Di-, Tri- and Tetrafunctional Poly(ε-caprolactone)s by Bi(OAc)3-Catalyzed Ring-Opening Polymerizations of ε-Caprolactone

ε-Caprolactone was polymerized in bulk at 150 °C with either tetra(ethylene glycol) (TEG), 1,1,1-tris(hydroxymethyl)propane, or Pentaerythritol as initiator and bismuth(III) acetate Bi(OAc)3 as catalyst. The reaction times needed for nearly quantitative conversion were determined. The polylactones isolated after precipitation were characterized by 1H NMR spectroscopy and MALDI−TOF mass spectroscopy. Quantitative incorporation of the initiators were confirmed, so that polylactones having two, three, or four OH end groups were obtained. A coordination−insertion mechanism explaining these results is discussed. When used as catalyst for ring-opening polymerizations of lactones and lactides bismuth(III) carboxylates have three important advantages, particularly low toxicity, low transesterification activity (“backbiting degradation”), and no racemization when l-lactide is polymerized at temperatures up to 180 °C.