Ring-opening polymerization of ɛ-caprolactone by lanthanide tris(2,4,6-tri-tert-butylphenolate)s: Characteristics, kinetics and mechanism

Lanthanide tris(2,4,6-tri-tert-butylphenolate)s are highly active initiators for ring-opening polymerization of ɛ-caprolactone to give polycaprolactone with number average molecular weight as high as 8.3 × 104 at 20 °C in 20 min in toluene. The effects of solvent, rare earth element, monomer/initiator molar ratio, monomer concentration, as well as polymerization temperature and time have been investigated. The kinetic studies of ɛ-caprolactone polymerization have indicated that the polymerization rate is first-order with respect to both monomer and initiator concentrations. The overall activation energy amounts to 39.3 kJ/mol. Mechanistic studies show that the monomer inserts into the growing chain with the acyl-oxygen bond scission.

The end group analyses on prepared polymer demonstrate that the ring-opening polymerization of ɛ-caprolactone with lanthanum tris(2,4,6-tri-tert-butylphenolate)s in toluene proceeds via a coordination–insertion mechanism. The monomer coordinated to rare earth metal, and opened its ring via acyl-oxygen bond cleavage forming a growing chain. The following monomer repeated these steps to insert into the Ln–O bond in the propagation process.Figure optionsDownload as PowerPoint slide