Mechanism of olefin polymerization by a soluble zirconium catalyst

✍ Scribed by A.R Siedle; W.M Lamanna; R.A Newmark; J.N Schroepfer

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 323 KB
• Volume: 128
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(97)00179-9

✦ Synopsis

A mechanistic study has been carried out on the homogeneous olefin polymerizationroligomerization catalyst formed Ž . from Cp ZrMe and methylaluminoxane, MeAlO , in toluene. Formal transfer of CH from Zr to Al yields low 2 2 x 3 q wŽ .Ž . x concentrations of Cp ZrMe solvated by Me AlO MeAlO . The cationic Zr species initiates ethylene oligomeriza-2 2 y x yy y tion by olefin coordination followed by insertion into the Zr-CH bond. Chain transfer occurs by one of two competing 3 q Ž . pathways. The predominant one involves exchange of Cp Zr-P P s growing ethylene oligomer with Al-CH to produce 2 3 another Cp ZrMe q initiator plus an Al-bound oligomer. Terminal Al-C bonds in the latter are ultimately cleaved on 2 hydrolytic workup to produce materials with saturated end groups. Concomitant chain transfer occurs by sigma bond metathesis of Cp Zr-P q with ethylene. Metathesis results in cleavage of the Zr-C bond of the growing oligomer to produce 2 materials also having saturated end groups; and a new initiating species, Cp Zr-CH5CH q . The two chain transfer pathways 2 2 afford structurally different oligomers distinguishable by carbon number and end group structure. Oligomers derived from q Ž . q the Cp ZrMe channel are C n s odd alkanes; those derived from Cp Zr-CH5CH are terminally mono-unsaturated 2 n 2 2

Ž . C n s even alkenes. Chain transfer by beta hydride elimination is detectable but relatively insignificant under the n conditions employed. Propylene and 1-hexene react similarly but beta hydride elimination is the predominant chain transfer step. The initial Zr-alkyl species produces a Cp ZrH q complex that is the principle chain initiator. Chain transfer is fast 2 relative to propagation and the products are low molecular weight oligomers. q 1998 Elsevier Science B.V.