Conventional epoxy polymers are constructed by petro-based resources that are toxic and nonrenewable, and their permanent cross-links make them difficult to be reprocessed, reshaped, and recycled. In this study, a unique eugenol-derived epoxy (Eu-EP) is synthesized, and then vitrimeric materials are prepared by reacting Eu-EP with succinic anhydride (SA) at various ratios (1:0.5, 1:0.75, and 1:1) in the presence of zinc-containing catalysts. All vitrimers exhibit excellent shape changing, crack healing, and shape memory properties. Although vitrimers with 1:0.75 and 1:1 ratios cannot be physically reprocessed, they can be well reprocessed by the chemical method of being simply decomposed in a benign ethanol solution without loading additional catalyst. The collected decomposed polymers can form vitrimers again after exposure at 190 °C for 3 h. This work combines the concepts of vitrimer preparation, chemical recycling, and biobased polymer together, which would bring a feasible way to satisfy the demands of sustainability.

The design of high glass transition temperature (T g ) thermoset materials with considerable reparability is a challenge. In this study, a novel biobased triepoxy (TEP) is synthesized and cured with an anhydride monomer in the presence of zinc catalyst. The cured TEP exhibits a high T g (187 °C) and comparable strength and modulus to the cured bisphenol A epoxy. By adopting the vitrimer chemistry, the cross-linked polymer materials are imparted significant stress relaxation and reparability via dynamic transesterification. It is noted that the reparability is closely related to the repairing temperature, external force, catalyst content, and the magnitude of rubbery modulus of the sample. The width of the crack from the cured TEP can be efficiently repaired within 10 min. This work introduces the first high-T g biobased epoxy material with excellent reparability and provides a valuable method for the design of high-T g self-healing materials suitable for high service temperature.

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Functional polymers are intelligent materials that can respond to a variety of external stimuli. However, these materials have not yet found widespread real world applications because of the difficulties in fabrication and the limited number of functional building blocks that can be incorporated into a material. Here, we demonstrate a simple route to incorporate three functional building blocks (azobenzene chromophores, liquid crystals, and dynamic covalent bonds) into an epoxy-based liquid crystalline network (LCN), in which an azobenzene-based epoxy monomer is polymerized with an aliphatic dicarboxylic acid to create exchangeable ester bonds that can be thermally activated. All three functional building blocks exhibited good compatibility, and the resulting materials exhibits various photomechanical, shape memory, and self-healing properties because of the azobenzene molecules, liquid crystals, and dynamic ester bonds, respectively.

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A smectic main-chain liquid crystalline elastomer (LCE), with controlled shape memory behavior, is synthesized by polymerizing a biphenyl-based epoxy monomer with an aliphatic carboxylic acid curing agent. Microstructures of the LCEs, including their liquid crystallinity and crosslinking density, are modified by adjusting the stoichiometric ratio of the reactants to tailor the thermomechanical properties and shape memory behavior of the material. Thermal and liquid crystalline properties of the LCEs, characterized using differential scanning calorimetry and dynamic mechanical analysis, and structural analysis, performed using small-angle and wide-angle X-ray scattering, show that liquid crystallinity, cross-linking density, and network rigidity are strongly affected by the stoichiometry of the curing reaction. With appropriate structural modifications it is possible to tune the thermal, dynamic mechanical, and thermomechanical properties as well as the shape memory and thermal degradation behavior of LCEs. ■ INTRODUCTIONShape memory polymers (SMP) are a category of smart materials that are able to return to their original shape from a deformed state when exposed to external stimuli. SMPs generally consist of cross-linked polymer networks, which determine the permanent shape of the material, and switching segments, which can be oriented and solidified to fix a temporary shape. 1 The shape recovery is driven by the entropic force of the switching domains which tend to gain entropy and return to a random conformation when undergoing phase transitions, such as glass transition, liquid crystalline (LC) transition, and melting transition. 2,3 Liquid crystalline elastomers (LCE) represent a special class of SMPs that are defined by a reversible LC phase transition and a unique coupling between LC mesogens and polymer networks. They exhibit reversible shape change when exposed to external stimuli, such as heat, 4 light, 5−8 or magnetic field, 9,10 which makes them excellent candidates for artificial muscles, sensors, lithography substrates, and shape memory materials. 11−16 A number of LCEs with different LC phases and network structures have been synthesized and characterized, including nematic main-chain, 17−19 smectic main-chain, 20,21 nematic sidechain, 22,23 and smectic side-chain LCEs. 24−26 These materials exhibit a wide variety of shape memory and actuating behaviors. However, in spite of their promising properties and remarkable potential, practical applications of LCEs are limited because of the difficulties encountered when tailoring thermal transition temperatures and thermomechanical properties of the materials for end-use applications. Several methods have been proposed to prepare LCEs with tunable shape memory properties. A smectic main-chain LCE has been designed and synthesized through copolymerization of two benzoate-based vinyl monomers with different LC phase transition temperatures. 27 It has been shown that both LC transition and thermomechanical properties of LCEs could be tailored by changing the ...

Disulfide exchange and thiol–disulfide interchange reactions allow for reprocessing and recycling of azobenzene-based liquid crystalline networks.