Polymerization, metathesis

Metathesis polymerization has become an important tool for polymer synthesis and has even attracted a Nobel Prize [46-49]. Acyclic diene molecules are capable of undergoing intramolecular and intermolecular reactions in the presence of appropriate transition metal catalysts, for example, molybdenum alkylidene and ruthenium carbene complexes. The intramolecular reaction, called ring-closing olefin metathesis (RCM), leads to cyclic compounds and the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, leads to oligomers and polymers. Altering the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

Gurtler and Jautelat of Bayer AG have protected methods that use chloroalu-minate(iii) ionic liquids as solvents for both cyclization and polymerization reactions of acyclic dienes [50]. They employed the neutral ionic liquid [EMIMjCl-TUQs (X(A1Q3) = 0.5) to immobilize a mthenium carbene complex for biphasic ADMET polymerization of an acyclic diene ester. Fig. 7-2. The reaction is an equilibrium process, therefore, removal of ethylene drives the equilibrium to products. The reaction proceeds readily at ambient temperatures producing mostly polymeric materials but also 10% dimeric material. 

Olefin (or alkene) metathesis is a disproportionation reaction which may be represented generally by 

Metathesis polymerization is similar to Ziegler-Natta polymerization in that it is catalysed by the products of reactions between transition metal compounds and either metal alkyls or Lewis acids. However, in contrast to 

The active species in propagation is a transition metal carbene with a vacant d-orbital. For polymerization of cyclopentene by tungsten-based catalysts the overall propagation reaction can be represented by 

Thus the ring-opening reaction proceeds by cleavage of the C=C bond in the monomer. 

Whilst metathesis polymerization has been known since the mid-1950s it is only during the last decade that it has been extensively studied. It has been used in a convenient route for the synthesis of inherently conductive polyacetylene and is used commercially to prepare polymers from norbornene 

Such reactions of cycloolefins are called metathesis polymerization by analogy with the transalkylidenation reaction of linear olefins which proceed under comparable conditions and in which the double bonds of the olefins are broken and new double bonds are formed (metathesis)  

In the polymerization of cycloalkenes, not only linear polymers, but also cyclic oligomers are formed. These reactions are thus examples of ring/chain equilibriums, but their mechanism is not yet fully clarified. 

Polyd-Pentenylene) by Metathesis Polymerization of Cyclopentenewith a Ziegler-Natta-Catalyst In Solution 

Safety precautions More this experiment is carried out, Sect. 2.2.5 must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. 

Cfluf/on. Aluminum alkyls must be handled under total exclusion of oxygen and moisture (see Example 3-28). 

Giirtler and Jautelat of Bayer AG have protected methods that use chloroalumi-nate(III) ionic liquids as solvents for both cycHzation and polymerization reactions of acyclic dienes [52]. They employed the neutral ionic liquid [EMIM][Cl-AlCl3] 

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AQUACULTURECHEMICALS] (Vol3) ROMP. See Ring-opening metathesis polymerization... 

Cyclic Polyolefins (GPO) and Gycloolefin Copolymers (GOG). Japanese and European companies are developing amorphous cycHc polyolefins as substrate materials for optical data storage (213—217). The materials are based on dicyclopentadiene and/or tetracyclododecene (10), where R = H, alkyl, or COOCH. Products are formed by Ziegler-Natta polymerization with addition of ethylene or propylene (11) or so-called metathesis polymerization and hydrogenation (12), (101,216). These products may stiU contain about 10% of the dicycHc stmcture (216). 

The production of CPO is based on relatively inexpensive cycHc substances these must be derivatized, however, to meet the requirements of resistance to heat softening and suitabiUty for metallization. Metathesis polymerization is problem-prone, since relatively large amounts of catalyst (WCl, C2H AlCl2) must be removed by solvent extraction (216). In the process, the price of CPO, at small batches, is several times higher than that of BPA-PC. 

Aqueous ring-opening metathesis polymerization (ROMP) was first described in 1989 (90) and it has been appHed to maleic anhydride (91). Furan [110-00-9] reacts in a Diels-Alder reaction with maleic anhydride to give exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3—dicarboxylate anhydride [6118-51 -0] (24). The condensed product is treated with a soluble mthenium(Ill) [7440-18-8] catalyst in water to give upon acidification the polymer (25). Several apphcations for this new copolymer have been suggested (91). 

