Copolymerization of β-Pinene and Norbornene with 2-Aminopyridine Nickel(II) Complexes/MAO Catalysts

In the presence of methylaluminoxane (MAO), 2-aminopyridine Ni (II) complexes [(2-PyCH2NAr)NiBr, Ar = 2,6-dimethylphenyl (a), 2, 6-diisopropylphenyl (b), 2,6-difluorophenyl (c)] presented highly catalytic activity for the copolymerizations of p-pinene and norbornene and afforded the copolymers with broad molecular weight distribution(PDI approximate to 3.7-5.5). Complex c exhibited highest catalytic activity for the copolymerization under same conditions. After being extracted by CHCl3 and THF, the crude product could be divided into two fractions with narrow molecular weight distribution(PDI approximate to 2.0), CHCl3-soluble but THF-insoluble fraction and THF-soluble fraction. The former contains high norbornene content (x(N) > 90%) with higher molecular weight and the latter contains high beta-pinene content with lower molecular weight, indicating that there exist two kinds of catalytic species in the copolymerization systems. The TGA analyses of the copolymers show that there are two thermal decomposition stages, and the loss of mass in the low thermal decomposition temperature stage decreases with an increase of norbornene content in the copolymer.