Vinyl polymerization of norbornene with pyrazolylimine nickel(II)/methylaluminoxane catalytic systems

The polymerization of norbornene (NBE) was investigated in the presence of two novel pyrazolylimine nickel complexes [2‐(C 3 HN 2 Me 2 ‐3,5){C(Ph)[4‐R 2 C 6 H 2 (R 1 ) 2 ‐2,6]}NiBr 2 (complex 1, R 1 = i Pr and R 2 = H; complex 2, R 1 = H and R 2 = NO 2 )] activated by methylaluminoxane. The two catalytic systems showed high activity [up to 1.27 × 10 6 g of polynorbornene (PNBE)/(mol of Ni h)] for NBE polymerization and provided PNBEs with high molecular weights (weight‐average molecular weight ≤ 17.46 × 10 5 g/mol) and narrow molecular weight distributions (ca. 2). The electron withdrawing of the nitro group in complex 2 could not enhance the catalytic activity for NBE polymerization; however, the molecular weights of the polymers were increased. The catalytic activity, molecular weight, and molecular weight distribution were influenced by the polymerization conditions, such as the polymerization temperature and Al/Ni molar ratios. The obtained PNBEs were characterized by means of 1 H‐NMR and Fourier transform infrared spectroscopy techniques. The analysis results for PNBEs indicated that the NBE polymerization was a vinyl‐type polymerization rather than a ring‐opening metathesis polymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008