Abstract
Rare earth element complexes with triphenyl phosphorane iminato ligands such as [La 2 (NPPh 3 ) 4 (μ-NPPh 3 ) 2 (μ-THF)] and [Yb(NPPh 3 ) 3 ] 2 initiate the polymerization of e-caprolactone to give high molecular weight poly(e-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 e-caprolactone by [La 2 (NPPh 3 ) 4 (μ-NPPh 3 ) 2 (μ-THF)] is discussed based on the end groups of low molecular weight polycaprolactones. Living chain ends of poly(e-caprolactone) were proved by block copolymerization of e-caprolactone and δ-valerolactone. The mixed complex [Cp 3 Dy 2 (NPPh 3 ) 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.
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