Vinyl-Addition Polymerization of Norbornene Catalyzed by Chelating (Pyridyl)imine Metal Complexes

Polynorbornene is a versatile polymer for preparing high-performance materials such as membranes for gas separation, micro- and optoelectronics, fuel cells, sensors, and catalysts. It is therefore significant to design low-cost and high-performance catalysts for the syntheses of polynorbornene. In this work, a number of Schiff-base metal complexes ligated on proligands N-(1-phenylethyl)-1-(pyridin-2-yl)methanimine (L1) and 1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanimine (L2); [Ni(L1)(2)Cl-2] (Ni1), [Pd(L1)Cl-2] (Pd1), [Fe(L1)(3)]2[PF6] (Fe1), [Co(L1)(3)]2[PF6] (Co1), [Ni(L2)Cl-2] (Ni2), [Fe(L2)Cl-2] (Fe2), and [Co(L2)Cl-2] (Co2) were used as catalysts in the polymerization of norbornene. The Ni(II) complexes exhibited the highest catalytic activities when compared to the Fe(II) and Co(II) complexes. Higher catalytic activities were recorded in non-polar solvents (toluene and chlorobenzene), compared to the polar CH2Cl2 solvent. Sterically bulky Ni(II) catalysts produced polymers with high molecular weights. Ni1 produced polymers with the highest glass transition temperatures (T-g) of up to 302 degrees C and M-w of 1,180,000 g mol(-1). The nature of the ligand backbone, coordination chemistry of the complexes, and reaction conditions largely controlled both the catalytic activities and the polymer microstructure.