High-Tg Vat Photopolymerization Materials Based on In Situ Sequential Interpenetrating Polymer Networks of Maleimide and Cyanate Ester Monomers

There are limited material choices for vat photopolymerization additive manufacturing processes that offer high dimensional accuracy. Acrylates and epoxies are commonly used, but their thermal properties are not suitable for applications requiring high-temperature performance. A possible solution is the use of high-performance thermosets, such as maleimide and cyanate ester, which are cured at high temperatures. Still, their use in vat photopolymerization methods has been limited due to the high temperature required. In this work, a photocurable formulation composed of multimaleimide monomers, a reactive diluent, and a cyanate ester was developed to improve thermal and mechanical properties and reduce cure shrinkage due to density changes during processing. In situ sequential interpenetrating polymer networks (IPNs) were investigated, in which the copolymerization of multimaleimide and a diluent occurs during printing, yielding a cyanate ester-swollen network with a sub-room-temperature glass transition temperature (<i>T_g</i>). The polymerization of the cyanate ester occurs during a high-temperature post-printing step. The resulting materials have a <i>T_g</i> above 250 °C (peak in the loss modulus), good fracture toughness (GIc of 100 J/m²), and overall cure shrinkage of less than 6%, with 1-2% occurring during the high-temperature post-curing step.