Abstract
Stereospecific polymerization of propylene was carried out with rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2) (1), rac-dimethylsilylenebis(indenyl)zirconium dichloride (rac-Me2Si(Ind)2ZrCl2) (2) and isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (i-Pr(Cp)(Flu)ZrCl2) (3) combined with trialkyl-aluminum (AIR3: R = C2H5, i-C4H9)/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) (4). In isospecific polymerization with 1 and 2, the molecular weight of polypropylenes decreased with increase in the molar ratio of AlEt3 (Et = C2H5)/Zr, whereas, an effect of AliBu3 (iBu = i-C4H9) concentration on molecular weight was not observed. The microstructures of resulting polypropylenes were studied by 13C n.m.r. and an increase in the molar ratio of ethyl end groups (derived from chain transfer to AlEt3) to n-propyl end groups (derived from β-hydrogen transfer) was observed with increase in the molar ratio of AlEt3Zr (1 and 2). The chain transfer reactions by both AlEt3 and AliBu3 were also detected in syndiospecific polymerization with 3. The molar ratio of alkyl (R) end groups (derived from chain transfer to AIR3) to n-propyl end groups was higher in the polypropylene obtained with AlEt3 than that obtained with AliBu3. The relative constants ktrAkp (ktrA = rate constant of chain transfer to AIR3, kp = rate constant of propagation) were determined by kinetic study.
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