In contrast to BiF3, the other three Bi-halides catalyzed the ring-opening polymerization of epsilon-caprolactone (epsilon-CL) in bulk. A temperature of 140 degrees C was found to be advantageous for rapid polymerization and optimum molecular weights. At this temperature, the reactivity of the catalysts increases in the order BiCl3 < BiBr3 < BiJ(3). Variation of the monomer-catalyst ratio (M/C) yielded number-average molecular weights (M(n)s) up to 80,000 Da (corrected SEC data, 120,000 Da uncorrected), but a proper control of the M(n)s was not achieved. In addition to CH2-OH endgroups, CH2Cl, CH2Br, and CH(2)J endgroups were detected, but no evidence for a cationic polymerization mechanism was found. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7483-7490, 2008