ISSN:
0887-624X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Bis(neomenthyl cyclopentadienyl)zirconium dichloride/methyl aluminoxane (η5-(NMCp)2ZrCl2/MAO) catalyst has been investigated for ethylene polymerization. About 51% of the Zr forms active sites more or less instantaneously according to quenching with tritiated methanol. There is an initial drop of rate of polymerization, Rp, of about 30% which remains constant thereafter. The catalytic activity increases monotonically with temperature; it is proportional to [MAO]1.75 at a constant [Zr] = 1.5 μM and proportional to [Zr]-1.2 at a constant [MAO] = 64.5 mM. At very large [MAO]/[Zr], the catalyst has extremely high activity; κp = 5 × 103 (Ms)-1 at 50°C. There is also facile chain transfer to aluminum, κtrA = 0.14 s-1 at 50°C. Both κp and κtrA are about 30 times greater than the corresponding rate constants for MgCl2 supported TiCl3 catalysts. The TiCl3/MgCl2 and (NMCp)2/MAO catalysts have nearly the same activation energy for propagation (ca. 7 kcal/mol-1). The higher activity of the latter is due to its larger preexponential factor in κp. The dependence of catalytic activity on the [MAO]/[Zr] ratio may be explained by rapid association-dissociation equilibria of MAO involving acid-base and/or electron deficient bridge complexation.
Zusätzliches Material:
6 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pola.1988.080260910
Permalink
