Synthesis and characterization of ethylene-propylene copolymer and polyethylene using a-diimine nickel catalysts

摘要

Nickel-based catalysts of dibromo[N,N'-bis (2,6-diisopropylphenyl)-2,3- butanediimine]nickel(II) (A) and dibromo[N,N'-(phenanthrene-9,10-diylidene) bis(2,6- diisopropylaniline)]nickel(II) (B) were synthesized under controlled conditions. The catalysts A, B and mixed of 1:1 weight ratio of them were used for ethylenepropylene (EP) copolymerization and ethylene polymerization. Methylaluminoxane (MAO) was used as a cocatalyst. The polymers were characterized by means of FT-IR, 1H NMR and DSC (Differential scanning calorimetry). In ethylene polymerization using mixed of 1:1 w/w of the catalysts A and B degree of branching polymer chain decreased with increasing monomer pressure while increased with enhancing polymerization temperature. In ethylene-propylene copolymerization using mixed of 1:1 w/w of A and B, the catalytic system showed the maximum activity at about [Al]/[Ni]02000:1 ratio and further addition of MAO did not affect the activity of the catalyst. Increasing the copolymerization temperature from 20 to 80 °C decreased the productivity of the catalytic system while increased the ethylene content of the copolymer. Decreasing relative pressure of PPr/PEt from 9:1 to 1:1 increased the ethylene contents of the copolymers from 51 % to 72 % while decreased the viscosity average molecular weight (Mv) and glass transition temperature (Tg) of the products. A copolymer with more rubber-like behavior was obtained in relative pressure of PPr/PEt (5:1) and total pressure of 5 bars.