Mechanistic Study of Bu2SnCl2‐Mediated Ring‐Opening Polymerization of ε‐Caprolactone by Multinuclear NMR Spectroscopy

Publisher Website
Google Scholar
Abstract
The ring‐opening polymerization (ROP) of ε‐caprolactone (CL) was carried out in toluene at 100 °C with n‐propanol (nPrOH) in the presence of Bu2SnCl2. It comes out that the molar mass of the polyester chains can be predicted from the initial monomer‐to‐alcohol molar ratio in accordance with a controlled ROP mechanism involving an O‐acyl cleavage of the monomer to selectively form (α‐propyloxy)(ω‐hydroxy)poly(ε‐caprolactone) chains. In order to gain fundamental understanding of the mechanistic factors governing the polyester chain growth, advanced 1H, 13C, and 119Sn NMR investigations were performed in situ in [D8]toluene, as well as with model solutions that contained Bu2SnCl2 and binary mixtures of the components at various concentrations and temperatures. This has enabled us to propose a mechanism in which Bu2SnCl2 behaves as a catalyst, while nPrOH is the actual initiator. It involves non‐aggregated, six‐coordinate Bu2SnCl2 complexes in which ligands exchange fast on the 119Sn NMR observational timescale, and the simultaneous interactions of CL and alcohol function in such a way that it favors insertion/propagation reactions over transesterification ones, up to high monomer conversion.

This publication has 27 references indexed in Scilit: