A series of 2-aminopyridine Ni(II) complexes bearing different substituent groups {(2-PyCH2NAr)NiBr

Ar=2

6-dimethylphenyl (a)

Ar=2

6-diisopropylphenyl (b)

Ar=2

6-difluorophenyl (c)} have been synthesized.In the presence of methylaluminoxane (MAO)

these Ni complexes could be highly efficient to catalyze β-pinene polymerization and afforded poly(β-pinene)s with higher molecular weight than those prepared by traditional cation polymerizations.Among these complexes

complex c with ortho-electroattracting-substitution exhibited the highest catalytic activity up to 1.48×107g/(molNi#12539;h)

while complex b with bulky ortho-isopropyl-substitution gave the highest molecular weight of the polymer.The effects of polymerization conditions on the catalytic activity and the molecular weight of poly(β-pinene)s were also studied.With an increase in temperature

the catalytic activity increased and reached a maximum value at 40～50℃

and the molecular weight of the obtained polymer decreased.Increasing in monomer concentration

molar ratio of MAO to the Ni complexes or decreasing in Ni complex concentration would increase the catalytic activity for β-pinene polymerization.The 1H-NMR and 13C-NMR analyses of the obtained polymers revealed that the polymers consisted of alternating sequences of isobutylene and cyclohexene units

indicating the propagation proceeded in a manner typical for conventional carbocationic polymerization process.