Several titanium complexes based on aminodiol ligands were tested as initiators for the ring-opening polymerization (ROP) of epsilon-caprolactone under solution and bulk conditions. All complexes were found to be efficient under both conditions. For bulk polymerization at 70 degrees C, high activities were observed (113.3-156.2 g(poly) mmol(cat)(-1) h(-1)) together with controlled molar mass distribution. Kinetic studies revealed controlled polymerization, and the chain propagation was first order with respect to monomer conversion. One complex was also tested for the ROP of rac-beta-butyrolactone and the end-group analysis suggested that ring opening occurs through acyl-oxygen bond cleavage via coordination-insertion mechanism. The microstructure analysis of polymer by (13)C NMR indicates atactic polymer. Another complex was also found to be efficient initiator for the ROP of trimethylene carbonate under solution and bulk conditions. Again, end-group analysis suggests coordination- insertion mechanism. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 5176-5185, 2011