Mechanistic studies on initiation and propagation of rare earth metal-mediated group transfer polymerization of vinylphosphonates

Stephan Salzinger, Benedikt S. Soller, Andriy Plikhta, Uwe B. Seemann, Eberhardt Herdtweck, Bernhard Rieger

Publikation: Beitrag in FachzeitschriftArtikelBegutachtung

48 Zitate (Scopus)

Abstract

Initiation of rare earth metal-mediated vinylphosphonate polymerization with unbridged rare earth metallocenes (Cp2LnX) follows a complex reaction pathway. Depending on the nature of X, initiation can proceed either via abstraction of the acidic α-CH of the vinylphosphonate (e.g., for X = Me, CH2TMS), via nucleophilic transfer of X to a coordinated monomer (e.g., for X = Cp, SR) or via a monomer (i.e., donor)-induced ligand-exchange reaction forming Cp3Ln in equilibrium (e.g., for X = Cl, OR), which serves as the active initiating species. As determined by mass spectrometric end group analysis, different initiations may also occur simultaneously (e.g., for X = N(SiMe2H)2). A general differential approach for the kinetic analysis of living polymerizations with fast propagation and comparatively slow initiation is presented. Time-resolved analysis of monomer conversion and molecular weights of the formed polymers allow the determination of the initiator efficiency throughout the whole reaction. Using this normalization method, rare earth metal-mediated vinylphosphonate GTP is shown to follow a Yasuda-type monometallic propagation mechanism, with an S N2-type associative displacement of the polymer phosphonate ester by a monomer as the rate-determining step. The propagation rate of vinylphosphonate GTP is mainly determined by the activation entropy, i.e. the change of rotational and vibrational restrictions within the eight-membered metallacycle in the rate-determining step as a function of the steric demand of the metallacycle side chains and the steric crowding at the metal center.

OriginalspracheEnglisch
Seiten (von - bis)13030-13040
Seitenumfang11
FachzeitschriftJournal of the American Chemical Society
Jahrgang135
Ausgabenummer35
DOIs
PublikationsstatusVeröffentlicht - 4 Sept. 2013

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