Ethylene polymerizations with alkyl-, disilylamino-and cyclopentadienylchromium/MMAO initiators

Abstract

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 M̄w > 80 × 104. The molecular weight distributions are rather narrow in cases of complexes 1 and 2. More efficient catalysis was observed when C5Me4CH2CH2NMe2CrCl 2 (5) and C5H4CH2CH2N(iPr) 2CrCl2 (6) were used coupling with MMAO in the presence of a sjlica support. The M̄w increased to 276.2 × 104 and the M̄w/M̄n 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. © Wiley-VCH Verlag GmbH, 2001.