Synthesis And Polvmerization Activities Of Rare Earth Amine-bis (Phenolate) Complexes

Lanthanide chloride complexes bearing amine-bis(phenolate) ligand Ln(ONN'O) (Ln= Nd, Sm, Gd and Lu) have been synthesized by metathesis reaction of anhydrous LnCl3 with amine-bis(phenolate) lithium salt in high yields. The complexes containing neodymium and samarium center were characterized, the single crystal X-ray crystallographic analysis shows these complexes are dimeric, consists of two seven-coordinate rare earth centers linked throughμ-Cl bridges. Neodymium chloride complex with tetradentate phenoxyamine (SALAN) ligand Nd(SALAN) was synthesized. Its single crystal X-ray crystallographic analysis shows this complex is also dimeric, consists of two six-coordinate neodymium centers linked throughμ-Cl bridges.The ring-opening polymerization (ROP) ofε-caprolactone (CL) was successfully carried out by using these lanthanide complexes as single component catalysts and the influence of the reaction conditions on the monomer conversion, molecular weight and molecular weight distribution of the resultant polymers was investigated. The neodymium complex (Nd(ONN'O))exhibits highest catalytic activities and leads to controlled ROP of CL, preparing PCLs with controlled molecular weights and narrow molecular weight distributions. Under the [Nd]/[CL] molar ratio of 200 or 300, polymerized in toluene at 80℃, the polymerization rate was first-order with respect to the monomer concentration. A long induction period was observed in this system, which attributes to the dissolution equilibrium of dimer-monomer of complex in solution.For the purpose of investigating the mechanism, a ROP of CL using Nd(ONN'O) with a 1:20 initiator to monomer molar ratio was carried out, and the polymerization was terminated by adding methanol. By controlling the transesterification reaction between aryl ester end group (ArOOC) and methanol, the oligomer ofε-caprolactone with or without phenol end group from ligand could be obtained. 1H NMR end group analyses and GPC determination demonstrate the coordination-insertion mechanism of ROP of CL catalyzed by amine-bis(phenolate) based rare-earth metal complexes directly.