The catalytic activities of non‐metallocene type chromium, half‐sandwich type chromium and metallocene type chromium complexes for the polymerization of ethylene were explored using MAO, modified MAO (MMAO) or BuAO in the presence or absence of a silica support. The complexes, Cr[N(SiMe3)2]3 (1), Cr[CH(SiMe3)2]3 (2), Cr(CH2SiMe3)4 (3), and Cr(CH2CMe3)4 (4), displayed good catalytic activities for the polymerization of ethylene in the presence of excess MAO or MMAO. The activities exceed 103 g‐PE/Cr‐mol·h to lead to polymers with Mw > 80×104. The molecular weight distributions are rather narrow in cases of complexes 1 and 2. More efficient catalysis was observed when C5Me4‐CH2CH2NMe2CrCl2 (5) and C5H4CH2CH2N(iPr)2CrCl2 (6) were used coupling with MMAO in the presence of a silica support. The Mw increased to 276.2×104 and the Mw/Mw value decreased into 2.2 in the case of complex 5. The catalysis of (C5H5)2Cr (7) in the presence of a silica support is very high and the complex (7) produced high molecular weight polyethylene with narrow molecular weight distribution, while [1,3‐(SiMe3)2C5H3]2Cr (8) shows only a little catalytic activities presumably due to its very weak interaction with a silica support.

1-(2-N,N-Dimethylaminoethyl)-2,3,4,5-tetramethylcyclopentadienyl-chromium dichloride (1), (2-N,N-dimethylaminoethyl)cyclopentadienylchromium dichloride (6), and (2-N,N-dimethylaminoethyl)indenylchromium dichloride (7) in the presence of modified methylaluminoxane exhibit high catalytic activities for the polymerization of ethylene with random copolymerizations of ethylene with propylene, ethylene with 1-hexene, and propylene with 1-hexene. These initiators conduct polymerizations to give high molecular weight polymers with low polydispersities. However, the stereoregularities are very poor in these reactions.

Abstract:New approaches to organo-transition-metal catalyzed-polymerizations of methyl methacrylate

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