Racemic polymers alternating copolymers

All resonances in the C NMR spectra of all-HT polymers of racemic 1-methylnorbomene are insensitive to tactieity, but C-6 in the spectrum of the hydrogenated polymer does show mtr splitting (0.05 ppm), when the precursor is made with OSCI3 as catalyst. The downfield component (39.12 ppm) is dominant when the experiment is repeated with partially resolved monomer and is therefore assigned to m dyads. The upheld component (39.05 ppm) is the only peak observed in the spectrum of the hydrogenated all-cis, all-HT polymer made from racemic monomer with ReCls as catalyst, and it may be concluded that this is a syndiotactic alternating copolymer of the two enantiomers. This stracture is forced on the polymer by the steric exclusion of cis HH stmctures, which are never observed in any polymers of this monomer (Hamilton 1983, 1984a also see Couturier 1992). 

The same catalysts also made all-cis, fully head-to-tail biased, syndiotactic polymers from ( )-l-methylNBE. Such materials are alternating copolymers of enantiomers and in accord with expectation the resolved monomer refuses to polymerize with ReCls as catalyst [12]. In ROMP of these derivatives only the exo face of the olefmic bond is attacked, but there are two molecular forms in the racemic mixture. Subject to the... 

When measuring vinyl polymer tactlclty, one prefers the longest complete n-ad distribution available as well as the translated simplest comonomer distribution, possibly m versus r. An alternative exists to the m versus r distribution In the form of number average or mean sequence lengths. If any vinyl homopolymer Is viewed conceptually as a copolymer of meso and racemic dyads, mean sequence lengths can be determined for continuous runs of both meso and racemic configurations (32), that Is,... 

In the case of a chiral monomer, sequences of the resultant polymer should be directly influenced by the stereoselectivity of these interactive moieties." if the interactive moiety prefers homochiral association, two enantiomeric polymers of individual optical antipodes should be afforded. Contrary to this, when the interactive moiety possesses a strong tendency to adhere another monomer with opposite handedness, an alternative eopolymer of each enantiomer is expected to arise. On the other hand, the monomer with no stereoselectivity will give a random copolymer. Studies on the supramolecular polymerization of racemic monomers are of significant importance, because these three extreme cases are regarded as the simplest models of the molecular arrangements in crystalline states, conglomerates, racemic compounds, and racemic mixtures, respectively. 

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