Polymerization of styrene using pyrazolylimine nickel (II)/methylaluminoxane catalytic systems

The polymerization of styrene with two pyrazolylimine nickel (II) complexes of (2-(C3HN2Me2-3, 5)(C(Ph) = N(4-R2C6H2(R1)2-2, 6)NiBr2 (Complex 1, R1 = iPr, R2 = H; Complex 2, R1 = H, R2 = NO2)) activated by methylaluminoxane was studied. The influences of polymerization parameters such as polymerization temperature, Al/Ni molar ratio, and reaction time on catalytic activity and molecular weight of the polystyrene (PS) were investigated in detail. The electron-withdrawing of nitro group in Complex 2 could not enhance the catalytic activity for styrene polymerization; however, the molecular weights of polymers were increased. Both of the two catalytic systems exhibited high activity [up to 8.45 × 105 gPS/(mol Ni h)] for styrene polymerization and provide PS with moderate to low-molecular weights (Mw = 2.21 × 104∼ 5.71 × 103 g/mol) and narrower molecular weight distributions about 2.0. The obtained PS were characterized by means of IR, 1H NMR, and 13C NMR techniques. The results indicated that the PS was atactic polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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