Abstract:
Three bis-(salicylaldiminato) nickel (Ⅱ) complexes with different steric hindrances on the adjacent position of aniline group,O-(3,5-I
2)C
6H
3-
o-C(H)=N-2,6-C
6H
3(Me)
22Ni (
C1),O-(3,5-I
2)C
6H
3-
o-C(H)=N-2,6-C
6H
3(Et)
22Ni (
C2) andO-(3,5-I
2)C
6H
3-
o-C(H)=N-2,6-C
6H
3(i-Pr)
22Ni (
C3), were successfully synthesized based on the reaction of Ni(CH
3COO)
2·4H
2O with ligands
L1-L3, HO-(3,5-I
2)C
6H
2-
o-C(H)=N-2,6-C
6H
3(Me)
2(
L1), HO-(3,5-I
2)C
6H
2-
o-C(H)=N-2,6-C
6H
3(Et)
2(
L2) and HO-(3,5-I
2)C
6H
2-
o-C(H)=N-2,6-C
6H
3(i-Pr)
2(
L3). The ligands were characterized by
1H-NMR and FT-IR, and the formed complexes were characterized by
1H-NMR, FT-IR, element analysis (EA) and mass spectrometry (MS). The complexes were applied for copolymerization of ethylene and methyl methacrylate (MMA) in the presence of methylaluminoxane (MAO). The effects of different polymerization factors, such as Al、Ni molar ratio (
nAl/
nNi), catalyst dosage, polymerization reaction temperature and ethylene pressure, the concentration of MMA and polymerization reaction time were investigated systematically. The optimum polymerization conditions were as follows:
nAl/
nNi 150, 25℃, ethylene pressure of 2 MPa and 2 h polymerization. With the increase of
nAl/
nNi, the catalyst activity first increased and then decreased. The more catalyst dosage uses, the higher molecule mass was obtained. The activity increased with the increasing of polymerization pressure. The increases of polymerization time led to an increase followed by a decrease of catalyst activity. The complexes
C1-C3 were evaluated for the copolymerization under the optimum polymerization conditions. The complex
C1 with small substituents on the adjacent position of aniline group displayed higher catalytic activity of 12.2 kg/(mol·h), but lower molecular mass of 5.97×10
5. While
C2 and
C3 with bulky substituents on the adjacent position of aniline group showed low catalytic activity, 6.8 kg/(mol·h) and
C3 5.4 kg/(mol·h) respectively, and high molecular mass with 8.06×10
5 for
C2 and 9.85×10
5 for
C3. The microstructures of the obtained polymers were characterized by
1H-NMR,
13C-NMR and FT-IR spectra, demonstrating that the polymers were the copolymers of ethylene and MMA.