Di-, tri- and tetrafunctional poly(ε-caprolactone)s by Bi(OAc)3-catalyzed ring-opening polymerizations of ε-caprolactone

epsilon-Caprolactone was polymerized in bulk at 150 degreesC 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 H-1 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 180degreesC.