Precise Carboxylic Acid-Functionalized Polyesters in Reprocessable Vitrimers

Thermosets are valued for their exceptional dimensional stability, mechanical properties, and resistance to creep and chemicals. Their permanent molecular structures limit reshaping, reprocessing, and recycling. Incorporating exchangeable chemical bonds into cross-linked polymer networks provides materials with thermoset-like properties that are also reprocessable. Here, ring-opening copolymerization (ROCOP) of unpurified, commercially available epoxides and succinic anhydride is employed to synthesize well-defined, low molecular weight polyesters with controlled functionalization. Polymer networks are then formed through the catalyzed reaction of these copolymers with the epoxy-containing cross-linker diglycidyl ether of bisphenol A. Catalyst mixtures of zinc bis(2-ethylhexanoate) and 1,8-diazabicyclo(5.4.0)undec-7-ene are used to assess the role of the catalysts in the curing and dynamic bond exchange reactions. Varying the catalyst ratios results in polymer networks with tunable mechanical properties (90% < ε_b < 450%, 0.30 MPa < UTS < 24 MPa), high creep recovery (%recovery > 90% after five creep cycles), and good reprocessability.