The origin of the syndiotactic selectivity in propene polymerization of a typical bridged fluorenyl amido catalyst, namely [Me2Si(3,6-di-tert-butyl-9-fluorenyl)(N-tert-butyl)]TiCl2 (1), activated with methylaluminoxane or [HMe2N(C6H5)][B(C6F5)(4)]/Al(i-butyl)(3), was investigated by means of 150 MHz C-13 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.
Syndiotactic Poly(propylene) from [Me2Si(3,6-di-tertbutyl-9-fluorenyl)(N-tert-butyl)]TiCl2–Based Catalysts: Chain-End or Enantiotopic-Sites Stereocontrol? / Busico, V; Cipullo, R; Cutillo, F; Talarico, Giovanni; Razavi, A.. - In: MACROMOLECULAR CHEMISTRY AND PHYSICS. - ISSN 1022-1352. - STAMPA. - 204:(2003), pp. 1269-1274. [10.1002/macp.200390095]
Syndiotactic Poly(propylene) from [Me2Si(3,6-di-tertbutyl-9-fluorenyl)(N-tert-butyl)]TiCl2–Based Catalysts: Chain-End or Enantiotopic-Sites Stereocontrol?
CIPULLO R;TALARICO, GIOVANNI;
2003
Abstract
The origin of the syndiotactic selectivity in propene polymerization of a typical bridged fluorenyl amido catalyst, namely [Me2Si(3,6-di-tert-butyl-9-fluorenyl)(N-tert-butyl)]TiCl2 (1), activated with methylaluminoxane or [HMe2N(C6H5)][B(C6F5)(4)]/Al(i-butyl)(3), was investigated by means of 150 MHz C-13 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.