THE MICROSTRUCTURE OF POLY(CYCLOPENTENE) PRODUCED BY POLYMERIZATION OF CYCLOPENTENE WITH HOMOGENEOUS ZIEGLER-NATTA CATALYSTS

The hydro-oligomerization of cyclopentene in toluene solution using [ethylenebis(eta-5-indenyl)]-zirconium dichloride (1) or bis(cyclopentadienyl)zirconium dichloride and methylaluminoxane as catalysts was studied. The crude oligomer mixture obtained using the former catalyst was extracted with hot toluene to provide a fraction consisting predominantly of dimer, trimer, and tetramer. Distillation provided trimer of 99% purity. Pure tetramer was precipitated from methanol-toluene as a crystalline solid. Hydro-oligomerization of cyclopentene with zirconocene dichloride as catalyst provided two tetramers, one of which was identical to that produced using the chiral catalyst. The structure of the trimer, including stereochemistry, was established by total synthesis. These results conclusively demonstrate that the original structure assigned to poly(cyclopentene) is incorrect and that enchainment of cyclopentene occurs predominantly by cis-1,3-insertion. A mechanism for the polymerization of cyclopentene using catalyst 1 is discussed.