STEREOSELECTIVITY OF CYCLOOLEFIN POLYMERIZATION WITH WCL6-BASED CATALYTIC-SYSTEMS

The stereochemistry of ring-opening metathesis polymerization of sever al cycloolefins (cyclopentene, cyclooctene, 1,5-cyclooctadiene, cyclod odecene) in the presence of WCl6-based catalysts (WCl6/iBu3Al/epichlor ohydrin, WCl6/iBu3Al/Chloranil, WCl6/phenylacetylene, WCl6/Ph4Sn, WCl6 /allyl4Si, WCl6/iBu2AlOAliBu2) has been carefully examined. The produc t stereoselectivity and polymer microstructure were greatly dependent on the nature of the catalytic system and reaction conditions; the nat ure of the cycloolefin also influenced the steric course of the reacti on. An important stereochemical consequence was that the cis and trans content of the polyalkenamer greatly depended on the oxidation state of the W-atom, catalyst activity and reaction temperature. The relatio nship between the microstructure of several polyalkenamers (polypenten amer, polyoctenamer, polydodecenamer) obtained with the above catalyti c systems and cycloolefin reactivity or catalyst nature is fully illus trated. The role of the ligand as well as of the cocatalyst and activa tor is also shown. The particular stereochemical behaviour of cycloole fins in the presence of the studied WCl6-based catalytic systems is di scussed in terms of the metallacarbene-metallacyclobutane mechanism. T he steric effects induced by the coordinating cycloolefin and the exis ting ligands at the transition metal are also considered.