172883-44-2Relevant academic research and scientific papers
Ethylene, styrene, and α-methylstyrene polymerization by mono(pentamethylcyclopentadienyl) (Cp*) complexes of titanium, zirconium, and hafnium: Roles of cationic complexes of the type [Cp*MR2]+ (R = alkyl) as both coordination polymerization catalysts and carbocationic polymerization initiators
Wang, Qinyan,Quyoum, Ruhksana,Gillis, Daniel J.,Tudoret, Marie-José,Jeremic, Dusan,Hunter, Brian K.,Baird, Michael C.
, p. 693 - 703 (2008/10/08)
A variety of monocyclopentadienyl and mono(pentamethylcyclopentadienyl) complexes of titanium, zirconium, and hafnium are assessed for abilities to initiate polymerization of ethylene, styrene, and, in part, α-methylstyrene. In general, little or no activity was found for either neutral species of the types CpMMe3 and CpMMe2OR or for cationic 12- and 14-electron species of the types [CpMR2L]+ and [CpMR2L2]+, respectively (Cp = η5-cyclopentadienyl; R = alkyl; L = amine, phosphine ligands). In contrast, much better olefin polymerization initiators result from abstraction of a methyl carbanion from Cp*MMe3 (Cp* = η5-pentamethylcyclopentadienyl) by B(C6F5)3, a reaction which gives cationic, 10-electron species of the type [Cp*MMe2][BMe(C6F5)3] . Of these, the complex [Cp*TiMe2][BMe(C6F5)3] (A) is an excellent initiator or initiator precursor for the polymerization of ethylene and styrene, resulting in high yields respectively of high molecular weight polyethylene and atactic (a-PS) and/or syndiotactic polystyrene (s-PS), depending on conditions; the tacticity of purified s-PS, as judged by 13C{1H} NMR spectroscopy, approaches 100%. While the polymerization of ethylene probably involves a classical Ziegler-Natta process, polymerization of styrene to s-PS and a-PS apparently involves respectively a Ziegler-Natta process and carbocationic initiation. High yields of essentially syndiotactic poly(α-methylstyrene) are obtained by utilizing the same initiator system, also apparently via a carbocationic process.
