considered unsuited to the presence of moisture, e.g. Grignard-type chemistry, can be performed in water. 

Zambelli, A., Sacchi, M. C., Locatelli, P. Intemat. Symposium on Transition metal catalysed polymerizations unsolved problems . Midland, August 1981... 

Structures 25.55 (Grubbs catalyst) and 25.56 (a complex developed by Schrock) show two important carbene compounds that are used as catalysts in alkene olefin) metathesis, i.e. metal-catalysed reactions in which C=C bonds are redistributed. Examples include ring-opening metathesis polymerization (ROMP) and ring-closing metathesis (RCM). We look at these reactions in detail in Section 26.3. 

However the material obtained was an unprocessable powder. Unlike substituted polyacetylenes, polyacetylene is insoluble, infusible and unstable in air. The discovery of a technique to synthesize the polymer in the form of a free-standing film and the use of electron donors and acceptors to dope it to have metallic conductivity produced intense interest in the polymer in the last two decades. A wide variety of catalyst systems has been described for the polymerization of acetylene. Besides the route via acetylene polymerization, polyacetylene can also be obtained by a two-step route which involves the synthesis of soluble polymer precursors, which are converted to polyacetylene via thermal elimination and transition-metal-catalysed isomerization, as well as by polymerization of cyclooctatetraene , by dehydrochlorination of poly(vinyl chloride) and by dehydration of poly(vinyl alcohol)... 

R 118 M. Kang, A. Sen, L. Zakharov and A.L. Rheingold, Trends in Alkene Insertion in Late- and Early-Transition Metal Compounds Relevance to Transition Metal-Catalysed Polymerization of Polar Vinyl Monomers , p. 143... 

Quirk, R.P., Ed., Transition Metal Catalysed Polymerizations, Harwood Academic Press, 1983. Stevens, M., Polymer Chemistry An Introduction, 3rd ed., Oxford University Press, 1998. 

Generally speakiiig. transition metal catalysed polymerizaticHi cannot be performed in aqueous media since water destroys active catalyst complexes. However, there are a few monomers whidi have been ptdymerized in pure wat - via transition metal catalyzed reactions. The following discussion of these polymerizations have been divided into vinyl polymerizations and ring-opening metatiiesis polymerizations (ROMP). 

Other metal-catalysed Oligomerization of C2H4 Polymerization of C2H4 AlEt3 Ni(0) complexes Supported chromium (II) oxide supported Ziegler... 

Kissin, V. V, in Proc. Symp. on Transition Metal Catalysed polymerization the Ziegler-Natta and Metathesis Polymerization, Cambridge University Press, New York, 1988. Alderson, T., Ruthenium chloride as catalyst in ethylene dimerization reaction,/. Amer Chem. Soc., 87, 5638, 1965. 

Table 3 Athene and alkyne oligomerization and polymerization reactions catalysed by transition-metal compounds 1... 

---