Ring opening polymerization of l-lactide with two different zinc(II) phenoxy-imine complexes as initiators

Abstract

This article reports the synthesis of two zinc(II) complexes containing phenoxy-imine ligands and their application as initiators of bulk ring opening polymerization (ROP) of L-lactide (LLA). The phenoxy-imine ligands (L1 and L2) were obtained by condensation reactions of salicylaldehyde derivatives with 2,6-diisopropylaniline. The reactions of L1 and L2 with ZnEt2 in the presence of n-BuOH afforded [Zn(L1)(OBu)] (C1) and [Zn(L2)(OBu)] (C2), which were characterized by elemental analysis, FTIR and 1H NMR spectroscopy. In addition, the geometries of both complexes were investigated by DFT (B3LYP/LACV3P∗∗) calculations. C1 and C2 were tested as initiators of ROP of LLA at 180 °C using different LLA/Zn molar ratios, namely 500, 1000 and 2500. Both complexes showed good activity, resulting in conversions up to 90-92% in 2 h. The poly(L-lactide) obtained displayed Mn ranging from 40.000-109.000, relatively low polydispersity (Mw/Mn = 1.2-2.1) and high stereoregularity with Tm = 176 °C.