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Syndiotactic Poly(propylene) from [Me 2 Si(3,6‐di‐ tert ‐butyl‐9‐fluorenyl)( N ‐ tert ‐butyl)]TiCl 2 –Based Catalysts: Chain‐End or Enantiotopic‐Sites Stereocontrol?
Author(s) -
Busico Vincenzo,
Cipullo Roberta,
Cutillo Francesco,
Talarico Giovanni,
Razavi Abbas
Publication year - 2003
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200390095
Subject(s) - methylaluminoxane , tacticity , catalysis , polymer chemistry , polymerization , chemistry , propene , polymer , organic chemistry , metallocene
The origin of the syndiotactic selectivity in propene polymerization of a typical bridged fluorenyl‐amido catalyst, namely [Me 2 Si(3,6‐di‐ tert ‐butyl‐9‐fluorenyl)( N ‐ tert ‐butyl)]TiCl 2 ( 1 ), activated with methylaluminoxane or [HMe 2 N(C 6 H 5 )][B(C 6 F 5 ) 4 ]/Al( i ‐butyl) 3 , was investigated by means of 150 MHz 13 C NMR spectroscopic microstructural polymer analysis. The asymmetric induction was traced unambiguously to enantiotopic‐sites control. Compared with the better‐known cyclopentadienyl‐fluorenyl ansa ‐zirconocenes, 1 turned out to be almost identically enantioselective (in agreement with computer modeling), but less stereoselective because of a higher propensity to undergo site epimerization. This results in a chain microstructure with large predominance of m over mm stereodefects, deceptively similar to that of syndiotactic poly(propylene) produced under chain‐end control.Methyl region of the 150 MHz 13 C NMR spectrum of a poly(propylene) sample prepared with catalyst system 1 /borate/TIBAl.