Polymerizations metathesis type

Polymerization of acetylenes by metathesis-type catalysts such as M0CI5 and WCle/PluSn was first observed in the 1970s (Woon 1974 Masuda 1974, 1976), but the nature of the chain carrier was then in some doubt. However, it was soon found (i) that metal carbene complexes would initiate the polymerization of MesCC=CH at 60°C (Katz 1980a) (ii) that end-groups derived from such initiators could be detected in polymers of PhC=CH (Kunzler 1988b) and (iii) that triblock copolymers could be made by successive addition of norbomene, acetylene and norbomene to such initiators (Schlund 1989). All types of acetylene can be polymerized in this way and the reactions proceed by a ROMP-type mechanism see Ch. 10. 

Metathesis-type reactions of acetylenes fall into two categories true metathesis, in which the triple bond is completely broken, and olefin-type metathesis, in which only two of the three bonds are broken. The latter results in polymerization and the formation of cyclic oligomers, especially trimers. The overall reactions are illustrated by eqns. (l)- 3). 

Cossee type. The mechanism comprised of olefin metathesis type elementary processes involving a metal carhene complex and a metallacyclobutane was established only recently after the development of the chemistry of metal-carbene complexes [129], Understanding of the novel kind of reaction mechanism opened a new horizon in polymerization. Various new types of polymerization of cyclic monomers have been realized by ROMP. An advantage of the process is that the processes are tolerant to polar reactants and solvents enabling ready incorporation of polar substituents into polymers. Another advantage is that the ROMP is living in nature and polymers of narrow molecular weight distributions are available by the method. 

The debate on the mechanism of polymerization, whether an insertion mechanism (Cossee-Arlman) [6], or a metathesis-type mechanism initiated by a-H elimination from the alkyl complex to give a hydrido-carbene intermediate (Green-Rooney) [108], was solved in favor of the former on the basis of the absence of isotope effect on the rates of insertion, and on the stereochemistry of alkene intramolecular insertion, when a-D alkyls were used in the cyclizafion reaction shown in Eq. 6.21 [109]. 

There is a close identity between the catalysts that cause the Ziegler-Natta-type polymerizations and those that cause metathesis-type polymerization via a carbene mechanism (see Chapter 4). 

On the other hand, metathesis-type polymerization of norbomene takes place with WCL6-[(C2Hs)3A1] 1.5 or WCl6-(CH3)4Sn to yield ... 

Metathesis type catalysts can also polymerize substituted acetylenes. This is discussed in Chap. 10. 

Describe living metathesis polymerization. What types of catalysts are useful in such polymeriz ations ... 

Living metathesis type polymerization was also employed to form block copolymers from norbornene and its derivative with bimetallic ruthenium catalysts, (PR3)2Cl2Ru(=CH-p-C6H4CH=) RuCl2(PR3)2 [434], This can be illustrated as follows [434] ... 

This catalyst, however, turned out to be considerably less active in ring opening metathesis polymerization of norbom-2-ene and in metathesis polymerization of c/s-2-pentene. Better results were obtained when a ruthenium-based metathesis type catalyst was immobilized via an A -heterocy-clic carbene [57]. Additional improvements in performance were obtained when the catalyst was immobilized on a monolithic silica rods ... 

WeU-defined carbene catalysts show excellent activity for polymerization, and are isolable and thus informative to suppose the polymerization mechanism as metathesis type. The first example of isolated single-component carbene catalysts is Kscher and Casey carbenes (1 and 2, respectively. Figure 1), which polymerize PA, tert-butylacetylene, and cyclooctyne in... 

A type of ring opening addition polymerization using transition metal catalysts not unlike Ziegler-Natta catalysts is called metathesis polymerization." Metathesis polymers, first made in the 1960s, are called polyalkenamers. Polymers made from cyclooctadiene and norbornadiene have applications as specialty elastomers. The polymerization of norbornadiene can be summarized as follows ... 

Olefin metathesis, an expression coined by Calderon in 1967,1 has been accurately described in Ivin and Mol s seminal text Olefin Metathesis and Metathesis Polymerization as the (apparent) interchange of carbon atoms between a pair of double bonds (ref. 2, p. 1). This remarkable conversion can be divided into three types of reactions, as illustrated in Fig. 8.1. These reactions have been used extensively in the synthesis of a broad range of both macromolecules and small molecules3 this chapter focuses on acyclic diene metathesis (ADMET) polymerization as a versatile route for the production of a wide range of functionalized polymers. 

Metathesis chemistry, histoiy of, 431-432 Metathesis depolymerization, 456-457 Metathesis polymerization, general conditions for, 440-441 Metathesis reactions, types of, 432 Methanol, 377 Methanolysis, 535... 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

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