Novel Three-Dimensional Geometry Nickel(Ⅱ) Catalysts With Different Electronic Effects On α-Diimine Bisligands:Synthesis And Catalytic Copolymerization For Norbornene And1-Alkene

Vinyl-addition type polynorbornene (PNB) is an attractive material due to its unique characteristics, such as good heat and chemical resistance, dielectric constants, nonhygroscopicity, and high transparency. So far there are many articles about norbornene(NB) polymerization. However, the PNB’poor processability, solubility and adhesion limit its application. These defects can be improved by copolymerizing with a-alkene. A novel, effectual, stable catalyst and comonomer are two important factors to improve the yield of the polymerization and properties of the polymer. Especially, the designing of new catalyst is very important.Among the catalysts that have been reported for the vinyl polymerization of NB, a-diimine nickel and palladium complexes are the most frequently used catalyst species. To obtained high effective, stable catalyst, a series of three-dimensional geometry nickel(II) catalysts with a-diimine bisligands containing different electronic effects groups(C1=-CH3, C2=-C1, C3=-CF3) were synthesized and characterized. The three-dimensional geometry may enhance the stability of nickel a-diimine complexes by hindering the rotation of aniline moieties and protecting the metal center effectively. The structure of three-dimensional geometry nickel(II) catalysts was determined by X-ray diffraction and catalyzed the norbornene homopolymerization in the presence of B(C6F5)3. All catalysts exhibited high reactivities toward NB homopolymerization(105gpolymer/molNi h).In order to further improve the properties of polynorbornene,1-alkene were selected to copolymerize with NB by the catalyst systen of Ni(II)/B(C6F5)3. Compared with the NB homopolymerization, the Ni(II)/B(C6F5)3exhibited slightly low activity to the copolymerization of NB with1-alkene. The substituent effect on the aryl ring of the catalysts influenced its reactivities. Introduction strong electron-withdrawing group CF3of C3can increase the reactivity. Meanwhile, the obtained copolymers catalyzed by C3/B(C6F5)3exhibited relatively high molecular weights (0.3-1.5×105g/mol) and narrow molecular weight distribution(1.8-2.0). When the comonomer feed ratios were varied from10to50%, the1-alkene content in the copolymers can be controlled up to8.56-14.33%. The copolymers exhibited good thermal stability and better solubility than that of PNB.