Correlation between catalyst surface structure and polypropylene tacticityin Ziegler-Natta polymerization system

Citation
Sh. Kim et Ga. Somorjai, Correlation between catalyst surface structure and polypropylene tacticityin Ziegler-Natta polymerization system, J PHYS CH B, 105(18), 2001, pp. 3922-3927
Citations number
47
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
105
Issue
18
Year of publication
2001
Pages
3922 - 3927
Database
ISI
SICI code
1520-6106(20010510)105:18<3922:CBCSSA>2.0.ZU;2-6
Abstract
correlation between the surface structure of the Ziegler-Natta catalysts an d the stereospecificity in propylene polymerization was shown experimentall y using model catalysts and temperature-programmed desorption (TPD) of mesi tylene as a nondestructive surface probe. Two types of titanium chloride mo del catalysts, with MgCl2 support (TiClx/MgCl2) and without MgCl2 (TiCly), were fabricated on an Au substrate in ultrahigh vacuum. Once activated with AIEt(3) vapor, both catalysts were active for propylene polymerization in the absence of excess ALEt(3) during polymerization. The TiClx/MgCl2 cataly st produced both atactic and isotactic polypropylene, while the TiCly catal yst without the MgCl2 support produced exclusively isotactic polypropylene. For the same catalysts, the mesitylene TPD revealed that TiClx/MgCl2 had t wo adsorption site structures, a basal plane structure and a nonbasal plane structure, while TICly had only the latter structure. To our knowledge, th is was the first direct experimental evidence revealing the structural diff erence of the catalyst surfaces that exhibit different stereospecificity in propylene polymerization.