Substituent effects of tert-butyl groups on fluorenyl ligand in syndiospecific living polymerization of propylene with ansa-fluorenylamidodimethyltitanium complex

摘要

[t-BuNSiMe2(2,7-t-Bu(2)Flu)]TiMe2 and [t-BuNSiMe2(3,6-t-Bu(2)Flu)]TiMe2 were synthesized and characterized by elemental analysis, H-1 NMR, and single-crystal X-ray analysis. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMNIAO) as a cocatalyst at 0 and 25 degrees C. The introduction of tert-butyl substituents to the fluorenyl ligand improved the activity more than 3 times regardless of the position of the substituents. The postpolymerization testified that both catalytic systems conducted the propylene polymerization in a living manner at both 0 and 25 degrees C. The propagation rate increased linearly against the Al/Ti ratio from the range of 100-400 with keeping the number of polymer chains constant, which directly indicates that a larger amount of dMMAO enhanced the propagation rate. The introduction of tert-butyl substituents also improved the syndiospecificity: the 3,6-position was more effective than the 2,7-position, and [t-BuNSiMe2(3,6-t-Bu(2)Flu)]TiMe2 gave the living polypropylene with the syndiotactic triad of 0.93 and the melting point of 142 degrees C.