Synthesis of Poly(ε-caprolactone) Carried Out with Zirconium Acetylacetonate: Polymerization Kinetics and Molecular Weight of the Polymers

Kinetics of polymerization of ε-caprolactone initiated by zirconium acetylacetonate Zr(acac)4 in the presence of ethylene glycol as a co-initiator was studied. Detailed kinetic analysis was performed using Friedman differential isoconversional method in combination with analysis of the enthalpy–entropy compensation effect, resulting in model-free evaluation of the kinetic triplet of the reaction: $${{E}_{{{\alpha }}}}$$ , $${{A}_{{{\alpha }}}}$$ , and $$f\left( {{\alpha }} \right)$$ . In addition, the activation energy $${{E}_{{{\alpha }}}}$$ was calculated using the first-order reaction model. The obtained value $${{E}_{{{\alpha }}}}$$ = 65.5 ± 2.3 kJ/mol was consistent with the average $${{E}_{{{\alpha }}}}$$ values calculated by the isoconversional method. It was shown that the sigmoidal nature of polymerization is adequately described by the Kamal autocatalytic model. The effect of reaction temperature and initiator concentration on the molecular-weight characteristics of resulting poly(ε-caprolactone) was investigated. When the reaction temperature is 100–140°C, the molecular weight of the polymer is Mn ≈ 40–50 kDa and the dispersity is Ð ≈ 1.7–2.0.