Ring-opening polymerization of ε-caprolactone initiated with different ruthenium derivatives: Kinetics and mechanism studies

Abstract

End-functionalized polyesters have been synthesized by ring-opening polymerization (ROP) of ε-caprolactone (CL) initiated with five different ruthenium derivatives in the presence of a series of alcohols as transfer agents. Mechanistic studies were performed for ROP of CL with RuCl 2(PPh3)3 (I), TpRuCl(PPh3) 2 (II), and TpRuCl(PHPh2)(XPPh3) (III) as catalysts in the presence or absence of benzyl alcohol (BzOH). Obtained molecular weights are proportional to CL/BzOH ratio, but there is not a direct relationship with CL/ruthenium complex ratios. 1H and 13C NMR spectroscopy revealed the existence of benzyl ester end-groups. Catalysis involves (a) dissociation of ruthenium complexes, (b) coordination of the lactone CL, (c) coordination of the BzOH with the formation of a metal alkoxide, (d) transfer from the alkoxyl ligand to the coordinated lactone, and (e) ring-opening of CL by oxygen-acyl bond cleavage. The proposed mechanism is supported by 1H, 13C, and 31P NMR, gel permeation chromatography (GPC), and MALDI-TOF analysis of the polymers. © 2006 Wiley Periodicals, Inc.