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SynopsisThe stereoselectivity of the cyclooctene ring-opening polymerization in the presence of the tungsten hexachloride-tetraisobutylalumoxane (TBAO) catalyst system has been studied. The reaction conditions have been established in which the polymer chain isomerization is reduced to a minimum. Under these conditions the stereoselectivity is determined by an individual act of the monomer molecule insertion. The dependence of stereoselectivity on monomer concentration, number of active sites, and temperature has been investigated. The results obtained suggest that the cyclooctene polymerization is selective in favor of the geometrical configuration of the starting cyclmlefin (the "retention" effect) by analogy with the previously reported metathesis of acyclic olefm. Considerations which support the idea that cis and trans units are reproduced by the same type of active sites are discussed. The experimental evidence indicates that in this case the stereoselectivity is determined by the difference in kinetics of two reaction paths of the monomer molecule insertion that lead to the formation of cis and trans units. , (:z5-+ f C H 3 + ,cCi"i + , ( 2 s + XCH2 CH3 CH, C,H, C2Hs C J &The stereoselectivity with respect to butenes is given by formula (1):[cp]'"] and [Cyan'] are the concentrations of cis-and trans-2-butene, respectively. Here the "retention" effect is 1 2 limt-o S > 0.5, where t is time.Investigation of this effect presents difficulties because the difference in structure and reactivity of the starting olefin and metathesis products is too small to allow easy determination of the composition of the initial reaction products.6 It is anticipated that in cycloolefin polymerization which leads to the formation of only two products, that is, cis and trans units (instead of the five products formed in the 2-pentene metathesis), the "retention" effect will be more easily detectable.

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