Styrene polymerization with novel anilido-imino nickel complexes/MAO catalytic system: Catalytic behavior, microstructure of polystyrene and polymerization mechanism

The polymerization of styrene with novel catalytic systems of anilido-imino nickel complexes (Ar¹N = CHC₆H₄NAr²) NiBr (Ar¹ = Ar² = 2,6-dimethylphenyl, 1; Ar¹ = 2,6-dimethylphenyl, Ar² = 2,6-diisopropylphenyl, 2; Ar¹ = Ar² = 2,6-diisopropylphenyl, 3; Ar¹ = 2,6-diisopropylphenyl, Ar² = 2,6-dimethylphenyl, 4) activated by methylaluminoxane was investigated. The influence of reaction parameters (temperature, Al/Ni mole ratio, and polymerization time) on styrene polymerization was evaluated. The influence of the bulkiness of the substituents on polymerization activity and polymer characteristics was also ascertained. The obtained polystyrene was an iso-rich atactic polymer and its weight-average molecular weight reached 70 500. NMR analysis of the end groups further confirmed that styrene polymerization catalyzed by anilido-imino nickel complexes/MAO systems proceeded through a coordination mechanism, and the chain was initiated through styrene secondary insertion into the NiH and terminated mainly through β-H elimination of styrene producing the chain-end group (CHCHPh).