ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The syndiotactic propene polymerization was investigated by means of the Cs-symmetric isopropylidene(fluorenyl)(cyclopentadienyl)zirconium dichloride/methylaluminoxane (iPr(Flu)-(Cp)ZrCI2/MAO) catalyst system in toluene/methylene chloride solvent mixtures. The main result is that with increasing dielectric constant of the solvent mixture the polymerization rate increases linearly but the stereospecificity of the catalyst decreases strongly; this is revealed through a drastic decay of the rrrr-pentads and of the melting point of the polymers. Hence, the stereospecificity of this catalyst system is connected with the existence of a polarized Zr-CI-AI-complex (in toluene) or at least of a tight contact ion pair with a stereoregulating role of the counter ion. The loss of the stereospecifity in polar solvents is caused by an isomerization reaction of the solvent-separated free zirconocene species via migration of the growing polymer chain before the next monomer insertion. But in the case of the isotactic catalyst system dimethyl-silyl(bisindenyl)zirconium dichloride/methylaluminoxane (Me2Si(Ind)2ZrCl2/MAO) with a C2-symmetric π-ligand system the migration of the growing polymer chain in polar solvents causes no isomerization.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1992.021930324
