Methylaluminoxane heterogenization

Methylaluminoxane-activated zirconocenes were first reported to exhibit extraordinarily high activities in ethylene polymerisation, much higher than those of heterogeneous catalysts, and retained over prolonged periods of time. The productivity of the zirconocene-methylaluminoxane catalysts, which were... 

Table 4.3 Polymerisation of styrene using various heterogeneous titanium-based catalysts activated with methylaluminoxane 1...

In the case of chlorine-free catalysts such as Mg(OH)2/Ti(OBu)4—[A1 (Me)0]x and Si02/Ti(0Bu)4—[Al(Me)0]x, heterogeneous species are assumed to promote the syndiospecific polymerisation of styrene [67,68]. In a polymerisation system with the latter catalyst, best results were achieved when treating the carrier with [AI(Mc)0]x prior to supporting Ti(OBu)4 (no further activation with methylaluminoxane was needed). The polymerisation rate reaches a maximum at an Al/Ti molar ratio of 20 this is much lower than the value of the Al/Ti molar ratio required to reach the maximum polymerisation rate in the respective homogeneous system, i.e. the system without a carrier [54]. 

The discoveries by Kaminsky and Sinn that Group 4 metallocenes in the presence of methylaluminoxane were extremely active for olefin polymerization35,36 caused a considerable resurgence of interest in the application of homogeneous catalysts for olefin polymerization. Surprisingly perhaps, the modification of group IV metallocenes to produce catalysts capable of isospecific polymerization developed more slowly than that of the heterogeneous catalysts by Natta, but has recently seen dramatic success. 

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