Polymers of norbomene

Conventional Ziegler-Natta catalysts, compounds, such as T1CI4 in combination with organoaluminum co-catalysts, have been used to prepare the addition polymer of norbomene (38). 

In assessing data on the proportions of cc, ct and tt pairs it is first necessary to ensure that the cis content has not been modified by the occurrence of secondary metathesis reactions. These can occur extremely rapidly with some polymer/catalyst systems. For example a polymer of cycloocta-1,4-diene initially contains no tt junctions, alternate double bonds in the polymer chain being derived from preformed cis double bonds in the monomer but under certain catalyst conditions tt junctions appear within a matter of seconds by secondary metathesis (14,15). These problems do not appear to be serious in polymers of norbomene derivatives presumably because the double bonds in the polymer are protected from secondary metathesis by the adjacent C5 rings and cannot compete when highly reactive monomer is still present. 

In polymers of norbomene it is observed (2) that the cis/trans distribution is blocky at high cis content but statistical at low... 

In the polymerization of using the same catalyst system the values of o., r and r, for the polymer prepared at Cm3 2-3M are 0.55, 1.3 and 0.9 respectively. These values are quite similar to those for the polymer of norbomene made under the same conditions. Furthermore, copolymerization studies. Table IV, show that norbor-nene and have similar reactivities. We shall see later that polymers of made under these conditions are atactic with respect to both cis and trans double bonds. It may therefore be assumed that polymers of norbomene made with this catalyst at monomer concentrations of 2-3M are also likely to be atactic. Hence the relaxation process observed at 0.6-0.1M (Figure 1) must involve either an epimerized form of P going to an achiral form or one achiral form going to another of different ligand geometry. 

NMR spectra of the ring-opened polymers of norbomene and its derivatives give information about their cis content, cis/trans distribution, HT or XN bias, and tacticity with respect to both cis and trans double bonds. The results indicate chat the propagating metal carbene complex sometimes contains a chiral reaction site and in other cases may be epimerized or achiral with respect to the reaction site. Relaxation processes other than epimerization must also sometimes be occurring, for example a change of geometry with respect to the metal centre. 

CHART 12.5 Structures of monomers and polymers employed in photolithography in 193 nm optical lithography. Most polymers are co-, ter-, and AVra-polymers of norbomenes bearing various substituents, /er Abutoxy ac ry I ales, adamantane, and maleimide. 

In the C NMR spectra of polymers of norbomene, all the ring carbons are sensitive to the configuration of the two nearest double bonds, while the olefinic carbons are sensitive to the three nearest double bonds, even though the third is five bonds away. The line positions are listed in Table 11.5. All these splittings disappear in the spectrum of the hydrogenated polymers so that none appear to be the result of m/r isomerism (Ivin 1977b Hamilton 1984a). 

The distribution of the cis and trans double bonds in a given polymer chain may be expressed in terms of the ratios r( = (tt)/(tc) and r. = (cc)/ ct). If the probability of formation of a cis double bond is independent of the configuration of the previous double bond, the distribution will be random (Bemoullian) and characterized by a single parameter r,= l/r. Figure 11.7 shows that this is the case for polymers of norbomene with less than 35% cis content, but for polymers with more than 50% cis content the distribution is generally somewhat blocky, with r,rc reaching values of 8 or more in some cases. 

Table 11.7 Polymers of norbomene derivatives showing m r splitting of the trans HH olefmic resonance in the C NMR spectrum X = eATO-5-substituent, Y = e/i o-5-substituent. Catalyst RUCI3.3H2O in EtOH/PhCl at 50-70°C, except where indicated otherwise (Ivin...

If norbomene is added to a mixture of WCl6/Me4Sn/cyclohexene (1/2.4/5) in toluene at 25°C, 5% of the cyclohexene is consumed and incorporated into the polymer of norbomene, as shown by the presence of 7.5% 1,6-hexanediol in the products obtained by ozonolysis of this polymer followed by reduction with LiAlH4. If the copolymer is allowed to stand overnight in the presence of the catalyst at 25°C the cyclohexene units are split out, with 99% recovery of the original cyclohexene. 

Table 13.1 Fraction of double bonds Cc having cis configuration in some polymers of norbomene formed by ROMP ...

We have seen that end-groups may be detected by C NMR spectra and inferred from mass spectra. Other methods for the detection of end-groups in the products of cross-metathesis of cyclic and acyclic olefins include IR and UV spectra, and elementary analysis. For example, polymers of norbomene made in the presence of pent-l-ene show a band at 1375 cm attributable to methyl groups, and bands at 905 and 990 cm due to vinyl groups (Porri 1974). Such bands become stronger relative to the main band as [M2]/[Mi] is increased, thereby reducing the MW. Polymers of cyclopentene made in the presence of 5-(j3-naphthoxypent-l-ene) have... 

Another difiinctional monomer, endo-cis-endo-hexacydo-[10.2.l.l .l .0 .0 ]heptadeca-6,13-diene was also used for the synthesis of star polymers. Using the arm-first approach, star polymers of norbomene, 5,6-bis (methox3methyl)norbomene (DMNBE) and 5,6-bis(dicarbotri-methylsilyloxy) norbomene (TMSNBE) were obtained. Amphiphilic star-block copolymers were prepared by reacting... 

TaUe 1 Jt Fraction of cis double bonds in ring-opened polymers of norbomene, norbor-nadiene and derivatives obtained with (Merent catalysts... 

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