Tunable Biobased Epoxy Networks via Zn(acac)₂: From Limited Esterification to Dynamic Structures

Abstract In this work, the influence of zinc acetylacetonate (Zn(acac) 2 ) as a catalyst on the curing/crosslinking, thermal stability, degradation, and rheological properties of epoxidized soybean oil (ESO) and sebacic acid (SA) systems is elucidated. Formulations containing 0, 2.5 and 10 wt% Zn(acac) 2 were characterized by FTIR, DSC, TG–IR, rheology and swelling/gel fraction analyses. FTIR confirmed extensive epoxy consumption (> 97%), while DSC revealed that increasing Zn(acac) 2 content systematically lowered the curing temperature and reorganized the reaction pathway, resulting in a reduced apparent reaction enthalpy, which reflects the involvement of Zn 2+ in the esterification process and more efficient network formation. TG–IR analysis demonstrated that, although Zn(acac) 2 decreases the onset of mass loss (T 5% ), it significantly increases the temperature required for 95% mass loss (T 95% ) and the residual mass, evidencing a transition to a more densely crosslinked structure promoted by increasing catalyst content. Rheology showed higher storage modulus, slower stress relaxation and elevated activation energies for topological rearrangement at higher catalyst concentrations, indicating the formation of coordination-restricted dynamic networks. Swelling and gel fraction measurements confirmed this enhanced architecture, showing reduced solvent uptake and increased insoluble content with increasing Zn(acac) 2 . Overall, Zn(acac) 2 acts simultaneously as a catalytic accelerator and as a structural coordinator, enabling control over curing kinetics, network topology and thermal stability, and establishing ESO–SA/Zn(acac) 2 as a tunable platform to design fully biobased polymer systems.