A Highly Efficient Initiator for the Ring-Opening Polymerization of Lactides and ε-Caprolactone:  A Kinetic Study

A trinuclear zinc alkoxide [{(BDI-OMe)Zn(μ-OBn)} 2 Zn(μ-OBn) 2 ] ( 1 ) and a homoleptic zinc complex [(BDI-OMe) 2 Zn] ( 2 ) have been prepared by the addition of benzyl alcohol to a mixture of BDI-OMe-H with Et 2 Zn. Compound 1 has been employed as an initiator for ring-opening polymerization of lactides and ε-caprolactone. The highly efficient initiator of the zinc complex shown in the polymerization process enabled us to synthesize the PLA at ambient temperature, yielding PLA with well molecular control and narrow molecular weight distribution in a very short period of time. The polymerization kinetics were studied with [LA] 0 /[ 1 ] = 200/1 and [LA] 0 = 0.5 M at 25 °C. Experimental results indicate a second-order dependency on [LA] ( k obs = 0.033 M -1 s -1 ). Moreover, a first-order dependency in [ 1 ] is indicated of k obs vs [Initiator], with a slope equal to the first-order rate constant k = 12.2 M -2 s -1 . Furthermore, the heterotactic PLA with Pr up to 83% can be achieved in a mixed solvent of CH 2 Cl 2 and THF at −35 °C. However, according to polymerization kinetic studies of CL, a first-order dependency on [CL] and [ 1 ] is observed for ROP of ε-caprolactone.