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

Abstract

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 (PPh 3 ) 3 ( I ), TpRuCl(PPh 3 ) 2 ( II ), and TpRuCl(PHPh 2 )(PPh 3 ) ( 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. 1 H and 13 C 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 1 H, 13 C, and 31 P NMR, gel permeation chromatography (GPC), and MALDI‐TOF analysis of the polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6926–6942, 2006