Radical Oxidation of Itaconic Acid-Derived Unsaturated Polyesters under Thermal Curing Conditions

Itaconic acid has attracted a lot of interest as a green and low-cost building block toward the synthesis of biobased polyesters and polyurethanes with a wide range of applications in the UV-curing field. However, the thermal curing of itaconic acid-derived polyesters has been not extensively investigated. To gain deeper insight into the thermally induced crosslinking process, the curing of poly(hexylene itaconate) was investigated by advanced isoconversional analysis performed under isothermal and non-isothermal conditions. Rheology and thermal analysis pointed out a three-step mechanism (initiation, propagation, and termination) typical of free-radical polymerization associated with the double bond conversion. Moreover, due to the comprehensive information obtained by different analytical techniques such as isothermal DSC, ATR-FTIR, and DMTA, we speculate that thermo-oxidative mechanisms occur under thermal curing conditions of poly(hexylene itaconate). Thus, β-scissions of poly(hexylene itaconate) chains might lead to the formation of anhydride and oligomeric radicals, which can recombine to a highly branched and crosslinked poly(hexylene itaconate) resin.