Ring-Opening-Metathesis Polymerizations

Ring-opening metathesis polymerization of cycloolefins,93-99 a reaction of significant practical importance (see Section 12.3), is catalyzed by a number of well-defined transition-metal complexes. Alkylidene and metallacyclobutane 

Whereas only limited stereoselectivity is characteristic of the metathesis of acyclic olefins, ring-opening metathesis polymerization of cycloalkenes may be highly stereoselective provided the proper catalysts and reaction conditions are selected. Cyclopentene, for instance, is transformed to either all-cis [Eq. (12.25)] or all-frans polypentenamers [Eq. (12.26)] in the presence of tungsten catalysts 21 92 

Because of its favorable kinetic and thermodynamic properties, norbomene can be polymerized with simple transition-metal halogenides.99 116 Even RuC13, which is not active in other metathesis reactions, is effective in the ring-opening polymerization of norbomene.117118 Developments in the early 1990s include the use of 

Ring opening of norbomene by Mo, W, Re, Os, Ru, and Ir compounds taking place at the double bond results in polymers with a complete range of cis/trans character, but the cyclopentane rings are always cis-1,3 enchained  

Much less is known about the ring-opening polymerization of norbomadiene. Surprisingly, OSCI3, a nonselective catalyst in the polymerization of norbomene, was found to yield an all-cis polymer.121 

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. 

A few years ago, an excellent compilation of all aspects of metathesis chemistry, including those of ring-opening metathesis polymerization (ROMP), was edited by R. H. Grubbs [1]. In this chapter, the basic principles of ROMP-as well as the particular features of the most important initiators relevant to ROMP-are outlined. In view of the quite comprehensive set of data reported in the above-mentioned book, and the limitations in space in this chapter, only the latest relevant developments in ROMP will be summarized at this point. 

Introduction to Ring-Opening Metathesis Polymerization (ROMP) 

Handbook of Ring-Opening Polymerization. Edited by P. Dubois, 0. Coulembier, and. -M. Raquez Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31953-4 

The extent of this process depends heavily on temperature, monomer concentration, the cisjtrans configuration of the double bonds within the polymer backbone. 

Originally, the conversion of substituted bicyclo[2.2.2]octa-2,5-dienes into a precursor polymer of PPVs by ring opening metathesis polymerization (ROMP) has been shown by Grubbs using a molybdenum-based metathesis catalyst. The precursor polymer aromatizes in an inert atmosphere at 280 0, or in the presence of trioctylamine at 200°C. 

Related to ROMP is the acyclic diene metathesis (ADMET) procedure. Here, the starting monomer is a substituted p-divinylbenzene. During the polymerization, ethene is ejected. However, only low-molecular-weight polymers can be obtained by ADMET. 

ROMP is a powerful technique for the preparation of polymers with high molecular weights and low dispersity [38]. A number of computational studies on ROMP with various olefin substrates have been reported. For example, a direct comparison of the computed energies of the intermediates and transition states in the ROMP of norbornene, cyclopentene, cycloheptene, and Z-cyclooctene was reported by Cramer and Hillmyer [39] in 2012 (Table 7.1). In these reactions, a fused bicyclic metallacylobutane intermediate is formed, and the ring strain 

The reaction of norbornene was also found to have a lower activation barrier to form the metallacyclobutane than the reactions of cyclopentene, cycloheptene, and Z-cyclooctene. This can be attributed to the pre-distorted double bond of norbornene, which requires less distortion to achieve the pyramidalized geometry in the transition state than that needed for planar olefins [43]. 

1 The catalyst remains bonded to the new alkene formed from the cyclic alkene. 

2 The driving force for the reaction is relief of the ring strain and the reaction is therefore irreversible and only works for strained alkenes. 

The best results, in terms of catalyst recycling, were obtained when toluene was used as a co-solvent with the ionic liquid. Without toluene, the yield of polymer produced decreases dramatically to only 10% in the third cycle compared to 98 % in the first. 

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

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). 

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). 

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)...

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... 

Ionic, Ziegler-Natta and Ring-Opening Metathesis Polymerization By V. Dragiitan and R. Streck... 

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

RING-OPENING METATHESIS POLYMERIZATION OF CYCLIC ALKENES... 

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