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.

Shape Memory Epoxy Resin and Its Composites: From Materials to Applications

Shape memory polymers (SMPs) have historically attracted attention for their unique stimulation-responsive and variable stiffness and have made notable progress in aerospace, civil industry, and other fields. In particular, epoxy resin (EP) has great potential due to its excellent mechanical properties, fatigue resistance, and radiation resistance. Herein, we focus on the molecular design and network construction of shape memory epoxy resins (SMEPs) to provide opportunities for performance and functional regulation. Multifunctional and high-performance SMEPs are introduced in detail, including multiple SMEPs, two-way SMEPs, outstanding toughness, and temperature resistance. Finally, emerging applications of SMEPs and their composites in aerospace, four-dimensional printing, and self-healing are demonstrated. Based on this, we point out the challenges ahead and how SMEPs can integrate performance and versatility to meet the needs of technological development.

Improved thermal and mechanical properties of bismaleimide nanocomposites via incorporation of a new allylated siloxane graphene oxide

A thermosetting resin system based on bismaleimide (BMI) has been developed via copolymerization with 4,4′-diaminodiphenylsulfone in the presence of a newly synthesized graphene oxide, modified using allylated siloxane (AS-GO). The curing behavior of the AS-GO-containing resin system was evaluated using curing kinetics. The dispersibility of AS-GO in the resin was observed through polarizing optical microscopy (POM), which indicates that AS-GO has good dispersibility in the resin due to GO modified with allylated siloxane which has a good phase compatibility with BMI. The effect of AS-GO on the thermomechanical and mechanical properties of the cured modified resin was also studied. Results of thermogravimetric analysis indicated that the cured sample systems display a high char yield at lower concentrations of AS-GO (≤0.5 wt%) with an improved thermal stability. Using dynamic mechanical analysis, a marked increase in glass transition temperature (T_g) with increasing AS-GO content was observed. Mechanical property analyses revealed a possible effect of AS-GO as a toughener, and the results showed that an addition of 0.3% AS-GO maximized the toughness of the modified resin systems, which was confirmed by analysis of fracture surfaces.

A thermosetting resin system based on bismaleimide has been developed via copolymerization of a new allylated siloxane graphene oxide.

Enhanced tribological properties of bismaleimides with a novel hybrid silicon dioxide containing amino groups

To improve the tribological properties of bismaleimide (BMI) resin, silicon dioxide nanoparticles with imino and terminal functional amino groups were prepared through a sol–gel process to form a novel SiO2-NH2 hybrid. The as-prepared hybrid was then applied as a modifying agent for the BMI matrix to obtain SiO2-NH2/BMI composites. Compared to those of pure BMI resin, the volume wear rate and friction coefficient of the SiO2-NH2/BMI composites decreased significantly, while the wear mechanism changed from fatigue (BMI) to adhesive (SiO2-NH2/BMI) wear. This improvement in the tribological properties of the SiO2-NH2/BMI composites was attributed to the appropriate SiO2-NH2 added content, which endowed the BMI with excellent mechanical and thermal-resistant properties. Thus, the SiO2-NH2/BMI composites could resist the external load and excessive heat during the friction process.

Two-Way and Multiple-Way Shape Memory Polymers for Soft Robotics: An Overview

Shape memory polymers (SMPs) are smart materials capable of changing their shapes in a predefined manner under a proper applied stimulus and have gained considerable interest in several application fields. Particularly, two-way and multiple-way SMPs offer unique opportunities to realize untethered soft robots with programmable morphology and/or properties, repeatable actuation, and advanced multi-functionalities. This review presents the recent progress of soft robots based on two-way and multiple-way thermo-responsive SMPs. All the building blocks important for the design of such robots, i.e., the base materials, manufacturing processes, working mechanisms, and modeling and simulation tools, are covered. Moreover, examples of real-world applications of soft robots and related actuators, challenges, and future directions are discussed.

Structural design of polyurethane/poly(butylene succinate)/polycaprolactone compounds via a multilayer-assembled strategy: achieving tunable triple-shape memory performances

Novel strategy for structural design of multicomponent systems via layer-multiplying co-extrusion: achieving tunable triple-shape memory performances of polyurethane/poly(butylene succinate)/polycaprolactone compounds.