Zirconocenes as Initiators for Carbocationic Isobutene Homo- and Copolymerizations

Abstract

The zirconocene complexes Cp2ZrMe2 and Cp*2ZrMe2 activated with B(C6F5)3 initiate the carbocationic polymerization of isobutene and isobutene-isoprene copolymerizations to IIR rubbers at temperatures as high as -30°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 presence 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 effectiveness of zirconocene dialkyls with that of the metallocene hydrolysis products Cp* 2Zr(OH)2 and (Cp2ZrMe)2(µ-O) in the presence of B(C6F5)3 suggests that initiation by traces of protons is less efficient than initiation by cationic metallocene alkyl species, while oxo-bridged complexes (Cp′2ZrMe)2(µ-O)/B(C6F5)3 (Cp′ ) C5H5 or C5H4SiMe3) are inactive.

Methacrylate Polymerization using a Dinuclear Zirconocene Initiator: A New Approach for the Controlled Synthesis of Methacrylate Polymers

“…We concentrated on the use of dinuclear zirconocene complexes featuring the μ‐oxo linkage as this unit is robust 5. 6 The dinuclear ion‐pair [(Cp 2 Zr) 2 (μ‐Me)(μ‐O)][MeB(C 6 F 5 ) 3 ]7 formed in situ from [{Cp 2 Zr(Me)} 2 O]6 and B(C 6 F 5 ) 3 was inactive in MMA polymerization, and as enolate complexes often prove to be effective initiators when the corresponding alkyls do not (e.g. ref.…”

Reactivity of Metallocene Catalysts for Olefin Polymerization: Influence of Activator Nature and Structure

“…Even though B(C 6 F 5 ) 3 alone is capable of polymerizing isobutylene, the rate of polymerization is very slow. [188] Since these polymerizations can be conducted in nonhalogenated solvents like toluene (different from classical cationic polymerizations in which halogenated solvents are a must) they attracted much industrial interest as well as earned the name environmentally clean or green technology.…”

Arylzinc Complexes as New Initiator Systems for the Production of Isobutene Copolymers with High Isoprene Content

“…Other examples include BCl 3 , [1,5] chelating boranes, [6] and a variety of transition-metal halides, for example, TiCl 4 , VCl 4 , and FeBr 3 . [7][8][9] Organometallic Lewis acids paired with extremely weakly coordinating anions, such as [AlCp 2 Me]/B(C 6 F 5 ) 3 , [10] [SiMe 3 ][B(C 6 F 5 ) 4 ], [11] [Cp*TiMe 3 ]/B(C 6 F 5 ) 3 (Cp* = C 5 Me 5 ), [12] and [(Cp R ) 2 [13][14][15] have also been found effective. However, to our knowledge there are no reports to date on the use of zinc compounds in IB homo-and co-polymerizations.…”