Norbornene-derived monomers

The living character of the ROMP promoted by the initiator Ru(CHPh)(Cl)2 (PCy3)2 (Cy = cyclohexane) was tested with the synthesis of diblock, triblock, and tetrablock copolymers of norbornene derivatives carrying acetyl-protected glucose, [2,3,4,6-tetra-O-acetyl-glucos-l-O-yl 5-norbornene-2-carboxylate], A or maltose groups, [2,3,6,2/,3/,4/,6/-hepta-0-acetyl-maltos-1-O-yl 5-norbornene-2-carboxylate], B, shown in Scheme 41 [102]. The AB, ABA, and ABAB structures were prepared by sequential addition of monomers with narrow molecular weight distributions to quantitative conversions. 

Chen initiated the study of ruthenium-catalyzed reactions in solution in 2000 by doping a charged norbornene derivative into a solution containing catalyst and normal norbornene (Fig. 12). Initially the ruthenium catalyst is neutral and invisible by ESI-MS but as the norbornene monomers are incorporated, the mass spectrum shows a series of resting states of the catalyst after n additions of the monomer. 

Ungerank et al. investigated the influence of different molybdenum Schrock-type initiators 1, 2 and 3 (see Fig. 2) on the polymerization of ( )- and (-)-exo,e tdo-bis[4 -cyanobiphenyl-4-yl)oxyalkyl]norborn-5-ene-2,3-dicarboxy-lates [( )-IV-n and (-)-IV-n] [47]. The initiator had a strong influence on the Z/E ratio of the double bond in the polymer chain and therefore also on the tacticity of the polymer chain. Using racemic 2,3-disubstituted norbornene derivatives, such as ( )-IV-n, the two adjacent monomers (diads) can in principle form eight different stereoisomers, as depicted in Fig. 5 [48]. 

The introduction of perfluorinated groups generally favors microphase separation due to the immiscibility of fluorocarbons with hydrocarbons [66]. Norbornene derivatives with perfluorinated endgroups in the side chain were prepared by Wewerka et al. [67]. Monomer XII contained a relatively long (CF2)8-chain, separated via a long spacer (11 methylene-groups) from the norbornene, whereas monomer XIII has two relatively short (CH2)2(CF2)4-side chains (Fig. 11). Homopolymers and block copolymers were synthesized with one fluorinated monomer (XII or XIII) and one non-fluorinated non-liquid crystalline monomer (NBDE or COEN) with the Schrock-type initiators 4 and 5, respectively, leading to microphase-separated block copolymers. Table 9 and Table 10 summarize the physico-chemical properties of the homopolymers and block copolymers. 

Fig. 12 Monomers used for the copolymerization of norbornene derivatives with alkynes...

This has two detrimental effects on polymerization. First, chelation strengthens the metal-olefin interaction, thereby raising the barrier for the insertion step. Second, it forces insertion through the endo face, in sharp contrast to the known propensity for norbornene to insert into metal-carbon bonds through the less hindered exo face [3 a, 5]. Consistent with this hypothesis has been our observation of the preferential uptake of the exo isomer in the polymerization of functional norbornene derivatives by Pd(PRj)(Me). For example. Fig. 9.3 shows the uptake profile versus time for the polymerization of 5-norbornene-2-carboxyhc acid ethyl ester starting with a monomer isomer ratio of 22% exo to 78% endo. Indeed, under certain conditions a polymer can be obtained from the exo isomer but not the endo isomer [10]. 

Various monomers which fail to undergo polymerization under these conditions are designated "unreactive . However, effective polymerization of these monomers, e.g. maleic anhydride (MAH) and norbornene derivatives, is initiated in bulk or in concentrated solutions, at temperatures where a radical precursor has a short half life, i.e. less than 60 min. It is apparent that these polymerizations require more than the availability of free radicals and that other factors prevail under these conditions. 

The norbornene derivatives in Table II do not have a plane of symmetry and exist in optically active forms in which the double bonds carry a small dipole. The polymers made from racemic monomers of this kind may contain three types of dyad depending on the relative orientation of the substituents, as illustrated in 13P and 14P,... 

