ZIRCONOCENES AS INITIATORS FOR CARBOCATIONIC ISOBUTENE HOMOPOLYMERIZATION AND COPOLYMERIZATION

The zirconocene complexes Cp2ZrMe2 and Cp-2ZrMe2 activated with B(C6F 5)(3) initiate the carbocationic polymerization of isobutene and isobu tene-isoprene copolymerizations to IIR rubbers at temperatures as high as -30 degrees C. Unlike conventional metal halide initiators, these metallocene-based initiator systems produce both homo- and copolymers of broadly similar molecular weights. Copolymers prepared in the prese nce of ca. 2 mol % isoprene show a diene incorporation rate of 1.4-1.7 %, with the typical 1,4-trans structure. Comparison of the effectivene ss of zirconocene dialkyls with that of the metallocene hydrolysis pro ducts Cp-2Zr(OH)(2) and (Cp2ZrMe)(2)(mu-O) in the presence of B(C6F5) (3) suggests that initiation by traces of protons is less efficient th an initiation by cationic metallocene alkyl species, while oxo-bridged complexes (Cp-2'ZrMe)(2)(mu-O)/B(C6F5)(3) (Cp' = C5H5 or C5H4SiMe3) a re inactive.