Degenerative transfer living Ziegler-Natta polymerization: application to the synthesis of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length

Journal of the American Chemical Society
Yonghui ZhangLawrence R Sita

Abstract

The neutral dimethyl pentamethylcyclopentadienylzirconium acetamidinate, (eta(5)-C(5)Me(5))ZrMe(2)[N(t-Bu)C(Me)N(Et)], can serve as a highly active initiator for the living Ziegler-Natta polymerization of alpha-olefins to produce polyolefins of narrow polydispersity (D < or = 1.05) when "activated" through mono demethylation by a substoichiometric amount of the borate, [PhNMe(2)H][B(C(6)F(5))(4)]. The mechanism by which this living polymerization proceeds is through a process of degenerative transfer involving rapid and reversible methyl group exchange between cationic (active) zirconium propagating centers and neutral (dormant) methyl, polymeryl zirconium end groups. Facile metal-centered epimerization of the dormant species is responsible for a loss of stereocontrol during propagation that produces iso-rich material in contrast to the pure isotactic polymer microstructure obtained when degenerative transfer is not present. By turning degenerative transfer "on" and "off" between successive monomer polymerizations, a successful strategy for the production of monomodal stereoblock polyolefins of narrow polydispersity and tunable block length has been demonstrated.

Citations

Aug 21, 2015·Nature Chemistry·Amit A Nagarkar, Andreas F M Kilbinger
Feb 23, 2007·Chemistry : a European Journal·Rhett Kempe
Apr 15, 2010·Chemistry, an Asian Journal·Zhibin Guan
Dec 22, 2009·Dalton Transactions : an International Journal of Inorganic Chemistry·Daisuke Takeuchi
Nov 10, 2005·Chemical Reviews·John R SevernNic Friederichs
May 23, 2013·Journal of the American Chemical Society·Kaitlyn E Crawford, Lawrence R Sita
Jan 25, 2013·Journal of the American Chemical Society·Jia WeiLawrence R Sita

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