Norbornene oligomerization

Scheme 4.2 Norbornene oligomerization using bis(pentafluorophenyl)nickel.

Polymerization of norbornene using chiral metallocenes results in insoluble polymers exhibiting a glass transition temperature of about 210 °C. Although they have been shown by oligomerization to be tactic, no melting up to 500 °C... 

Fig. 4.20 Catalytic cycle for oligomerization of norbornene using ethylene as a chain transfer agent.

The experiment using BF3 Et2O did give a low molecular weight oil upon evaporation of the solvent and residual monomer, which was indicative of a cationic oligomerization of norbornene. 

In 1993, Perez et al. reported norbornene polymerization in aqueous emulsion at 70 °C using PdCl2 as a catalyst precursor [92, 93]. A stable latex consisting of low-molecular-weight oligomeric material (degree of polymerization DP ca. 10) was obtained with low catalyst activities (70 TO h ). Very small latex particles of 10 to 20 nm diameter were reported. In the free radical polymerization of olefinic monomers such small particles are only obtained by microemulsion polymeriza-... 

A direct way of preparing a palladacycle was found for the special case of m-bromocyanobenzene which was reacted with Pd(PPh3)4 and norbornene in anisole at 105 °C. The palladacycle precipitated in an oligomeric form from the reaction solution in good yields (67% on Pd). The complex contains one molecule of triphenylphosphine per palladium and a coordination site is occupied by the cyano group of another palladacycle unit. (Eq. 11) [21]. 

Maleic anhydride was used as the dienophile, allowing for further functionalization following the assembly of the norbornene skeleton. Diels-Alder cycloadditions of the above-mentioned fiilvene derivatives with maleic anhydride at elevated temperatures, between 80 °C and 120 °C, and moderate concentrations, 0.2 to 0.5 M, afforded quantitative yields of the corresponding norbornene derivatives 5, 7, and anhydride precursor of 9 (see Table I) (29). At total adduct concentrations above 1.5 M or temperatures above 130 °C, a solid oligomeric side product, presumably a copolymer of the reactants, was obtained. Two isomers, endo or exo, can be obtained from cycloaddition reactions, depending on the nature of adducts or the reaction temperature. These isomers exhibit different polymerization kinetics, where, in most cases, endo adducts polymerize very slowly, and result in low conversions. 

An exception to difficult-to-model filled systems is provided by the norbomene-POSS pol5miers studied by Bharadwaj and co-workers (278). POSS is polyhedral oligomeric silseqiuoxane—groups that are pendant from the poly(norbornene) chains of the model. This can be viewed as a filled system, but one in which the filler is nanoscopic and chemically bonded to the chains. The simulations were done to determine Tg, density, thermal expansion, solubility parameter, POSS mobilities, and elastic moduli in a wide-ranging study. They conclude that the ponderous nature of the POSS moieties is largely responsible for the reinforcing effect. 

Laverty, D. T. Rooney, J. J. Mechanism of initiation of the ring-opening polymerization and addition oligomerization of norbornene using unicomponent metathesis catalysts. J. Chem. Soc., Faraday Trans. 1 1983, 79, 869-878. 

Recently, ROMP of silicon-containing norbornenes was used for creation of inorganic-organic hybrid materials. Particularly, incorporation of the polyhedral oligomeric silsesquioxanes molecule (POSS) in norbornene and its ROMP copolymerization with norbornene or norbornene-dicarboxylic acid gave POSS-containing copolymers [208, 209],... 

Concentrated sulphuric acid has been initially used for dimerization and oligomerization of cyclic monoolefins such as cyclohexene and diolefins such as cyclo-pentadiene, and later on for indene-coumarone fractions. Diluted sulphuric acid and benezenesulpho-nic acid have been further employed for the polymerization of more active cycloolefins like norbornene and dicyclopentadiene. In these reactions, monomer conversion, product yield and molecular mass depended largely on the acid concentration and monomer nature as well as on the other reaction parameters. Various compositions of initiators containing sulphuric acid in association with phosphoric acid, boric acid, sulphonic acids or inorganic sulphates of the type M (S04) (M = Al, Cr, Mg, Co, V) have also been reported for the polymerization of unsaturated alicyclic and cyclic fractions and for reactions with heavy aromatic fractions in hydrocarbon resin synthesis [2]. 

Multiblock polymeric networks are the logical extension of the homopolymer as it is essentially two or more homopolymers covalently attached in a linear fashion. For many applications, the result is rather simplistic in frmctionality. An early example of block copolymers used a titanacyclobutane to effectuate the polymerization of norbornene, norbomadiene derivatives, and cyclopentadiene into diblock or triblock hydrocarbon copolymers with PDIs of 1.08-1.14. The ROMP of cyclobutadiene using a tungsten catalyst followed by hydrogenation yielded polyethylene or instead of hydrogenation, it can be used to form diblocks and triblocks with norbomadiene." The ability to form block copolymers can be a test of the efficiency of a catalyst as was done with the third-generation Cmbbs catalyst by Stelzer in which oligomeric norbornyl monomers were used to synthesize homopolymers, diblocks. 

Following the pioneering work on the synthesis of [x.3.0] bicychc systems by RRM from norbornene derivatives [35], Aube et al. applied this strategy to synthesize indolizidine alkaloid 251F, where enone 76 was obtained from the rearrangement of norbornene 75 (Scheme 11.20) (36). Early attempts afforded the desired product in only poor yield (30%) mainly because of olefin oligomerization. Under an atmosphere of ethylene, it was possible to optimize the metathesis cascade and the bicyclic compound 76 was isolated in 93% yield with the use of catalyst [Ru]-I (5 mol%). 

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