Immortal ring-opening polymerization of lactides with super high monomer to catalyst ratios initiated by zirconium and titanium complexes containing multidentate amino-bis(phenolate) ligands

Zirconium complexes (L2Zr, L = -OC6H2-4-R-1-6-R-2-2-CH2-N[(CH2)(3)-N(CH2CH2)(2)O]-CH2-4-R-1-6-R-2-C6H2O-, R-1 = Me, R-2 = Bu-t, complex 1; R-1 = R-2 = Bu-t, complex 2) containing two symmetrical amino-bis(phenolate) ligands were prepared. Moreover, titanium complexes (LTi((OPr)-Pr-i)(2), L = -OC6H2-4-R-1-6-R-2-2-CH2-N[(CH2)(3)-N( CH2CH2)(2)O]-CH2-4-R-1-6-R-2-C6H2O-, R-1 = Me, R-2 = Bu-t, complex 3; R-1 = R-2 = tBu, complex 4) based on symmetrical amino-bis(phenolate) ligands were synthesized. These complexes were characterized by H-1 and C-13 NMR spectroscopy and elemental analyses. The solid-state structures of complexes 2 and 3 were determined by X-ray diffraction. Complexes 1, 2, 3, and 4 were highly active initiators for the ring-opening polymerization of L-lactide (L-LA) and rac-lactide (rac-LA). The experimental results show that complexes 1 and 2 are highly active and excellent catalysts for the immortal ring-opening polymerization (iROP) of L-lactide and rac-lactide in the melt state. The monomer-to-complex ratio reached 200000/1, which is the highest feeding molar ratio of lactide so far, to the best of our knowledge. Meanwhile, a narrow poly-dispersity index (1.11-1.58) of polymers was obtained, and the number-average molecular weight approached 8.64 x 10(4) g mol(-1). The turnover frequency (TOF) reached 6593 h(-1), and the polymerization proceeded smoothly even in an air environment.