Contents 8 Ring-opening Reactions

Other monocyclic monomers will imdergo ring-opening reactions cyclobutene and 1-methyl cyclobutene produce polybutadiene and cis-polyisoprene, respectively but this synthetic route cannot compete with estabhshed methods for preparing synthetic elastomers. Reactions are slower with the larger rings, as the strain decreases, but a useful elastomer with a high trans content and well-developed crystallinity (such as the product sold under the trade name Vestenamer) can be prepared from cis-cyclooctene (the trans compound is umeactive). 

We have reported the first example of a ring-opening metathesis polymerization in C02 [144,145]. In this work, bicyclo[2.2.1]hept-2-ene (norbornene) was polymerized in C02 and C02/methanol mixtures using a Ru(H20)6(tos)2 initiator (see Scheme 6). These reactions were carried out at 65 °C and pressure was varied from 60 to 345 bar they resulted in poly(norbornene) with similar conversions and molecular weights as those obtained in other solvent systems. JH NMR spectroscopy of the poly(norbornene) showed that the product from a polymerization in pure methanol had the same structure as the product from the polymerization in pure C02. More interestingly, it was shown that the cis/trans ratio of the polymer microstructure can be controlled by the addition of a methanol cosolvent to the polymerization medium (see Fig. 12). The poly(norbornene) prepared in pure methanol or in methanol/C02 mixtures had a very high trans-vinylene content, while the polymer prepared in pure C02 had very high ds-vinylene content. These results can be explained by the solvent effects on relative populations of the two different possible metal... 

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