High-temperature shape memory photopolymer with intrinsic flame retardancy and record-high recovery stress

Abstract Here we report an intrinsically flame-retardant high-temperature shape memory photopolymer (HTSMP) with ultrahigh glass transition temperature (Tg) of 280°C and record-breaking recovery stress of 35.3 MPa. Photopolymers have been widely used in 3D printing structures with high resolution by technologies such as digital light processing (DLP). However, a bottleneck persists in the lack of photopolymer inks integrated with high Tg, flame-retardancy, and high recovery stress, which are highly desired in several sectors such as in aerospace, automotive, construction, oil&gas, and electronic industries. In addition, photopolymers usually have low mechanical strength and toughness, limiting their use in critical load-bearing structures. In this study, a photopolymerizable isocyanurate triacrylate and a phosphine oxide photo-initiator were firstly formulated to prepare HTSMP through a facile two-step ultraviolet (UV) curing and thermal curing process. The UV curing makes the HTSMP 3D printable. After the unusual high-temperature (280 °C for 3 h) post-curing, the HTSMP network was highly crosslinked and uniform, which enhanced the strength and toughness. Additionally, the synergy between isocyanurate and phosphine oxide contributed excellent thermal stability and high flame-retardancy to the HTSPM, which cannot be ignited upon ten-second ignition for two times. A condensed-phase mechanism for flame-retardancy was also identified. With the ultrahigh Tg, record-high recovery stress and energy output, excellent thermal stability, intrinsic flame retardancy, and 3D printability, this new multifunctional HTSMP has a great potential in various applications, such as in deployable structures, damage self-healing, actuators, proppants, 4D printing, and robotics.