Structural and kinetic studies of the ring-opening polymerization of cyclic esters using N,N′ diarylformamidines Zn(II) complexes

The reactions of N,N′-bis(2,6-dimethylphenyl)formamidine (L1) and N,N′-bis(2,6-diisopropylphenyl)formamidine (L2), with Zn(OAc)2·2H2O salt and auxiliary benzoate ligands produced the respective Zn(II) formamidine benzoate complexes 1–4. All the complexes were characterized by IR, NMR spectroscopy elemental analysis and single crystal X-ray diffraction analyses for complexes 1, 2 and 3. Complexes 1–4 were active in the ring opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL), d,l-lactide (d,l-LA) and l-lactide (l-LA) monomers. The kinetic results indicated a pseudo-first order dependency on the monomers. The nature of the N,N′ diarylformamidines ligands, auxiliary benzoate and solvent were found to affect the catalytic activity as well as the properties of the polymers. Activation parameters obtained from Eyring plots for the ROP of ɛ-CL using complex 4 points to coordination insertion mechanism.

Graphical abstractDinuclear Zn(II) complexes with formamidine ligands and auxiliary benzoate ligands have been synthesized and studied by X-ray crystallography. The complexes were effective in the ring opening polymerization of cyclic esters to their respective polymers.Figure optionsDownload full-size imageDownload as PowerPoint slide