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 1 H 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.