Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L‐lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L‐lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol(−1). Kinetic curves of D,L‐lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E(a)=44.51±5.35 kJ mol(−1), preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol(−1) K(−1). The effect of reaction conditions on the molecular weight of poly(D,L‐lactide) was shown.