Ring opening polymerization of ε-caprolactone initiated by titanium and vanadium complexes of ONO-type schiff base ligand

Abstract

A phenoxy-imine proligand with the additional OH donor group, 4,6-tBu2-2-(2-CH2(OH)-C6H4N = CH)C6H3OH (LH2), was synthesized and used to prepare group 4 and 5 complexes by reacting with Ti(OiPr)4 (LTi) and VO(OiPr)3 (LV). All new compounds were characterized by the FTIR, 1H and 13C NMR spectroscopy and LTi by the single-crystal X-ray diffraction analysis. The complexes were used as catalysts in the ring opening polymerization of ε-caprolactone. The influence of monomer/transition metal molar ratio, reaction time, polymerization temperature as well as complex type was investigated in detail. The complexes showed high (LTi) and moderate (LV) activity in ε-caprolactone polymerization and the resultant polycaprolactones exhibited Mn and Mw/Mn values ranging from 4.0 · 103 to 18.7 · 103 g/mol and from 1.4 to 2.5, respectively.

Coordination of ε-Caprolactone to a Cationic Niobium(V) Alkoxide Complex: Fundamental Insight into Ring-Opening Polymerization via Coordination–Insertion

“…In addition to a recent report from Plaman and Durr regarding the catalytic application of phenoxyimino Nb and Ta ethoxides, and Al-Khafaji and co-worker’s work encompassing the use of calixarene-supported NbCl 5 as a ROP initiator, reports from the groups of Chakraborty and Redshaw concerning, respectively, the use of Nb and Ta imino phenoxides and tetraphenolate-supported Nb and Ta species, , and a poorly controlled trihydridoniobocene system reported by Otero and co-workers, remain the only examples of these metals being successfully applied to the polymerization of ε-caprolactone. Several vanadium-catalyzed protocols have also been reported for the ROP of cyclic esters, including for ε-caprolactone. – …”

Titanium and Vanadium Complexes of Tridentate Phenoxy-Imine and Phenoxy-Amine Ligands and Their Application in the Ring-Opening Polymerization of Cyclic Esters

“…The synthesis and characterization of the phenoxy-imine proligand, L 1 H 2 , as well as the corresponding titanium ( Ti-L 1 ) and vanadium ( V-L 1 ) complexes, were reported in our previous communication [ 41 ]. In this work, we synthesized two novel [ONO]-type proligands and corresponding complexes.…”

“…Despite numerous reports that describe the behavior of titanium complexes in the ROP, there have been published only very few papers on vanadium complexes bearing ligands with O and N donor atoms, e.g., bi- and tridentate phenoxy-imine, tetradentate [ONNO]-type, and ligands derived from potentially tridentate 6-bis(o-hydroxyaryl)pyridines [ 41 , 42 , 43 ]. All of them were shown to promote the polymerization of ε -caprolactone but they turned out to be significantly less effective than titanium complexes with multidentate ligands.…”

Vanadium Complexes Derived from O,N,O-tridentate 6-bis(o-hydroxyalkyl/aryl)pyridines: Structural Studies and Use in the Ring-Opening Polymerization of ε-Caprolactone and Ethylene Polymerization

“…In particular, we and others have found that very high catalytic activities and thermally robust systems are accessible for α-olefin polymerization when conducted in the presence of co-catalysts such as dimethylaluminium chloride and the re-activator ethyl trichloroacetate [19][20][21][22][23][24][25][26][27][28][29][30][31], as well as ethylene copolymerization with the likes of propylene, 1-hexene or norbonene [32][33][34][35][36][37][38][39][40][41]. Moreover, a number of vanadyl-containing systems have shown promise in the ROP of cyclic esters [42,43], whilst other systems have been shown to be promising for both ROP and α-olefin polymerization [44][45][46][47][48][49]. We also note the favourable toxicity of vanadyl complexes; for example, vanadyl sulfate is not only used as a supplement but has shown promising behaviour against Type 2 diabetes [50].…”