Vitrimer-Like Shape Memory Polymers: Characterization and Applications in Reshaping and Manufacturing

Abstract

The shape memory effect (SME) refers to the ability of a material to recover its original shape, but only in the presence of a right stimulus. Most polymers, either thermo-plastic or thermoset, can have the SME, although the actual shape memory performance varies according to the exact material and how the material is processed. Vitrimer, which is between thermoset and thermo-plastic, is featured by the reversible cross-linking. Vitrimer-like shape memory polymers (SMPs) combine the vitrimer-like behavior (associated with dissociative covalent adaptable networks) and SME, and can be utilized to achieve many novel functions that are difficult to be realized by conventional polymers. In the first part of this paper, a commercial polymer is used to demonstrate how to characterize the vitrimer-like behavior based on the heating-responsive SME. In the second part, a series of cases are presented to reveal the potential applications of vitrimer-like SMPs and their composites. It is concluded that the vitrimer-like feature not only enables many new ways in reshaping polymers, but also can bring forward new approaches in manufacturing, such as, rapid 3D printing in solid state on space/air/sea missions.

Room-Temperature Solid-State UV Cross-Linkable Vitrimer-like Polymers for Additive Manufacturing

“…Recall the DSC result of the un-cross-linked sample in Figure S3b in Supplementary . Apparently, this type of room-temperature UV cross-linkable vitrimer is different from that reported in [ 6 ], which melts upon heating to approximately 65 °C (based on DSC) and then the reversible cross-linking starts to gradually disappear from approximately 80 °C (according to DMA). Only upon heating to approximately 105 °C does it becomes easy to flow (according to DMA).…”

“…Without UV cross-linking, the quadruple hydrogen bond of UPy, which is reversible upon thermal cycling, indicates that UPy-HTPB-UPy is essentially a vitrimer-like polymer. However, slightly different from that reported in [ 6 ], UPy-HTPB-UPy can be cross-linked at room temperature, and it becomes easy to flow upon heating to the temperature that the quadruple hydrogen bond disappears (refer to Figure S3 in the supplementary material and Figure 5 a).…”

“…Recently, rapid VAM in solid state has been demonstrated using a special thermal gel [ 4 ]. For a hard polymeric version, UV cross-linkable vitrimer has been suggested as the material [ 6 ]. The material developed here is just right for proof-of-the-concept.…”

“…This feature is applicable to most polymeric materials, including most thermset [ 5 ], and ensures high dimensional accuracy after the un-cross-linked part is removed. As for high-strength polymers, UV cross-linkable vitrimer, which has a reversible/dynamic cross-linking network so that it is thermoset at lower temperatures and becomes thermoplastic at higher temperatures, should be the right candidate for rapid solid-state VAM [ 6 ].…”

Rosin-Based Epoxy Vitrimers with Dynamic Boronic Ester Bonds

“…The shape change is reversible, and the process is repeatable, since the thermally induced dynamic exchange reaction is attributed to the reorganization of the cross-linked covalent network [ 55 , 56 ]. Moreover, shape memory cycles [ 57 ] were conducted by DMA ( Figure S3 in Supplementary Materials ). At the initial shape memory cycle, 20% C-FPAE displayed a shape fixation ratio (R f ) of 86% and a shape recovery ratio (R r ) of 59%.…”