Diphenyl bismuth bromide (Ph2BiBr) allows for polymerizations of e-caprolactone in bulk at temperatures as low as 40 degrees C. Time conversion curves indicate a lower reactivity than tin(II) 2-ethyl hexanoate (SnOct(2)) Plus alcohol at 120 degrees C and also at 60 degrees C. Ph2BiBr also proved to be less reactive than Ph2BiOEt, but more reactive than BiBr3 and Bi(III)n-hexanoate. Small amounts (<= 1 wt %) of cyclic oligoester were detectable by MALDI-TOF mass spectrometry even at a polymerization temperature of 40 degrees C. The molar masses depend on the monomer-initiator ratio (M/I) but not in a simple parallel manner. With M/I = 600/1 number average molecular weights (M(n)s, corrected values) around 500 kDa were obtained. Even at low M/Is high molar mass polylactones were found and CH2Br endgroups were not detectable. However, upon addition of tetra(ethylene glycol) the coinitiator was completely incorporated yielding telechelic polylactones and the molar mass increased with the monomer-coinitiator ratio. (C) 2007 Wiley Periodicals, Inc.