Ring-Opening Polymerization of ε-Caprolactone by Phosphorane Iminato and Cyclopentadienyl Complexes of Rare Earth Elements

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Ravi, Palaniswamy ; Gröb, Thorsten ; Dehnicke, Kurt ; Greiner, Andreas:
Ring-Opening Polymerization of ε-Caprolactone by Phosphorane Iminato and Cyclopentadienyl Complexes of Rare Earth Elements.
In: Macromolecular Chemistry and Physics. Bd. 202 (2001) Heft 12 . - S. 2641-2647.
ISSN 1521-3935
DOI: https://doi.org/10.1002/1521-3935(20010801)202:12<2641::AID-MACP2641>3.0.CO;2-Q

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Abstract

Rare earth element complexes with triphenyl phosphorane iminato ligands such as [La2(NPPh3)4(μ-NPPh3)2(μ-THF)] and [Yb(NPPh3)3]2 initiate the polymerization of ε-caprolactone to give high molecular weight poly(ε-caprolactone) with moderate polydispersity. The reactivity of these complexes is higher as compared to complexes with three cyclopentadienyl ligands with corresponding metal centers. The initiation mechanism for the polymerization of ε-caprolactone by [La2(NPPh3)4(μ-NPPh3)2(μ-THF)] is discussed based on the end groups of low molecular weight polycaprolactones. Living chain ends of poly(ε-caprolactone) were proved by block copolymerization of ε-caprolactone and δ-valerolactone. The mixed complex [Cp3Dy2(NPPh3)3] has been successfully applied for ROP of CL. A significant increase in molecular weight of ROP has been observed with decrease of reaction temperature.