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(SiMe 3 ) 2 ] 3 (1), Cr[CH(Si-Me 3 ) 2 ] 3 (2), Cr(CH 2 SiMe 3 ) 4 (3), and Cr(CH 2 CMe 3 ) 4 (4), displayed good catalytic activities for the polymerization of ethylene in the presence of excess MAO or MMAO. The activities exceed 10 3 g-PE/Cr-mol.h to Iead to poly mers with M w > 80 × 10 4 . The molecular weight distributions are rather narrow in cases of complexes 1 and 2. More efficient catalysis was observed when C 5 Me 4 -CH 2 CH 2 NMe 2 CrCl 2 (5) and C 5 H 4 CH 2 CH 2 N(iPr) 2 CrCl 2 (6) were used coupling with MMAO in the presence of a silica support. The M w increased to 276.2 × 10 4 and the M w /M n value decreased into 2.2 in the case of complex 5. The catalysis of (C 5 H 5 ) 2 Cr (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-(SiMe 3 ) 2 C 5 H 3 ] 2 Cr (8) shows only a little catalytic activities presumably due to its very weak interaction with a silica support.