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Syntheses, Characterization And Norbornene Polymerization Properties Of (benzimidamide)Ni(Ⅱ) And (pyrazole)Ni(Ⅱ) Complexes

Posted on:2014-06-17Degree:MasterType:Thesis
Country:ChinaCandidate:Z W ZhengFull Text:PDF
GTID:2251330422456624Subject:Polymer Chemistry and Physics
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The work of this thesis includes two parts:1.) Vinyl polymerization ofnorbornene(NB) by using (benzimidamide)Ni(II)/MAO catalyst system.2.) Vinyl NBpolymerization by using bis(pyrazole)Ni(II)/MAO catalyst system.1.) Two nickel(II) complexes (Ca, Cb) bearing N-(pyridin-2-yl)benzimidamideligands,[Aryl-N=C(Ph)-NH-2-C5H4N](Ar=2,6-i-Pr2C6H3(La),2,6-Me2C6H3(Lb)),were synthesized and characterized by elemental analysis (EA) and1H NMR. X-raycrystal structure of complexs reveal that the six-numbered chelate ring of bulkyligand complex Ca take a boat conformaiton, meanwhile the chelate ring atoms of lessbulky complex Cb are approximately in a same plane. In the presence of excessmethylaluminoxane (MAO), both complexes showed high activities of106gmolNi-1h-1for norbornene polymerization. The influence of temperature (0~50oC), Al/Ni ratio(200~1000) and the quantity of catalyst on polymerization were investigated. Resultsshow the catalyst activities increased with the increasing of Al/Ni ratio, the optimaleffecience of MAO were found at around Al/Ni ratio of800. The catalytic activity ofCa/MAO and Cb/MAO systems increased with temperature increasing, hightestactivities of them were observed at around10oC, and then their activity decreased withtemperature increasing.1H NMR anylsis show the obtained polymers are vinylicpolynorbornenes (PNBs). Gel permeation chromatography (GPC) results show(benzimidamide)Ni(II)/MAO catalysts gave unimodal polymers (Weight-averagemolecular weight (Mw),2.51-5.13×106g/mol) with relatively narrow molecular weightdistribution (Mw/Mn) of1.68-2.76, indicative of single-site catalyst behavior. At thesame condition (10oC, Al/Ni=800), the activity of less bulky Cb/MAO catalyst canreach3.83×106g(PNB) molNi-1h-1, which is approximately four times higher than thatof bulky Ca/MAO system. This experiment result illustrate the steric group attached to a boat conformation chelate ring can not provide effective protection to real activecenter of catalyst.2.) Four nickel(II) complexes (C1, C2, C3, C4) bearing1-R-3,5-dimethyl-1H-pyrazole ligands (R=phenyl(L1), benzyl(L2),2-methylbenzyl(L3), naphthalen-1-ylmethyl(L4),), were synthesized and characterizedby EA and1H NMR. In the presence of excess MAO, these complexes were used ascatalyst precursors for norbornene polymerization. Results show the catalyst activitiesincreased with the increasing of Al/Ni ratio, the optimal effecience of MAO werefound at around Al/Ni ratio of800. The highest catalytic activities of these catalystswere observed at around20oC, and their activities were found decreasing beyond thistemperature. At optimal polymerization condition, the activity sequence of theabove-mentioned catalysts is C1≈C3>C2>C4. The activities of C1/MAO system arevery sensitive to the temperature variation, while the C3/MAO catalyst showed highactivity of106gmolNi-1h-1level over a wide temperature range from0oC to60oC. GPCresults show (pyrazole)Ni(II)/MAO catalysts gave unimodal polymers (Mw,1.83~5.21×106g/mol) with relatively narrow distribution (Mw/Mn) of1.91~2.97, indicative ofsingle-site catalyst behavior. In optimal polymerization condition (20oC, Al/Ni=800),both C1/MAO and C3/MAO catalysts showed high activities of106gmolNi-1h-1forethylene/norbornene copolymerization. Copolymerization activities and NBconversion rate were found increasing with the increase of NB concentration andNi/NB ratio.
Keywords/Search Tags:(Benzimidamide)Ni(II)/MAO, (pyrazole)Ni(II)/MAO, Norbornenepolymerization, Ethylene/Norbornene copolymerization
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