Ring-opening polymerization of epsilon-caprolactone and delta-valerolactone using new Sm(III) mu-Halo-bis(trimethylsilyl)amido complexes

New Sm(III) mu-halo-bis(trimethylsilyl)amido complexes [Sm(mu-X) {N(SiMe3)( 2)}(2)(THF)](2) (X = Cl, Br) were synthesized and their crystal structures were analyzed. These complexes were used as catalysts for the homopolymeriz ation of epsilon-caprolactone and delta-valerolactone and found to initiate ring-opening polymerization (ROP) of these monomers in high conversion ove r a short period, giving homopolymers with a moderate polydispersity index (similar to 2.0). The effect of temperature and the catalyst amount on the molecular weight distribution was also studied. Mechanistic studies were co nducted using 1 : 1 and 1 : 6 molar ratios of mu-halo-bis-(trimethylsilyl)a mido complexes and epsilon-caprolactone by H-1-NMR and C-13-NMR spectroscop ic techniques and revealed the presence of more than one initiating species . (C) 1999 John Wiley & Sons, Inc.