(338s) Gelation Behavior of Reversible Thermosets during Formation of Networks Depending on Design of Diels–Alder Precursors

Reversible thermosets using Diels–Alder (DA) chemistry can yield recyclable and self-healable 3D printing materials that form networks at low temperatures and depolymerize at high temperatures. For conventional thermosets, it is common to use multiple curing steps at elevated temperature to enhance their mechanical properties. Likewise, most reversible thermoset 3D printing materials need a post-curing step. However, a long post-curing step is a big challenge in 3D printing because it lengthens the overall process time, and the dimensions after the post-cure can vary from the original printing step. If the formation of the DA networks can be accelerated during a printing step, the post-cure step can be reduced or eliminated. In this presentation, gelation behavior was studied with various furan- and maleimide-functionalized precursors in terms of architecture, number of functionalities, and molecular weight. Synthesis of functional precursors were confirmed by FTIR and NMR. Thermomechanical properties of resultant polymers using various precursors were characterized through calorimetry and rheometry. Polymers from longer flexible precursors behaved more elastomeric with a lower glass transition temperature than those from short rigid precursors. The depolymerization of the network was confirmed by the endothermic reaction and moduli drop at ~120°C. The viscoelastic behavior over formation of networks was observed at 55°C and 80°C. The gelation time and time to reach a steady state modulus were determined and compared among various combinations of precursors. Both the gelation time and time to reach a steady state modulus decreased with more rigidity in the network. This result shows that design of precursors can affect gelation behavior during the formation of networks, and further studies can contribute to developing 3D printing reversible thermosets that do not need a post-curing step.