Jifu Bi

Highly Active and Cis-1, 4 Selective Polymerization of 1, 3-Butadiene Catalyzed by Cobalt(II) Complexes Bearing Α-Diimine Ligands

A series of cobalt(II) complexes bearing α‐diimine ligands were synthesized and characterized by elemental and spectroscopic analysis. These complexes had the general formulas [ArN = C(Me)-(Me)C = NAr]CoCl2 (Ar = C6H5, 3a; 4‐MeC6H4, 3b; 4‐MeOC6H4, 3c; 4‐FC6H4, 3d; 4‐ClC6H4, 3e; 2‐MeC6H4, 3f; 2‐EtC6H4, 3g; 2‐iPrC6H4, 3h; 2, 4, 6‐Me3C6H2, 3i; 2, 6‐Et2C6H3, 3j; 2, 6‐iPrC6H3, 3k). 2,6‐Bis[(2,6‐diisopropylphenylimino)ethyl]pyridine CoCl2 (4a) was also synthesized for comparison. The structures of complexes 3i, 3k, and 4a were further analyzed by X‐ray crystallography. When the Co(II) complexes were activated with ethylaluminum sesquichloride, they exhibited high catalytic activity for 1,3‐butadiene polymerization. The polymers produced have high cis‐1,4 stereoregularity (up to 98.0%) and high molecular weights (Mn = 1×10^4 - 1×10^5). The substituent ligand affected both catalytic activity and stereoselectivity through an electronic effect while steric hindrance by the substituent was not important. The effects of the polymerization conditions, such as polymerization time, temperature, different alkylaluminum compounds used as cocatalyst, and [Al]/[Co] molar ratio, on polymerization behavior were investigated.

In situ X-ray absorption fine structure study on the polymerization of isoprene assisted by Nd-based ternary catalysts

Nd-based ternary catalysts are widely used for the polymerization of isoprene in rubber industry, however structure information during the polymerization of isoprene as well as the catalytic mechanism are still ambiguous. In this paper, the in situ XAFS technique was used to extract the local atomic structure around the Nd center of the catalyst consisting of Nd(vers)3, AlEt3, and Al(iBu)2Cl. Theoretical calculations were used to verify the structure changes in the alkylation process. Four catalysts with different alkylaluminums {AlEt3, Al(nOct)3, Al(iBu)3, and Al(iBu)2H} were, respectively, used for the polymerization of isoprene. The results demonstrate that the substitution of Nd–C for Nd–O bonds is reasonable in the alkylation step. The structural evolutions in the alkylation and chlorination steps, as well as in the polymerization processes of isoprene are all similar for these Nd-based ternary catalysts with different alkylaluminum components. In the polymerization process of isoprene, there are only about 2 Nd–Cl bonds at 2.85 A and 1–2 Nd–C bonds at 2.42 A around the Nd centers which are in a monomer state. The Nd–C bonds can be attributed to the contribution of isoprene. This highly-opened structure of the Nd active centers activates greatly the catalytic activity of the Nd-based ternary catalysts. A conjectural catalytic mechanism for the polymerization of isoprene has been deciphered on the basis of the in situ XAFS results. This study is expected to be helpful for the improvement and application of the Nd-based ternary catalysts.