Titanium Complexes of Dialkanolamine Ligands as Initiators for Living Ring-Opening Polymerization of ε-Caprolactone

The titanium complexes with one (1a, 1b, 1c) and two (2a, 2b) dialkanolamine ligands were used as initiators in the ring-opening polymerization (ROP) of epsilon-caprolactone. Titanocanes 1a and 1b initiated living ROP of epsilon-caprolactone affording polymers whose number-average molecular weights (M-n) increased in direct proportion to monomer conversion (M-n <= 30,000 g mol(-1)) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (M-w/M-n <= 1.2 up to 80% monomer conversion). H-1-NMR and MALDI-TOF-MS studies of the obtained poly(epsilon-caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti-(OPr)-Pr-i bond of the catalyst. The higher molecular weight polymers (M-n <= 70,000 g mol(-1)) with reasonable MWD (M-w/M-n < 1.6) were synthesized by living ROP of epsilon-caprolactone using spirobititanocanes (2a, 2b) and titanocane 1c as initiators. The latter catalysts, according MALDI-TOF-MS data, afford poly(epsilon-caprolactone)s with almost equal content of alpha,omega-dihydroxyl- and alpha-hydroxyl-omega(carboxylic acid)-terminated chains arising due to monomer insertion into "Ti-O" bond of dialkanolamine ligand and from initiation via traces of water, respectively. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230-1240, 2010