Ring-Opening Metathesis Polymerization. Several new titanacyclobutanes have been shown to initiate living ring-opening metathesis polymerization (ROMP) systems. These have been used to make diblock and triblock copolymers of norbomene [498-66-8] (N) and its derivatives (eg, dicyclopentadiene [77-73-6] (D)) (Fig. 2) (41). 

Poly(dicyclopentadiene). The development of polydicyclopentadiene [25038-78-2] for reaction injection molding is an area which has generated much interest. The polyDCPD is obtained via metathesis polymerization of high purity (usually greater than 98%) DCPD. Excellent reviews (61—62) of the chemistry and properties of polyDCPD have been pubHshed. The patent Hterature of polyDCPD synthesis, catalysts, modifiers, and appHcations is dominated by Hercules (44 patents) and B. F. Goodrich (43 patents) in the U.S. Other participants are Orkem, SheU, Nippon Zeon, and Teijin. 

A drawback to the Durham method for the synthesis of polyacetylene is the necessity of elimination of a relatively large molecule during conversion. This can be overcome by the inclusion of strained rings into the precursor polymer stmcture. This technique was developed in the investigation of the ring-opening metathesis polymerization (ROMP) of benzvalene as shown in equation 3 (31). 

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). 

Another metathesis polymerization procedure uses terminal dienes such as hexa-1,5-diene (16) (acyclic diene metathesis (ADMET)). Here again, the escape of the gaseous reaction product, i.e. ethylene, ensures the irreversible progress of the reaction ... 

K. J. Ivin, J. C. Mol, Olefin Metathesis and Metathesis Polymerization, Academic Press, London, 1997. 

Figure 7.4-2 Acyclic diene metathesis polymerization (ADMET) reaction carried out in the...

A potential drawback of all the routes discussed thus far is that there is little control over polydispersity and molecular weight of the resultant polymer. Ringopening metathesis polymerization (ROMP) is a living polymerization method and, in theory, affords materials with low polydispersities and predictable molecular weights. This methodology has been applied to the synthesis of polyacctylcne by Feast [23], and has recently been exploited in the synthesis of PPV. Bicyclic monomer 12 [24] and cyclophane 13 [25) afford well-defined precursor polymers which may be converted into PPV 1 by thermal elimination as described in Scheme 1-4. 

Ring-opening metathesis polymerization (ROMP) of 1,4-cyelooctadiene was used to prepare poly(l,4-B) terminated with halo end groups.647 This was then used as a macroinitiator of ATRP with heterogeneous Cu bpy catalysts to form PS- >/ti /r-poly(l,4-B)-WoeA -PS and PMMA-Moc.T-poly(l,4-B)-Wof A-PMMA. 

Scheme 2 Different modes of the olefin metathesis reaction cross metathesis (CM), ringclosing metathesis (RCM), ring-opening metathesis (ROM), acyclic diene metathesis polymerization (ADMET), and ring-opening metathesis polymerization (ROMP)...

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. 

At this point it is appropriate to discuss the mechanism for ADMET, because ADMET polymerization is more involved than its chain polymerization counterpart— ROMP. Figure 8.6 illustrates the accepted mechanistic pathway which leads to productive metathesis polymerization, as first described by Wagener et al.14a A general model reaction between an a,o>-diene with a metal alkylidene... 

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... 

The polynorbornenes X bearing cyclotriphosphazenes with -0(CH2CH20)x-CH3 (x=l, 2,3,7.2) side groups have been prepared via ring opening metathesis polymerization (ROMP) and complexed with LiS03Cp3 and LiN(S02Cp3)2 (10-60% molar ratios) by Allcock [619,620]. 

Lu H, Wang J, Lin Y, Oieng J (2009) One-pot synthesis of brush-like polymers via integrated ring-opening metathesis polymerization and polymerization of amino acid N-carboxyanhy-drides. J Am Oiem Soc 131 13582-13583... 

Brzezinska KR, Deming TJ (2001) Synthesis of ABA triblock copolymers via acyclic diene metathesis polymerization and living polymerization of alpha-amino acid-N-carboxyanhy-drides. Macromolecules 34 4348 354... 

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