Titanium complexes of dialkanolamine ligands as initiators for living ring‐opening polymerization of ε‐caprolactone

Abstract

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 e-caprolactone. Titanocanes 1a and 1b initiated living ROP of e-caprolactone affording polymers whose number-average molecular weights (M n ) increased in direct proportion to monomer conversion (M n 30,000 g mol À1 ) 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). 1 H-NMR and MALDI-TOF-MS studies of the obtained poly(e-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-O i Pr bond of the catalyst. The higher molecular weight polymers (M n 70,000 g mol À1 ) with reasonable MWD (M w /M n 1.6) were synthesized by living ROP of e-caprolactone using spirobititanocanes (2a, 2b) and titanocane 1c as initiators. The latter catalysts, according MALDI-TOF-MS data, afford poly(e-caprolactone)s with almost equal content of a,x-dihydroxyl-and ahydroxyl-x(carboxylic acid)-terminated chains arising due to monomer insertion into ''Ti-O'' bond of dialkanolamine ligand and from initiation via traces of water, respectively.

Titanium complexes based on aminodiol ligands for the ring‐opening polymerization of ε‐caprolactone, rac‐β‐butyrolactone, and trimethylene carbonate

“…Almost all complexes acted as fairly active initiators, conversions above 60% were reached within 10 min at 70 °C, but no significant activity increase was observed when polymerizations were conducted at 100 °C. Nonetheless, the activity of these complexes (62.51–160.18 g poly mmol cat −1 h −1 ) was superior to that of titanium complexes having tellurium‐bridged bis(phenolate) ligands17 and similar to that of dialkanolamine titanium complexes 12. Such high activities could be explained by the coordination of axial nitrogen atom from the ligand to the titanium metal center reducing the activation energy for the CL polymerization 12…”

“…Lee and coworkers11 also reported CL polymerization using titanium complexes based on ketoiminate ligands with poor catalytic activity and poor control over the polymerization. Recently, titanium complexes of dialkanolamine ligands have been reported as efficient initiator for ROP of CL 12. Group(IV) metal complexes containing heteroatom‐bridged dialkoxide ligands {OZO} 2− (e.g., Z = N or S) are particularly attractive and reported as efficient initiator for ROP of other cyclic esters.…”

Heterodinuclear titanium/zinc catalysis: synthesis, characterization and activity for CO2/epoxide copolymerization and cyclic ester polymerization

“…S13 and Table S3 †) 25,27 but also showed a clear induction period of approximately 45 minutes, during which very low conversions were observed. Such induction or initiation periods are common for ε-CL polymerization with other Ti and group 4 iso-propoxide catalysts, 27,113,114 and are attributed to a structural rearrangement of the ligands of the initiator, allowing the monomer to access the metals coordination sphere prior to insertion. [115][116][117] Intriguingly, no such induction period is observed with L-LA, which may suggest that the two monomers differ in their coordination mode to the heterobimetallic catalyst systems.…”

Synthesis of poly(lactic acid) and the formation of poly(lactic acid)-based supraporous biofunctional materials for tissue engineering

“…The for mation of a low molecular mass fraction is associated with the appearance of macrocyclic structures via the side reaction of intramolecular transesterification. In [38], similar structures were detected via MALDI TOF MS. Separation of the low molecular mass fraction is of extreme importance during the formation of porous matrixes based on the high molecular mass polymer.…”