| 초록 |
Effects of B(C6F5)3 on the activation of Ni(0) and Ni(II) complexes were investigated in the polymerization of norbornene. A catalyst of Ni(0) complex, bis(1,5-cyclooctadiene)nickel (Ni(COD)2, biacetylbis(2,6-diisopropylphenylimmine)(1,3-butadiene)nickel, or tetrakis(triphenylphosphine)nickel, with B(C6F5)3 was found to have high catalytic activity in the polymerization of norbornene. The catalysts were also found to provide polymer having a high molecular weight (Mn) of over 2 X 105 under suitable conditions even in the absence of AlR3 and MAO. On the other hand, the catalyst of Ni(II) complex/B(C6F5)3 did not provide any catalytic activity at all under analogous conditions, regardless of the structure of Ni(II) complex. Ni(II) complexes showed catalytic activity only when MAO was employed together with Ni(II) complex and B(C6F5)3. The use of other borane compounds such as B(C6H5)3, BEt3, and BF3 etherate with Ni(COD)2 in place of B(C6F5)3 showed clearly the main function of B(C6F5)3 in the present catalyst. The high Lewis acidity of B(C6F5)3 enabled it to activate catalytic complexes, thus inducing the polymerization. The study of 1H-, 13C- and 19F-NMR spectra of the polynorbornene produced with Ni(COD)2 and B(C6F5)3 definitely showed that initiation of polymerization occurred via insertion of the exo face of the norbornene into the Ni-C bond of the C6F5 ligand. |
