Acidic bismuth salts, such as BiCl3, BiBr3, BiJ(3), and Bi-triflate catalyzed the ring-opening polymerization of 2-methoxazoline (MOZ) in bulk at 100 degrees C, whereas less acidic salts such as Bi2O3 or Bi(III)acetate did not. Bi-triflate-catalyzed polymerizations of 2-ethyloxazoline (EtOZ) were performed with variation of the monomer-catalyst ratio (MIC). It was found that the molecular weights were independent of the MIC ratio. The formation of cationic chain ends and the absence of cycles was proven by reactions of virgin polymerization products with NN-dimethyl-4-aminopyridine or triphenylphosphine. The resulting polymers having modified cationic chain ends were characterized by H-1 NMR spectroscopy and MALDI-TOF mass spectrometry. The polymerization mechanism including chain-transfer reactions is discussed. (C) 2008 Wiley Periodicals, Inc.