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madeli111銀蟲 (小有名氣)
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Living polymerization techniques1 allow the synthesis of polymers with predictable molecular weights and narrowmolecular weight distributions, end-functionalized polymers andwell-defined block copolymers. While intense efforts haverecently focused on development of homogeneous single-site,early metal d0 and d0fn catalysts for polymerization of ethyleneand R-olefins (particularly propylene),2 rapid chain transferprocesses in these systems have limited their use as iving polymerization catalysts. The living polymerization of R-olefins has been achieved only in rare instances and at very low temperatures.3,4 We describe here the development of a procedurefor living polymerization of R-olefins based on recently reported NiII-R-diimine catalysts5 and application of this procedure to the synthesis of diblock and triblock poly(R-olefins). Access to well-defined transition metal olefin polymerizationcatalysts has allowed detailed mechanistic studies of this importantclass of catalysts. While much attention has centered on earlytransition metal d0 and lanthanide d0fn systems,1-7 we have focusedon developing single-site late metal catalysts. Our initial report8 that Ni(II) and Pd(II) aryl-substituted R-diimine complexes bearing bulky ortho substituents were capable of polymerizing ethyleneand R-olefins has stimulated extensive experimental9-20 andtheoretical21-27 work on these catalysts. The Pd(II) systems yield highly branched polyethylene under typical polymerization conditions,while the microstructure of polyethylene produced by theNi(II) systems is dependent on monomer concentration, reactiontemperature, and ligand structure. |
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zhangzws
金蟲 (正式寫手)
- 翻譯EPI: 41
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- 金幣: 1058.5
- 散金: 15
- 帖子: 355
- 在線: 115.3小時
- 蟲號: 736112
- 注冊: 2009-03-31
- 性別: GG
- 專業(yè): 能源化工
madeli111(金幣+4, 翻譯EPI+1): 2010-09-17 07:49:33
| 活性聚合技術(shù)允許1：具有可預測分子量和窄分子分布的聚合物，端基官能團化聚合物以及精確結(jié)構(gòu)共聚物的合成，然而，最近更多的努力集中在早期均相單點d0和d0fn催化劑的發(fā)展，這一催化劑用于乙烯和R-烯烴的合成，特別是丙烯合成；2：系統(tǒng)中快速鏈轉(zhuǎn)移過程限制了它們作為活性聚合催化劑的作用。R-烯烴的活性聚合僅在極少的情況下和很低的溫度獲得成功。3，4：這里描述了基于最近報道的NiII-R-二亞胺催化劑的R-烯烴活性合成的發(fā)展和這一過程在雙嵌段共聚物和三嵌段共聚物的應用。 |
2樓2010-09-16 21:12:47
zhangzws
金蟲 (正式寫手)
- 翻譯EPI: 41
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- 金幣: 1058.5
- 散金: 15
- 帖子: 355
- 在線: 115.3小時
- 蟲號: 736112
- 注冊: 2009-03-31
- 性別: GG
- 專業(yè): 能源化工
madeli111(金幣+4): 2010-09-17 07:49:41
| 為了獲得結(jié)構(gòu)精確的過渡金屬烯烴聚合催的方法，這類重要催化劑已經(jīng)被進行了詳細的機理研究。然而，也有大量的注意力被集中于早期過渡金屬d0和鑭系元素d0fn，同時我們也一直在關(guān)注單點陣金屬催化劑。我們前期的研究指出： Ni(II) 和 Pd(II)芳基取代R-二亞胺絡合物已經(jīng)廣泛地被用于這些催化劑的實驗和理論研究，其中臨位聚合物具有聚合乙烯和R-烯烴的能力。Pd(II)系統(tǒng)使典型聚合條件下的高壓聚乙烯具有高的產(chǎn)率，然而，由Ni(II)催化劑系統(tǒng)制備的聚乙烯的微孔結(jié)構(gòu)取決于單元結(jié)構(gòu)、反應溫度和配體結(jié)構(gòu)。 |
3樓2010-09-16 21:38:01
zhangzws
金蟲 (正式寫手)
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- 在線: 115.3小時
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- 注冊: 2009-03-31
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4樓2010-09-16 21:40:03
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