Photothermal-induced self-healable and shape memory materials have drawn much attention due to the rapidly growing technical applications and environmental requirements. As epoxy natural rubber (ENR) is a kind of bio-based elastomer with good mechanical properties, weather resistance, and air impermeability, it is of great significance to incorporate ENR with recyclable, photothermal-induced self-healable and shape memory properties. In this study, we report a simple method to cross-link ENR with dodecanedioic acids (DAs) through esterification reaction, and during the cross-linking process, a little aniline trimer (ACAT, a kind of oligoaniline) was added at the same time. Then, the ENR-DA-ACAT vitrimers that were covalently cross-linked with recyclable, self-healable, and multiple responsive properties were obtained, which also possessed various functions. As a result of the transesterification reactions at elevated temperatures, the ENR-based vitrimers possess the ability to be reprocessed and self-healed, and the mechanical properties could be maintained even after three consecutive breaking/mold pressing cycles. Besides, the vitrimer is also responsive to near-infrared (NIR) light and pH with the introduction of ACAT, and we also find that ACAT can be used as a catalyst to accelerate the transesterification reaction. Moreover, it is demonstrated that the ENR-DA-ACAT vitrimer could also be used to construct the reconfigurable shape memory polymer; the shape fixing ratio and shape recovery ratio are both above 95% in the reconfiguration process, and the multistage shape memory performance can also be achieved by NIR irradiation, which will potentially lead to a wide application for ENR in the field of actuators.

Vitrimer is a new class of polymeric materials which can be reprocessed to any shape while being permanently cross-linked. We designed and synthesized a catalyst-free network with poly-(dimethylsiloxane)etherimide (PDMS-NH 2 ), terephthalaldehyde (TA), and tri(2-aminoethyl)amine (TREA) through the condensation reaction between amino groups and aldehyde groups. As a result of the exchange reaction of the dynamic imine bond obtained, this PDMS network exhibits the nature of vitrimer-like material, which is examined by solubility and stress-relaxation experiments, and the relaxation time is as short as 64 s at 130 °C. In addition, the vitrimer-like PDMS is malleable and capable of self-healing, and the mechanical properties can be maintained even after three consecutive breaking/mold pressing cycles. Especially, besides heating, this vitrimer-like PDMS can also be recycled and reshaped at ambient temperature due to the exchange reaction of dynamic imine bond when immersed in water, which will potentially lead to green processing of the elastomers.

A versatile double-network (DN) hydrogel with two noncovalent crosslinked networks is synthesized by multiple hydrogen bonding (H-bonding) interactions. The DN hydrogels are synthesized via a heating-cooling photopolymerization process by adding all reactants of agar, N-acryloyl glycinamide (NAGA) and N-benzylacrylamide (NBAA) monomers, UV initiators to a single water pot. Poly(N-acryloyl glycinamide-co-N-benzyl acrylamide) (P(NAGA-co-NBAA)) with a triple amide in one side group is synthesized via UV-light polymerization between NAGA and NBAA, forming a strong intermolecular H-bonding network. Meanwhile, the intramolecular H-bonding network is formed between P(NAGA-co-NBAA) and agars. The sol-gel phase transition of agars at 86 °C generates the molecular entanglement network. Such a double network enables the hydrogel high self-healing efficiency (about 95%), good shape memory ability, and high mechanical strength (1.1 MPa). Additionally, the DN hydrogel is completely crosslinked by multiple hydrogen bonds (H-bonds) and the physical crosslinking of agar without extra potential toxic chemical crosslinker. The DN hydrogels find extensive applications in the biomedical materials due to their excellent biocompatibility.

A homogenous silicone dielectric elastomer with simultaneously improved dielectric and mechanical properties is synthesized by designing a dual crosslinking network.

The shape memory thermoplastic polyurethane (TPU) generally exhibits a phase-separated structure, in which the hard segments form the hard domains via hydrogen bonds, and plays an important role in shape recovery. However, the physical interaction in the hard domains is always weak, resulting in a permanent deformation and thus decreasing the shape-recovery ability of TPU significantly. In this research, a new type of diol chain extender containing anthracene groups was synthesized, and the photoresponsive anthracene groups were incorporated into the hard segment of TPU. The stability in hard domains and recoverability could be tailored by different UV irradiation times via the photodimerization of anthracene groups, and the shape-recovery ratio and the shape-fixing ratio were still both above 93%, even when the strain reached 270%. More importantly, the shape-free reconfiguration is achieved through the dimerization of anthracene groups under UV irradiation, which achieved free construction of three-dimensional (3D) shapes without templates. Thus, the spontaneous shape change from two-dimensional (2D) to 3D was realized, in combination with melting transition, and the dedimerization of anthracene ensured the recyclability of polyurethane at T = 150 °C. This simple and facile strategy could be used to fabricate the recyclable and photoplasticity shape memory TPU with a high shape-fixing/recovery ratio at large deformation, and it would have a wider range of potential application in stents.

Thermo-reversible elastomers (TRE) can be repeatedly processed and, thus, can reduce the dependence of the petroleum for synthetic rubber. The preparation of TRE is generally carried out in solution, and it requires a long reaction time. These disadvantages limit the large scale preparation of TRE. In the present work, we chose the epoxidized natural rubber (ENR) as the matrix and designed a new method to prepare thermo-reversible, self-healable ENR by a catalyzed ring-opening (RO) reaction of ENR followed by a Diels−Alder (DA) reaction through one-step melt blending for the first time. Furfurylamine (FA) was first grafted onto ENR (ENR−FA) by an RO reaction under the presence of catalyzer, and then bismaleimide (BMI) was added to induce the cross-linking of ENR−FA via DA reaction, which can be easily realized during melt blending. As the DA reaction is reversible at different temperatures, the mechanical properties of thermoreversible ENR (TRENR) could be tailored by the ratio of FA to BMI. The TRENR is recyclable twice by compression molding, while retaining 90% of its mechanical properties after the first recycling. In addition, the as-prepared TRENR exhibits self-healing ability. The preparation of TRENR was carried out in a Haake rheomixer batch mixer with a short reaction time, and it requires no solvent and does not produce a stimulating smell. This new technique is promising in industry for rubber recycling and large-scale preparation of TRE in an environmentally friendly method.

Dielectric elastomers (DEs) have attracted much attention due to their application prospects in biomimetic actuated devices, it is still a big challenge to prepare DEs with high dielectric constants (ε′) and low dielectric losses (tan δ). This work reports highly stretchable poly(propylene-monothiocarbonate)/graphene oxide (PPMTC/GO) dielectric composites with high ε′ and low tan δ via a simple solution-mixing process. The PPMTC with repeated thiocarbonate units enhances the interfacial polarizations with GO, leading to a high ε′ (up to 12). Meanwhile, the hydrogen bonding interactions of PPMTC and GO improve the dispersion of GO in the polymer matrix and thus decrease tan δ (∼0.07). Interestingly, the PPMTC/GO composites also possess excellent shape-memory performance, especially under large deformations (about 50%), with both the fixing ratio (R f ) and recovery ratio (R r ) more than 90%. In addition, the ultimate tensile strength is about 6.5 MPa for the neat PPMTC and over 7.0 MPa for its composites, and the elongation at break for all the samples is over 700%. Thus, it provides an alternative method to the fabrication of DEs.

The key to achieving homogenous dielectric elastomers (DEs) with broader application prospects is obtaining a high dielectric constant (ε′), excellent mechanical properties, and self-healing abilities.