Thermoset Shape‐Memory Polyurethane with Intrinsic Plasticity Enabled by Transcarbamoylation

Abstract

Thermoset polymers are knownf or their superior thermomechanical properties,b ut the chemical crosslinking typically leads to intractability.T his is reflected in the great differences between thermoset and thermoplastic shapememory polymers;t he former exhibit ar obust shape memory but are not capable of redefining the permanent shape.C ontrary to current knowledge,w er eveal here that ac lassical thermoset shape-memory polyurethane is readily capable of permanent reshaping (plasticity) after atopological network rearrangement that is induced by transcarbamoylation. By employing the Jianzhi technique (also knowna s kirigami), unexpected shape-shifting versatility was observed for this otherwise classical material. As the essential carbamate moiety in polyurethanes is one of the most common polymer building units,w ea nticipate that our finding will have significant benefits beyond shape shifting.

Poly(oxime–ester) Vitrimers with Catalyst-Free Bond Exchange

“…Vitrimers are a class of thermally re-processable network polymers, which rely on associative dynamic covalent bond exchange reactions to flow, relax, and recover. Subsequent to the pioneering work of Leibler 1 and co-workers, a series of vitrimers 2 or vitrimer-like 3,4 materials have been developed by different types of dynamic covalent bonding reactions, such as transesterification, 5-10 vinylogous urethane transamidation, 11,12 transcarbamoylation, [13][14][15] olefin metathesis, 16 imine bond exchange, [17][18][19] boronic ester exchange, [20][21][22] alkoxysilane exchange reaction, [23][24][25] Diels−Alder cycloaddition, 26,27 reversible radical chemistry, 28,29 oxime−carbamate transcarbamoylation. 30 and diketoenamine exchange.…”

Site‐Specific Pre‐Swelling‐Directed Morphing Structures of Patterned Hydrogels

“…Without the pre-swelling step,t he patterned gel deformed into ar oll (Figure 4a(ii)), similar to the mode I deformation of gel strip shown in Figure 2a.Byusing apair of masks to direct the site-specific pre-swelling,o ther configurations,such as wavy and cruciform shapes,can be obtained (Figure 4a(iii)a nd Figure 4a(iv)). [39,40] For example,w eprepared square or round loop patterned with high-swelling discs (Figures 4b(i)a nd Figure 4c(i));t he free-swelling (without the pre-swelling step) led to deformation of patterned gels into af our-pointed star and cauliflower-like configurations (Figures 4b-(ii)a nd Figure 4c(ii)), respectively,i n which all domes buckled in the same direction yet constrained by the corner or central non-swelling gels.H owever, selectively pre-swelling led to localized buckling into opposite directions and thus the formation of desired configurations,s uch as the dumbbell-like and cloverleaf-like shapes (Figures 4b(iii) and Figure 4c(iii)). [39,40] For example,w eprepared square or round loop patterned with high-swelling discs (Figures 4b(i)a nd Figure 4c(i));t he free-swelling (without the pre-swelling step) led to deformation of patterned gels into af our-pointed star and cauliflower-like configurations (Figures 4b-(ii)a nd Figure 4c(ii)), respectively,i n which all domes buckled in the same direction yet constrained by the corner or central non-swelling gels.H owever, selectively pre-swelling led to localized buckling into opposite directions and thus the formation of desired configurations,s uch as the dumbbell-like and cloverleaf-like shapes (Figures 4b(iii) and Figure 4c(iii)).…”

“…Chemie impart more deformation freedom, just like the kirigami structures. [39,40] . Them odeled behaviors of patterned hydrogels consisted well with the experimental observations.W e should note that the predefined overall pattern has ad etermining influence on the swelling-induced shape change of the hydrogel as aresult of the geometric confinement.…”

The Past 40 Years of Macromolecular Sciences: Reflections on Challenges in Synthetic Polymer and Material Science

“…Why not extend such detection systems to environmental stress detection, living cell systems, and whole organisms, where subtle changes are simply detected by the reorganization of only a few chemical bonds, primarily transmitted by the individual chain dynamics and bond flexibilities of the attached polymer or networks being essential in tuning and magnifying the initially small response . Vitrimers , reversibly decaying materials at enhanced temperatures as coined by L. Leibler, enable thermodynamic equilibria by reducing initially high kinetic barriers and have been recognized as implementing reversibility of any (labile) chemical bond into a generalized material concept, exploiting the thermal reversibility of blocked isocyanates into PU vitrimers . This could finally lead to thermoset systems of similar quality as needed in, for example, automotive industry or aircraft systems, enabling to regain materials after use by just heating to appropriately higher temperatures.…”