4D Printing of Triple-Shape Memory Cyanate Composites Based on Interpenetrating Polymer Network Structures

The triple-shape memory polymer (TSMP) can be programmed into two temporary shapes (S₁ and S₂) and shows an ordinal recovery from S₂ to S₁ and eventually to the permanent shape upon heating, which realizes more complex stimulus-response motions. We introduced a novel strategy for forming triple-shape memory cyanate ester (TSMCE) resins with high strength and fracture toughness via three-step curing, including four-dimensional (4D) printing, UV post-curing, and thermal curing. The obtained TSMCE resins presented two separated glass transition temperature (T_g) regions due to the formation of an interpenetrating polymer network (IPN), which successfully endowed the polymers with the triple-shape memory effect. The two T_g increased with the increasing cyanate ester (CE) prepolymer content; their ranges were 82.7-102.1 °C and 164.4-229.0 °C, respectively. The fracture strain of the IPN CE resin was up to 10.9%. Moreover, the cooperation of short carbon fibers (CFs) and glass fibers (GFs) with the polymer-accelerated phase separation resulted in two well-separated T_g peaks exhibiting better excellent triple-shape memory behaviors and fracture toughness. The strategy for combining the IPN structure and 4D printing provides insight into the preparation of shape memory polymers integrating high strength and toughness, multiple-shape memory effect, and multifunctionality.