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A novel dynamic network was successfully prepared via self-complementary quadruple hydrogen bonding through Upy-telechelic poly(tetremethylene ether) glycol (PTMEG) and four-arm star-shaped poly(ε-caprolactone) ((4)PCL) precursors. The structure and the dynamic feature were identified by FT-IR and (1)H NMR. The differential scanning calorimetry (DSC) analysis indicated that the crystalline PCL and PTMEG segments show a separated melting peak, and the aggregation of Upy dimer was also observed. The dynamic mechanical analyzer (DMA) test reveals that the storage modulus of the network drops evidently across the thermal transition. These characteristics of the network ensure that it exhibits a triple-shape effect, and the composition of the network influences the performance of shape memory effect. The variation of the fixing ratio of the network in each deformation step is quite according to the crystallinity of the dominant segment. The reversibility of the quadruple hydrogen bonding between Upy dimer endues the network with self-healing capacity, and the damage and healing test of the network revealed that increasing the content of the PTMEG segment will be of benefit to self-healing performance.

This work details a novel polyurethane liquid crystal elastomer (PULCE) with exchangeable carbamate functional groups that enable programming of a uniformly aligned monodomain sample through the application of external stress and simultaneous activation of dynamic bond exchange of the carbamate. PULCEs were synthesized using a thiol-Michael addition reaction, and the reversion of the carbamate group was observed by real-time FT-IR and mechanical analysis. Two independent phase transitions (isotropic–nematic and nematic–smectic) were employed to actuate two-way autonomous strains and multiple shape memory effects in a single system. In addition, thermally activated bond exchange engineered into the network transformed the permanent configuration of the material into various complex shapes. The programmed network topology and bond exchange conditions controlled the two-way autonomous shape changes. Coupling the shape memory effect of the polymer network with the plasticity induced by the thermally activated dynamic covalent chemistry in shape changing and shape memory materials will expand their applications and capabilities in emerging multifunctional devices.

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Based on Diels-Alder reaction, linear bisfuranic terminated poly(tetramethylene oxide) and poly(p-dioxanone) were crosslinked by tris(2-maleimide ethyl)amine; this process was fully reversible under moderate conditions. All of the results indicate that the conetwork possesses the typical advantages of chemical and physical crosslinking, peculiar thermal invertibility, shape memory effect and self-healability.As a most promising intelligent material, shape memory polymers (SMPs) have the capability of changing the shape in response to various external stimuli. 1-3 This characteristic offers SMPs a wide range of applications. 4-7 Conventionally, thermally induced SMPs with one thermally reversible transition can only memorize one temporary shape on a single shape memory cycle, named dual-shape memory polymers. 8 To widen the application of shape memory polymers, different types of SMPs were synthesized. 9-16 The multishape memory effect, referring to the ability of SMPs to memorize at least two temporary shapes in only one shape memory cycle, is currently attracting considerable interest due to its ability to provide an additional dimension to the technical potential of SMPs. Actually, multi-shape memory effects are achievable simply by introducing an additional reversible phase transition, which has been experimentally demonstrated 13 and theoretically proved. 14 From a molecular design standpoint, it is not an arduous task to introduce two distinctive and reversible phases into a polymer to achieve a triple-shape polymer. SMPs meeting this requirement have been reported and the two T trans are T m and T g of SMPs. However, they all have one thing in common: the original shape is defined by netpoints resulting from the chemical crosslinking, 13-20 which is more durable due to its stronger network structure of covalent bonds, and it can result in the SMPs exhibiting excellent shape memory properties such as higher shape recovery and higher fixity ratios compared with physically crosslinked SMPs. 1,19-22 But there is a requirement to address the problem of the chemically crosslinked SMPs, that is, they are not easy to be reprocessed, which would limit the list of applications of shape memory polymers. We therefore designed and developed a novel triple-shape network based on thermally reversible chemical crosslinking. At least two different polymer segments were introduced to build the network with separated switching domains which were associated with two individual transition temperatures (T g or T m ), dominating the temporary shape B and shape C, respectively. The crosslinking determined the permanent shape A.Unlike the traditional triple-shape network, in this work, thermally reversible Diels-Alder (D-A) cycloaddition 22-24 was selected to crosslink the linear bisfuranic terminated poly(tetramethylene oxide) (PTMEG-BF) and poly(p-dioxanone) (PPDO-BF) with tris(2-maleimide ethyl)amine, considering that not only PPDO 25,26 and PTMEG 27 have outstanding biocompatibility, which makes them good candidates for biomate...