ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The stereorigid ansa-metallocene catalysts [2,4-cyclopentadien-1-ylidene(isopropylidene)-fluoren-9-ylidene]zirconium dichloride/methylaluminoxane (iPr[FluCp]ZrCl2/MAO) and [(dimethylsilylene)bis(η5-inden-1-ylidene)]zirconium dichloride/methylaluminoxane (Me2Si[Ind]2-ZrCl2/MAO) are different in respect to the symmetry and, therefore, to the behaviour of the stereospecifity, in the size of the angle between the planes of the π-ligand systems and in the homopolymerization behaviour of ethylene and propene. The present paper concerns itself with comparing the investigations of the ethylene/α-olefin and the ethylene/cycloolefin copolymerization with both catalyst systems. The main kinetic result for both catalysts is that the α-olefins show an accelerating effect on the ethylene polymerization rate during the copolymerization whereas norbornene shows exclusively a rate-decreasing effect. The acceleration effect can be explained by an increase in the concentration of active centres and/or an increase of the rate constant of the ethylene insertion. The analysis of the microstructures of the formed copolymers by the use of statistical models demonstrates that in copolymers with a high content of α-olefins, the experimental trial distributions can only be described satisfactorily with second-order Markovian statistics. That means that in this case the last two monomers have influence on the insertion of the subsequent monomer. A further main result of all investigated copolymerizations is that the r-parameters for the α-olefin insertion are more favourable for the system iPr[FluCp]ZrCl2/MAO than for the system Me2Si[Ind]2ZrCl2/MAO; the reason for this is the different size in the coordination gap aperture of the π-ligands. Furthermore, the r-parameters show only a small dependence on the chain length of the α-olefin. Finally, it is remarkable that the stereospecifity (syndiotactic or isotactic α-olefin blocks) remains intact in the copolymers.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1993.021941120
Permalink