Controlled Isospecific Polymerization of 伪-Olefins by Hafnium Complex Incorporating with a trans-Cyclooctanediyl-Bridged [OSSO]-Type Bis(phenolate) Ligand

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• 作者：Norio Nakata ; Tomoyuki Toda ; Tsukasa Matsuo ; Akihiko Ishii
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：September 10, 2013
• 年：2013
• 卷：46
• 期：17
• 页码：6758-6764
• 全文大小：321K
• 年卷期：v.46,no.17(September 10, 2013)
• ISSN：1520-5835

文摘

Treatment of trans-cyclooctanediyl-bridged [OSSO]-type ligand 1 with Hf(CH₂Ph)₄ in toluene afforded the corresponding hafnium(IV) dibenzyl complex 5 as pale yellow crystals. X-ray crystallographic analysis of 5 revealed that the six-coordinated hafnium center incorporated in the [OSSO]-type ligand 1 adopted cis-伪 configuration, and two benzyl ligands were coordinated to hafnium center by 畏¹-fashion. In the polymerization of 1-hexene, the combination of hafnium complex 5 and B(C₆F₅)₃, (Ph₃C)[B(C₆F₅)₄], or dMAO (dried methylaluminoxane) as an activator provided poly(1-hexene)s with perfect isotacticity ([mmmm] > 95%) and high molecular weights (M_w = 74鈥?00鈥?21鈥?00 g mol^鈥?). The combination of 5/dMAO catalyst system, in particular, exhibited fairly high activity of 2100 g mmol (5)^鈭? h^鈥?, which is quite higher than those of previously reported [OSSO]-type hafnium complexes. In addition, the polymerization of 4-methyl-1-pentene (4-MP) catalyzed by the 5/(Ph₃C)[B(C₆F₅)₄] system at room temperature produced completely isotactic poly(4-MP)s with good activity (54鈥?01 g mmol (5)^鈭? h^鈥?) and relatively narrow PDI (M_w/M_n = 1.3). Furthermore, the propylene polymerization catalyzed by the 5/dMAO system at different temperatures (0鈥?0 掳C) for 1 h afforded highly isotactic polypropylenes, where the catalyst activity and isotacticity depend on the polymerization temperature. Thus, the activity greatly increased from 500 to 17鈥?00 g mmol (5)^鈭? h^鈥? when the polymerization temperature was increased. In contrast, isotacticity and melting transition temperature (T_m) were elevated by decreasing polymerization temperature (at 0 掳C: [mmmm] = 93.7%, T_m = 156.2 掳C; at 70 掳C: [mmmm] = 86.8%, T_m = 140.9 掳C).