Monoaryloxo ytterbium(III) chlorides supported by β-diketiminato ligands as novel initiators for the living ring-opening polymerization of ε-caprolactone

Abstract

Ring-opening polymerization of ε-caprolactone (ε-CL) was carried out using β-diketiminato-supported monoaryloxo ytterbium chlorides L 1Yb(OAr)Cl(THF) (1) [L1 = N,N'-bis(2,6-dimethylphenyl)-2, 4-pentanediiminato, OAr = 2,6-di-tert-butylphenoxo-], and L2Yb(OAr') Cl(THF) (2) [L2 = N,N'-bis(2,6-diisopropylphenyl)-2,4- pentanediiminato, OAr' = 2,6-di-tert-butyl-4-methylphenoxo-], respectively, as single-component initiator. The influence of reaction conditions, such as polymerization temperature, polymerization time, initiator, and initiator concentration, on the monomer conversion, molecular weight, and molecular weight distribution of the resulting polymers was investigated. Complex 1 was well characterized and its crystal structure was determined. Some features and kinetic behaviors of the CL polymerization initiated by these two complexes were studied. The polymerization rate is first order with respect to monomer. The Mn of the polymer increases linearly with the increase of the polymer yield, while polydispersity remained narrow and unchanged throughout the polymerization in a broad range of temperatures from 0 to 50°C. The results indicated that the present system has a "living character". © 2005 Wiley Periodicals, Inc.