Propylene polymerization catalyzed by constrained geometry (cyclopentadienyl)phenoxytitanium catalysts

Propylene polymerization was performed using three constrained geometry catalysts: 2-(tetramethylcyclopentadienyl)-4,6-di-tert-butylphenoxytitanium dichloride (1), 2-(tetramethylcyclopentadienyl)-6-tert-butylphenoxytitanium dichloride (2), and 2-(tetramethylcyclopentadienyl)-6-phenylphenoxytitanium dichloride (3) with Al(iBu)3/[Ph3C]+[B(PhF5)]4− as co-catalyst. The substituent effect of the ligand and the effect of the Al/Ti molar ratio on the catalytic properties were investigated. The catalytic activity decreases in the order of 1 > 2 > 3. The 13C NMR results show that the polymers are basically atactic polypropylene with some 2,1-insertion and 1,3-enchainment units in the polymer chain, and the end groups are mainly vinylidene (CH2CMe–) and vinyl (CH2CH–) together with a small amount of propenyl (CH3CHCH–). A possible chain propagation and termination mechanism of the propylene polymerization was discussed.

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