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Mechanistic Study of Bu 2 SnCl 2 ‐Mediated Ring‐Opening Polymerization of ε‐Caprolactone by Multinuclear NMR Spectroscopy
Author(s) -
Deshayes Gaëlle,
Mercier Frédéric A. G.,
Degée Philippe,
Verbruggen Ingrid,
Biesemans Monique,
Willem Rudolph,
Dubois Philippe
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200304769
Subject(s) - monomer , chemistry , polymerization , polymer chemistry , ring opening polymerization , toluene , molar mass , polyester , nuclear magnetic resonance spectroscopy , transesterification , caprolactone , copolymer , catalysis , polymer , stereochemistry , organic chemistry
The ring‐opening polymerization (ROP) of ε‐caprolactone (CL) was carried out in toluene at 100 °C with n ‐propanol ( n PrOH) in the presence of Bu 2 SnCl 2 . 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 1 H, 13 C, and 119 Sn NMR investigations were performed in situ in [D 8 ]toluene, as well as with model solutions that contained Bu 2 SnCl 2 and binary mixtures of the components at various concentrations and temperatures. This has enabled us to propose a mechanism in which Bu 2 SnCl 2 behaves as a catalyst, while n PrOH is the actual initiator. It involves non‐aggregated, six‐coordinate Bu 2 SnCl 2 complexes in which ligands exchange fast on the 119 Sn 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.