Bio‐based epoxy vitrimers: Reprocessibility, controllable shape memory, and degradability

Abstract

The research activities in the development of recyclable and reprocessable covalently crosslinked networks, and the construction of polymers from renewable resources are both stemmed from the economical and environmental problems associated with traditional thermosets. However, there is little effort in combination of these two attractive strategies in material designs. This article reported a bio‐based vitrimer constructed from isosorbide‐derived epoxy and aromatic diamines containing disulfide bonds. The resulted dynamic epoxy resins showed comparable thermomechanical properties as compared to similar epoxy networks cured by traditional curing agent. Rheological tests demonstrated the fast stress relaxation of the dynamic network due to the rapid metathesis of disulfide bonds at temperature higher than glass transition temperature. This feature permitted the recycling and reprocessing of the fragmented samples for several times by hot press. The dynamic epoxy resins also exhibited shape‐memory effect, and it is demonstrated that the shape recovery ratio could be readily adjusted by controlling the stress relaxation in the temporary state at programming temperature. Moreover, the degradability of the dynamic epoxy resins in alkaline aqueous solution was also demonstrated. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1790–1799

Reprogrammable Permanent Shape Memory Materials Based on Reversibly Crosslinked Epoxy/PCL Blends

“…As observed in Figure 8a, the modulus decreased with the addition of DSS. This result matches with literature data, where the lower modulus was also attributed to the presence of labile disulfide bonds [34].…”

“…As observed, the modulus after the annealing After the film was ground, it was placed in a mold and a pressure of 150 bars was applied for 1 h at 125 • C. Figure 13C shows the image of the obtained film. As observed, the ground material was able to produce a film, which confirmed that the material could be reprocessed due to the disulfide linkage [33,34]. This was exclusively possible in the sample that only contained DSS curing agent.…”

“…As observed in the DMA results, this network had a higher mobility because of the dynamic nature of the crosslinker. In order to change the permanent shape of the material, it was given a new shape by placing it in the oven at 100 • C, for 5 h. The idea was that the internal stress was relaxed by disulfide exchange at higher temperatures and a new permanent shape could be programmed for a pure epoxy material, as demonstrated in the literature [34].…”

“…For example, disulfide linkages have been introduced in epoxy prepolymers [32] or via crosslinking using 4.4'-dithiodianiline [33]. Hu and co-workers [34] have also used this curing agent to crosslink a bio-based epoxy resin. This last material shows shape memory properties but in addition, due to the disulfide linkages, the permanent shape of this material can be changed, which can be of great interest in the development of novel smart materials.…”

Linear Viscoelasticity and Flow of Self-Assembled Vitrimers: The Case of a Polyethylene/dioxaborolane System

“…1 Since then, the literature has focused on altering the exchange reaction (either catalytically controlled or catalyst-free) and adapting chemistries to different polymer backbones. 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27 Other studies explored the properties of vitrimer composites and the addition of nondynamic cross-links to the network. 14,28,29,30,31,32,33,34,35 These research efforts established that modifying vitrimer chemistry provides a pathway for tuning mechanical properties, 36,37,38 stress relaxation, 39,40,41,42 shape memory, 43,44,45 and the ability to self-heal and adhere to other materials.…”