These complexes also functioned well in benzene, although small amounts of ethanol were necessary to initiate polymerization. The order of activity for these catalysts was Ir(III) > Os(III) > Ru(III), and they were found to polymerize monomers with exo substituents more readily than endo isomers. Rinehart and Smith later demonstrated that these complexes initiated the aqueous polymerization of a substituted norbornene derivative in the presence of anionic emulsifiers and suitable reducing agents [24]. This reaction gave particularly low yields of polymer (typically less than 9%), but the overall tolerance of these complexes to polar and protic functionalities made them ideal candidates for further study. 

Yang and Luh used ROM to prepare a further example of a norbornene-derived phosphine-substituted polymer. Starting from 1,4-benzoquinone, monomer 25 was prepared in three steps. This was then polymerized at room... 

Fused ring monomers other than norbornene derivatives... 

ROMP of norbornadiene derivatives. Preliminary results have shown that treatment of cyclopentadiene with butynedioic acid gave norbornadiene diacid 8, which could be coupled to glycine methyl ester to give monomer 9 (Scheme 3). Compound 9 was found to undergo ROMP when treated with initiator 3, and gave a polymer with a narrow molecular weight distribution. However, the synthesis of this class of monomer was more difficult than the synthesis of norbornene derivatives, so it was not pursued further. 

Diazanorborn-5-ene derivatives are known to equilibrate between endo-cis, exo-cis, and (in some cases) trans-isomQrs as shown in Scheme 4 and Scheme 5. Thus it was felt that these systems may be as readily prepared as the endo-isomQvs of norbornene derivatives, but undergo ROMP as easily as the jc< -isomers. To test this hypothesis, four such monomers were prepared 10-13, two of which are diester derivatives 10-11 (Scheme 4) and the other two of which are imides 12-13 (Scheme 5). The ester derivatives are in equilibrium with a trans-isomQv, whilst imides have only c/5-isomers, but have smaller substituents than the diesters. 

Introduction of proper pendant groups in monomer unit of addition polynor-bornene is the way to get polynorbornenes with desired properties. However, the appearance of substituents in norbornene molecules resulted in a decrease of their activity as monomers [220, 223]. In the case of ROMP, this effect is softened to some extent by substantial thermodynamic driving force in the process appearing as a result of opening highly strained bicyclic norbornene skeleton (see Table 1). AP is not such a thermodynamically favorable process. Therefore, in this case the introduction of side substituents, especially bulky or functional groups, led to a dramatic decrease in activity of norbornene derivatives [224-227]. Probably, this fact is one of the reasons for the limited number of publications devoted to AP of silyl substituted norbornenes. 

In contrast to bis-SiMey-norbornene derivatives, disubstituted tricyclononenes turned out to be active monomers in AP [238, 240]. In tricyclononene molecule both MesSi-groups are moved by an additional one C-C bond away from the double bond and therefore from the reaction catalytic center. Synthesis of bis-MesSi-substituted tricyclononene was carried out from quadricyclane and fran5-l,2-bis(trichlorosilyl)ethylene. This route of synthesis provided formation of norbomene-type monomers with 100% exo-configuration of cyclobutane fragment that reduced steric hindrances in AP. That is why this monomer was active in AP catalyzed with common Ni- and Pd-catalyst systems. As a result, the formation of highly molecular weight polymer (Af up to 500,000 was observed [196]. 

The present paper reports the ring-opening polymerization of norbornene derivatives substituted by nitrile, amide, imide, ester, pyridyl and acid anhydride groups by the above-mentioned catalysts. The polymerization behavior of these monomers and the physical properties of the polymers of norbornenenitriles will be described. 

A great number of norbornene-like monomers [e.g., m = 1-3, R] and R2 = alkyl and aryl groups, Eqs. (103) and (104)] with or without substituents have been employed in polymerization reactions induced by Ziegler-Natta and ROMP catalysts derived from ruthenium, osmium, iridium, palladium, platinum, molybdenum, and tungsten halides or vanadium and zirconium halides or acetylacetonate associated with organometallic compounds [162, 163]. Both addition and ring-opened polymers have been obtained by this way depending on the catalyst employed [Eqs. (103) and (104)]. 

The role of the electron-donating component is essential in determining both the monomer reactivity and the copolymer structure. The physical and mechanical properties of these products may be altered gradually by modifying the catalyst composition within desired limits. Other norbornene derivatives, such as compounds (30-32), find valuable... 

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