Initiation of vinylphosphonate group transfer polymerization with unbridged rare earth metallocenes (Cp2LnX) follows a complex reaction pathway. Depending on the nature of X, initiation can either proceed via deprotonation of the acidic a-CH of the vinylphosphonate (e.g. X = Me, NR2), via nucleophilic transfer of X to a coordinated monomer (e.g. X = Cp, SR) or via a monomer- (i.e. donor) induced ligand exchange reaction forming Cp3Ln in equilibrium (e.g. X = Cl, OR), which serves as the active initiating and catalytic species. As observed by ESI-MS end group analysis, different initiations may also occur simultaneously. These findings were confirmed by NMR spectroscopic measurements of phosphonate coordination at the corresponding Lu and Y centers, and are further supported by kinetic investigations as well as by X-ra ycrystallography. Kinetic 31P NMR spectroscopic studies revealed the rate determining step of chain growth and that propagation proceeds in a monometallic fashion.

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

243rd National Meeting (2012)

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