| Research Abstract |
The purpose on this research project is to create new polyolefins that possess unique properties. Olefin polymerization by homogeneous transition metal complex catalysts attracts particular attention in the field of organometallic chemistry, catalysis, and polymer chemistry. This is because the design of an efficient complex catalyst has thus been the key for the precise synthesis by controlled polymerization. We have shown that (cyclopentadienyl)(aryloxy)titanium (IV) complex of the type, Cp'Ti(OAr)X_2 (OAr=aryloxy group), exhibited remarkable catalytic activities for ethylene, α-olefin polymerization in the presence of methylaluminoxane (MAO), and monomer reactivities as well as monomer sequence distributions were directly affected by the substituents in cyclopentadienyl group. We have also shown that the catalyst of this type could be tuned to the efficient catalyst precursor for both styrene polymerization and ethylene/styrene copolymerization by the simple ligand modification. We
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have also shown that efiicient norbornene incorporation in ethylene/norbornene copolymerization can be achieved in this catalyst systems by modifying the substitutent on cyclopentadienyl group like (indenyl)TiCl_2(OAr). Based on these facts, new polyolefins that were difficult/impossible to prepare have been created by using this catalysts. We also explored the effect of ligand in olefin polymerization chemistry by Cp-anilide, Cp-amide and Cp-ketimide titanium complexes. (Anilido)(cyclopentadienyl)titanium(IV)complexes of the type, Cp'TrCl_2[N(R)(XAr)] [Cp'=Cp^*, 1,3 M_2C_5H_3,Cp ; R=SiMe_3 etc.; Ar=2,6-Me_2C_6H_3], and Cp'-amide titanium complexes of the type, Cp'TiCl_2(NMeR) have been prepared, and these complexes exhibited high catalytic activity for ethylene polymerization in the presence of MAO, and the activity increased in the order : Cp'=Cp^*>1,3-Me_2C_5H_3>Cp. The trend observed here was almost the same as that in Cp'-aryloxy titanium complexes. The efficient catalyst for symdiospecific styrene polymerization could be modified only by replacing the substituent on Cp'.
We have reported that (arylimido)(aryloxo)vanadium(V) complexes of the type, VCl_2(NAr)(OAr'), exhibited remarkable catalytic activities for ethylene polymerization in the presence of MAO, and that ring-opening metathesis polymerization (ROMP) of norbornene had been initiated by V(CH_2Ph)_2(NAr)(O-2,6Pr_2C_6H_3). Remarkably high catalytic activities for ethylene polymerization were observed if the complex was treated with Et_2AlCl. The low catalytic activity was observed if AlMe_3 was used in place of Et_2AlCl, although the use of AlMe_3 as cocatalyst was effective for the ROMP. We believe that the results observed here would be an interesting contrast among these polymerizations. Less
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