Norbomene polymerization

I. Tritto, L. Boggioni, and D.R. Ferro, Metallocene catalyzed ethene-and propene co-norbomene polymerization Mechanisms from a de-... 

Some cycloolefins can undergo either a regular cationic polymerization or a metathesis one, depending upon the catalyst. One of them is norbomene and its derivatives. For instance, 5-methylene-2-norbomene polymerizes by a cationic mechanism with a 1 1 combination of tungsten hexachloride with tetraalkyltin. A 1 4 combination of a tungsten halide with either C2H5AICI2, or... 

The rate of norbomene polymerization is first order in catalyst and first order in NBE over greater than three half lives when the catalyst concentration is less than 10 mM (correlation coefficients > 0.995). At higher catalyst concentrations we suspect that bimolecular decomposition reactions that destroy the alkylidene ligand compete with polymerization. We have found that kp = 0.027 (3) M ls l at 23 °C. Since kp/ki = 5 (0.5), ki = 0.0050 M ls l. PolyNBE can be cleaved from the metal by adding a large excess of benzaldehyde (e.g., 50 equiv). GPC analysis showed the samples to be essentially monodisperse, indicative of a well-behaved living polymerization. By proton NMR we can say that the double bonds in the polymer are -- 60% cis,... 

As can be seen in the two examples (cyclopentene and norbomene) polymerization of cyclic olefins leads to polymers containing double bonds at periodic intervals in their backbone. An interesting application of the metathesis polymerization is the preparation of tra 5-polyacetylene [1]. Metathesis of the tricylic monomer leads to the ring-opening of the cyclobutene ring to afford a polymeric derivative. Heating this polymer eliminates bis-trifluoromethylbenzene to leave behind traiis-polyacetylene (see Eq. 2.36). 

Subsequently, other Ti-cyclobutane species were shown to be the reaction products of the Tebbe complex with olefins the analogous reaction with acetylenes gives metallacyclobutenes." Utilization of Ti-metaUacycles as initiators in metathesis provides the first example of a living metathesis polymerization system. Clear evidence of the intervention of metaUacarbenes and metallacyclobutanes in olefin metathesis was later furnished by Kress et al. through minute nuclear magnetic resonance (NMR) studies on norbomene polymerization with tungsten alkylidenes. 

Norbomene polymerization is the most versatile of the cycloolefin addition polymerizations. Single-site catalysts such as metallocene compounds, constrained geometry catalysts (CGCs), and nickel or palladium diimine complexes, used in combination with MAO or borate cocatalysts, are active for the copolymerization of norbomene with ethene. The stmctme of the norbomene homo- and copolymers can be widely influenced by the symmetry and stmcture of the ligands on the transition metal complexes. 

Fig. 9 Plots of yield and values versus Al/Ti ratio in norbomene polymerization with 2-MMAO [34]...

Figure 9 Multicomponent catalysts for norbomene polymerization based on cationic palladium-phosphine complexes (X=CI, NO2, O2CCF3 R=Ph, n-Bu, f-Bu, CeFs).

Norbomene polymerization is the most versatile among the cycloolefm addition polymerizations. The structure of the norbomene homo- and copolymers can be widely influenced by the symmetry and structure of the ligands on the transition metal complexes. 

The P-H-elimination is impeded in the norbomene polymerization by the reformation of a highly strained ring system. The catalysts required for this reaction have a non-coordinating anion and weak nitril ligands as a characteristic. Such a pallatUum complex was described 1981 by Senn (5). The modification of this catalyst by Risse et al. resulted in a homogeneous reaction in the polymerization of norbomene (4). Vinyl polymerized norbomene is an example of conformationally restricted polymers having typically very high transition temperatures. 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

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). 

The idea of using polyunsaturated monomers is rooted in the eady history of acryUc elastomers. The first monomers used were butadiene [106-99-0] (35), isoprene [78-79-5] (36), and aHyl maleate [999-21-3] (37), but they did not find commercial success because during polymerization large portions of polymer were cross-linked. Other monomers have been proposed more recentiy tetrahydrobenzyl acrylate (38), dicyclopentenyl acrylate [2542-30-2] (39), and 5-ethyhdene-2-norbomene [16219-75-3] (40). The market potential, at least for the more recent ones, is stiU to be determined. 

