Frontally polymerizable shape memory polymer for 3D printing of free-standing structures

Abstract

Four-dimensional (4D) printing is used to describe three-dimensional (3D)-printed objects with properties that change over time. Shape memory polymers (SMPs) are representative materials for 4D printing technologies. The ability to print geometrically complex, free-standing forms with SMPs is crucial for successful 4D printing. In this study, an SMP capable of frontal polymerization featuring exothermic self-propagation was synthesized by adding cyclooctene to a poly(dicyclopentadiene) network, resulting in switching segments. The rheological properties of this SMP were controlled by adjusting incubation time. A nozzle system was designed such that the SMP could be printed with simultaneous polymerization to yield a free-standing structure. The printing speed was set to 3 cm/min according to the frontal polymerization speed. A free-standing, hexagonal spiral was successfully printed and printed spiral structure showed excellent shape memory performance with a fixity ratio of about 98% and a recovery ratio of 100%, thereby demonstrating the 3D printability and shape memory performance of frontally polymerizable SMPs.

Frontal Polymerizations: From Chemical Perspectives to Macroscopic Properties and Applications

“…Future efforts to achieve large-scale FP extrusion, however, may benefit from earlier works described in this review. 32,155,160,238,364 6. Summary and Outlook 6.1 Summary: Where are We Now?…”

“…Apart from ATRP and polyurethanes, which have not been thoroughly investigated, only FROMP occurs catalytically with the use of the commercial Grubbs-type ruthenium alkylidene complexes (e.g., G1 and G2). 32,41,49,66,69,70,73,102,106,124,[145][146][147]151,152,160,162,163 Highly strained, cyclic olefins undergo living catalytic polymerization; frontally derived polymers of dicyclopentadiene (DCPD) exhibit desirable mechanical properties via extensive crosslinking during catalysis. Perhaps counterintuitively to most catalyst design principles, FROMP and polyurethane-based systems 68,72,[193][194][195] require worse catalysts to circumvent rapid background polymerization.…”

“…The material properties are comparable with other bio-derived epoxy composites, but cure substantially faster than traditional thermal curing (i.e., 1 min vs. 24 h). 190 More recently, An and coworkers 160 employed FROMP to 3Dprint shape memory polymers in resins containing cyclooctene as a comonomer. Similar work from Appelhans and coworkers 363 demonstrated that stereolithographic additive manufacturing via photoROMP of DCPD can generate complex shapes with sub mmscale resolution (e.g., chess pieces).…”

“…Fabrication of free-standing objects via 3D printing or extrusion necessitates appropriately modified resin rheologies. 155,160,161,164,364 Specifically, printing inks must exhibit shape retention after pressurized extrusion (i.e., low mechanical flow). The following materials properties address the aforementioned printing criterion; resins must exhibit shear yielding, shear thinning, and fast thixotropic recovery behavior.…”

Multiple/Two‐Way Shape Memory Poly(urethane‐urea‐amide) Elastomers

“…Lendlein and Langer reported that SMPs may be used as self-tightening sutures for minimum invasive surgery in 2002, raising much interest for SMPs in biomedical applications. [15] Recent expansion from the traditional dual to multiple shape memory effect (M-SME) [16,17] and reversible two-way shape memory effects (2W-SMPs) [18][19][20] has greatly broadened the applications of SMPs, such as biomedical sciences, [21,22] temperature sensors, [9] actuators, [6] 3D printing, [1,23,24] flexible electronics, [11] smart textiles, [25,26] surgical materials, and aerospace devices. [27] Based on the number of fixed temporary shapes, SMPs can be divided into dual, triple, and multiple shape memory polymers.…”