Vinyl-polymerization of norbornene with novel anilido–imino nickel complexes/methylaluminoxane: Abnormal influence of polymerization temperature on molecular weight of polynorbornenes |
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Authors: | Haiyang Gao Junkai Zhang Yan Chen Fangming Zhu Qing Wu |
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Institution: | Institute of Polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-sen (Zhongshan) University, Guangzhou 510275, China |
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Abstract: | Herein reported are investigations of norbornene polymerization by novel anilido–imino nickel complexes (Ar1N CHC6H4NAr2)NiBr]2 (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 with methylaluminoxane (MAO). It was found that at polymerization temperatures below 50 °C, the average molecular weights of the obtained polynorbornenes catalyzed by these four catalytic systems increase with raising temperature, displaying bimodal distribution in GPC curves. The abnormal influence of polymerization temperature could be attributed to the existence of two kinds of catalytic species: heterobimetallic species LNi(II)(μ-Me)2AlMe2 (I) and monometallic species LNi(II)Me (II) (L = anilido–imino ligand) at lower temperature. The former affords a lower molecular weight polymer and the latter higher molecular weight one. With raising polymerization temperature above 50 °C, the species I disappears and only species II exists in polymerization systems, resulting in a normal relation of molecular weight to polymerization temperature. From a kinetic study of the norbornene polymerization catalyzed by 1/MAO catalyst at 70 °C, the polymerization rate (Rp) can be expressed by the formulation: Rp = kNBE]1.93Ni]0.88. Moreover, the mechanism of the norbornene polymerization using the anilido–imino nickel complexes activated with MAO is also presented and discussed. |
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Keywords: | Anilido–imino nickel complexes Norbornene Addition polymerization Polynorbornene |
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