Monocyclic cyclopentene derivatives

Compounds 19 (Makovetsky 1992a), 22 (Gunther 1970) and 23 (Feast 1980) do not polymerize, probably because their free energy of polymerization is positive. However, the fact that 1% of 19 can completely inhibit the polymerization of 20 and 21 indicates that it is likely to add preferentially to the active site forming the head carbene complex, [W](=CMeCH2CH2CH2CH=CHR), which is then unable to add any of these three monomers. It should be capable of copolymerization with norbomene. 3- and 4-Alkenylcyclopentenes have been tested as chain transfer agents for the ROMP of norbomene, but without much success (Schrock 1989). 

The ring-opened polymer of norbomadiene consists of 3,5-disubstituted cyclopentene units (24). When the concentration of these imits is kept below 0.2 M the polymer remains soluble, but above this concentration, in the presence of WCVMe4Sn (1/2), it gels. This is caused by cross-linking, brought about by the ROMP of the enchained cyclopentene rings (see Section 13.4.1.1). 

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Polymers formed by ROMP of unsubstituted monocyclic olefins such as cyclopentene [29] contain double bonds that may be cis or trans (1). NMR spectra give not only the proportions of cis and trans double bonds but also the proportions of cc, cr, and tt dyads. Low-cw polymers of norbornene and derivatives usually have a random distribution of the two kinds of double bond but in high-cw polymers the trans double bonds frequently occur in pairs, indicating an influence of the double bond one removed... 

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