The precise control of ROMP methodology has been exploited by Schrock and co-workers in the polymerization of a norbomene monomer functionalized with a distyrylbenzene side-chain 70 [1051. When calcium is used as a cathode, an internal device efficiency of 0.3% is observed and the peak emission is in the blue (475 nm). 

New kinds of living polymer systems result from the reactions of transition metals with cyclic, strained olefins 16). These polymerizations proceed through the intermediacy of metal carbenes and are exemplified by the polymerization of norbomene initiated by bis(cyclopentadienyl)-titane-cyclobutane described recently by Grubbs17>. 

Ethene/propene/diene monomer rubbers (EPDM) are elastomeric terpoly-mers used in the production of sealants, tubing and gaskets and, in the USA, is used in roofing applications. As the name suggests they are prepared by the polymerization of mixtures of ethene, propene and diene monomers, to form cross-links. By far the most common diene used is 5-ethylidene-2-norbomene (ENB). 

Figure 38 (a) The ADMET polymerization (using Mo and Ru catalysts) of symmetrical a.oj-dienes that yield main-chain boronate polymers (59). (b) The ROMP of several norbomene monomers containing methyl- and phenyl-substituted boronates into unsaturated polymers (60). (Adapted from ref. 84.)... 

Copper(II) triflate has also been used for the carbenoid cyclopropanation reaction of simple olefins like cyclohexene, 2-methylpropene, cis- or rran.y-2-butene and norbomene with vinyldiazomethane 2 26,27). Although the yields were low (20-38 %), this catalyst is far superior to other copper salts and chelates except for copper(II) hexafluoroacetylaeetonate [Cu(hfacac)2], which exhibits similar efficiency. However, highly nucleophilic vinyl ethers, such as dihydropyran and dihydrofuran cannot be cyclopropanated as they rapidly polymerize on contact with Cu(OTf)2. With these substrates, copper(II) trifluoroacetate or copper(II) hexafluoroacetylaeetonate have to be used. The vinylcyclopropanation is stereospecific with cis- and rra s-2-butene. The 7-vinylbicyclo[4.1.0]heptanes formed from cyclohexene are obtained with the same exo/endo ratio in both the Cu(OTf)2 and Cu(hfacac)2 catalyzed reaction. The... 

The resulting complexes can be effectively employed as single component catalysts to homopolymerize ethylene or copolymerize ethylene with acrylates [50, 51] and a variety of other polar monomers including vinyl ethers, [51,52] vinyl fluoride [53], iV-vinyl-2-pyrrolidinone, and AMsopropylacrylamide [54], In fact, the resulting catalysts are so robust that they can be used as single component catalysts in aqueous emulsion homo-polymerization of ethylene and copolymerization of ethylene with norbomenes and acylates [55]. 

ROMP reactions have been extensively carried out in water, and the first examples in liquid and scC02 [15] and ionic liquids [16] have been demonstrated. ROMP of norbomene and cyclooctene in scC02 exhibit a similar efficiency to that of chlorinated organic solvents. However, the carbon dioxide based system allows simple and highly convenient work-up of the polymer products. In [bdmim][PF6] (bdmim = 1-butyl-2,3-dimethylimidazolium cation), norbornene has been polymerized using a cationic catalyst as shown in Scheme 10.15. 

The optimum catalyst for a given reaction depends primarily on (a) the energetics of the reaction and (b) the functional groups present in the substrate. If, for instance, a strained cycloalkene such as norbomene or cyclobutene is to be polymerized, a catalyst of low activity will be sufficient to attain acceptable reaction rates. RCM... 

Week et al. [65] further reported the Co salen complex supported on norbomene polymers (23, 24) with stable phenylene-acetylene linker (Figure 8). The polymer-supported salen catalysts were investigated for HKR of the racemic terminal epoxides that showed outstanding catalytic activities and comparable selectivities to the original catalysts reported by Jacobsen. However, the polymeric catalyst was recycled only once after its precipitation with diethylether as the catalyst became less soluble and less reactive in subsequent catalytic... 

Norbomene end-capped polyimide oligomers (trade name LARC) are obtained by including 5-norbomene-2,3-dicarboxylic anhydride (nadic anhydride) (XLVII) in the polymerization reaction between a dianhydride and diamine [de Abajo, 1988 Hergenrother, 1987]. Heating the oligomer at 270-320°C results in a thermoset product. The main reaction... 

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