Room-temperature polymerization of ¦Â-pinene by niobium and tantalum halides

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• 作者：Mohammad Hayatifar ; Fabio Marchetti ; Guido Pampaloni ; Yogesh Patil ; Anna Maria Raspolli Galletti
• 关键词：¦Â-Pinene ; Cationic polymerization ; Lewis acids ; Niobium halides ; Tantalum halides
• 刊名：Catalysis Today
• 出版年：2012
• 出版时间：30 September, 2012
• 年：2012
• 卷：192
• 期：1
• 页码：177-182
• 全文大小：286 K

文摘

The easily accessible niobium pentahalides NbX₅ (X = F, 1a; X = Cl, 1b; X = Br, 1c) and the tantalum TaF₅ (2a) were applied for the first time as effective catalysts for the synthesis of poly-¦Â-pinene at room temperature, adopting low catalyst content (0.6 mM). ¹H NMR analyses indicated that the produced ¦Â-pinene polymers were structurally identical to that formed by conventional cationic Lewis acid initiators. Niobium pentachloride gave low molecular weight (M_n = 1200-1600) polymer with high conversion degree. The effects of the main reaction parameters (i.e. solvent, temperature, catalyst concentration, time and eventual co-catalysts) on the NbCl₅-promoted polymerization were investigated. Polymerization quenching with methanol resulted in the incorporation of a methoxy-end group into the polymer chain, thus confirming a cationic mechanism. On the other hand, NbI₅, TaCl₅, the carbamato-complexes M(O₂CNEt₂)₅ (M = Nb, Ta) and the mononuclear adducts NbX₅L [X = Cl, L = MeCN, Ph₂CO or (NMe₂)₂CO; X = F, L = EtOH] were not active in ¦Â-pinene polymerization.