Additive effects of alkylaluminium compounds on propylene-1,3-butadiene copolymerization using isospecific zirconocene catalysts

Additive effects of diisobutylaluminum hydride (DiBAL-H) was studied in copolymerization of propylene and 1,3-butadiene with a series of C2-symmetric ansa-bis(indenyl)zirconocene derivatives, i.e., rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride (4Ph), dichloride, rac-dimethylsilylbis(2-methyl-benzoindenyl)zirconium dichloride (Bz), rac-dimethylsilylbis(2-methyl-indenyl) zirconium dichloride (2Me), rac-dimethylsilylbis(1-indenyl)zirconium dichloride (1-Ind), rac-ethylenebis(1-indenyl)zirconium dichloride (Et-Ind), activated by modified methylaluminoxane (MMAO). Without DiBAL-H, the activity of the copolymerization decreased in the following order, 2Me > 1-Ind > Et-Ind > 4Ph ≈ Bz, whereas butadiene content decreased in the following order, 4Ph > Bz ≥ Et-Ind ≥ 1-Ind > 2Me ≈ 0.1 mol%. The addition of DiBAL-H affected the activity but hardly changed the butadiene content. The copolymer obtained without DiBAL-H contained the butadiene units of 1,2-insertion (1,2-BD) and 1,4-insertion (1,4-BD). The addition of DiBAL-H decreased the amount of 1,4-BD and produced hydrogenated 1,4-BD in the 4Ph and Bz systems accompanied by the increase of the copolymerization activity. The additive effect of other alkylaluminums was investigated in the Bz system, and DEAL-H was found to show the similar effects with DiBAL-H. The 13C NMR analysis of the polymer terminated with deutrated methanol indicated the hydroalumination of 1,4-BD in the Bz system. Hydroxyl groups can be also introduced by oxidative cleavages of the Al–C bonds.