Poly(ethylene imine)-Based Covalent Adaptable Networks: Influence of the Dialdehyde Structure on Thermoset Properties

Abstract

With the aim of developing circular thermosets, with CO2 absorption properties, branched polyethylenimine based covalent adaptable networks were synthesized using cross-linker agents derived from hydroxybenzaldehyde, a wood derivative, and deeply characterized. The incorporation of dynamic imine bonds within the network led to thermoreversible materials capable of rearranging upon heating. Network relaxation was studied and activation energy (Ea) determined following Kohlrausch–Williams–Watt (KWW) model. Ea ranging from 20 to 75 kJ/mol were determined according to the thermoset structure. Reprocessability of the materials by thermal compression molding over 120 °C was achieved and complete recovery of the mechanical properties was still evidenced after three reprocessing cycles indicating a possible circularity of these thermosets. When the cross-linking agent did not contain any poly(ethylene glycol) (PEG) moiety, networks ranging from gums to rigid materials were obtained with glass transition temperatures (Tg) ranging from −40 to 39 °C depending on the cross-linker concentration. Swelling rate ranged from 368% to 42% and extraction rate from 21% to 5%. When the cross-linking agent contained a PEG block, softer materials were obtained with Tg ranging from −6 to 22 °C, swelling rates ranging from 515% to 84% and extraction rate from 68% to 1%. CO2 absorption, studied using thermogravimetric analysis, was more pronounced for these last PEG-containing materials confirming PEG affinity for this polar gas.