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Elastomeric polypropylene from unbridged bis(2-arylindenyl) metallocenes :Investigation of the mechanism of stereoblock polypropylene formation

Record Type:	Electronic resources : Monograph/item
Title/Author:	Elastomeric polypropylene from unbridged bis(2-arylindenyl) metallocenes :
Reminder of title:	Investigation of the mechanism of stereoblock polypropylene formation
Author:	Wilmes, Gregg Michael.
Description:	161 p.
Notes:	Adviser: Robert M. Waymouth.
Notes:	Source: Dissertation Abstracts International, Volume: 64-11, Section: B, page: 5551.
Contained By:	Dissertation Abstracts International64-11B.
Subject:	Chemistry, Polymer.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3111823
ISBN:	0496593536

Elastomeric polypropylene from unbridged bis(2-arylindenyl) metallocenes :Investigation of the mechanism of stereoblock polypropylene formation
Wilmes, Gregg Michael.

Elastomeric polypropylene from unbridged bis(2-arylindenyl) metallocenes :Investigation of the mechanism of stereoblock polypropylene formation [electronic resource] - 161 p.

Adviser: Robert M. Waymouth.

Thesis (Ph.D.)--Stanford University, 2004.

A series of unbridged bis(2-arylindenyl)zirconocenes varying both in the pi indenyl ligand framework and the sigma ligand was synthesized. The rotation rates of the dimethyl-substituted metallocenes were too fast to be determined by standard NMR techniques. On-resonance spin lattice relaxation in the rotating frame (T1rho) was used to determine the rate of rotation of the aryl ligands in the dimethyl species. The nature of both the sigma and the pi ligand systems affects the rate with sterically bulky substituents resulting in slower rotation. The effect of the sigma ligand is substantially stronger than that of the pi ligand.

ISBN: 0496593536Subjects--Topical Terms:

227045
Chemistry, Polymer.

Elastomeric polypropylene from unbridged bis(2-arylindenyl) metallocenes :Investigation of the mechanism of stereoblock polypropylene formation
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245 1 0 $a Elastomeric polypropylene from unbridged bis(2-arylindenyl) metallocenes : $b Investigation of the mechanism of stereoblock polypropylene formation $h [electronic resource]
300 $a 161 p.
500 $a Adviser: Robert M. Waymouth.
500 $a Source: Dissertation Abstracts International, Volume: 64-11, Section: B, page: 5551.
502 $a Thesis (Ph.D.)--Stanford University, 2004.
520 # $a A series of unbridged bis(2-arylindenyl)zirconocenes varying both in the pi indenyl ligand framework and the sigma ligand was synthesized. The rotation rates of the dimethyl-substituted metallocenes were too fast to be determined by standard NMR techniques. On-resonance spin lattice relaxation in the rotating frame (T1rho) was used to determine the rate of rotation of the aryl ligands in the dimethyl species. The nature of both the sigma and the pi ligand systems affects the rate with sterically bulky substituents resulting in slower rotation. The effect of the sigma ligand is substantially stronger than that of the pi ligand.
520 # $a Propylene polymerizations in liquid propylene by bis(2-phenylindenyl)zirconium dimethyl activated by MAO, trityl tetrakis(pentafluorophenyl)borate, dimethylanilinium tetrakis(pentafluorophenyl)borate, or tris(pentafluorophenyl)borane (B(C 6F5)3) revealed a significant influence of cocatalyst on the polymerization behavior of these catalysts. The productivity and stereoselectivity of the catalyst systems were highest with MAO and lowest with B(C6F 5)3, with B(C6F5)3 yielding amorphous atactic polypropylenes. The presence of aluminum isobutyl groups, either on MAO or from added triisobutylaluminum, increased the stereoselectivity of the polymerizations; the polarity had little influence on the stereoselectivity.
520 # $a The sterically hindered metallocene bis(2-(3,5-di-tert-butylphenyl)indenyl)zirconium dichloride produced polypropylenes of much higher isotacticity than did bis(2-phenylindenyl)zirconium dichloride. Lower-tacticity polypropylenes generated with the sterically hindered compound contained a high percentage of [mmrm] stereoerrors, indicative of a stereoblock microstructure comprised of isotactic stereosequences of opposite relative configuration. Bis(2-(3,5-di-tert-butylphenyl)indenyl)hafnium dichloride produced polypropylenes of moderate tacticity and did not show a drop in productivity or stereocontrol with increasing temperature.
520 # $a Unbridged group 4 bis(2-arylindenyl)metallocenes are active catalysts for the formation of elastomeric stereoblock polypropylene when activated by a cocatalyst, typically methylaluminoxane (MAO). Careful mechanistic studies of these catalyst systems are compromised by the ill-defined nature of MAO. Well-defined stoichiometric cocatalysts leading to boron-based counteranions have here been used for polymerization and NMR studies.
520 # $a Variable temperature NMR studies of bis(2-arylindenyl)zirconium dimethyl compounds activated by B(C6F5)3 showed dynamic behavior consistent with fast ligand rotation and slower rearrangement of the ion pairs. Model compounds of the cationic active species were synthesized, and the conformation of the pi-ligand framework could be influenced to give a Cs-symmetric syn isomer of the metallocene.
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