Reversible Diels-Alder Chemistry Research Articles

Structure–Property Relationships of Self-Healing Polymer Networks Based on Reversible Diels–Alder Chemistry

Structure–Property Relationships of Self-Healing Polymer Networks Based on Reversible Diels–Alder Chemistry

Comparison of thermoresponsive Diels-Alder linkers for the release of payloads from magnetic nanoparticles via hysteretic heating

Investigation into the use of thermally reversible Diels-Alder chemistry coupled with magnetic iron oxide nanoparticles has grown over the last decade. This technology has been used for a variety of applications such as thermoresponsive materials, catalytic chemistry, and drug delivery systems. In this study, we evaluate two distinct thermally labile Diels-Alder linkers for the release of payloads from the surface of magnetic iron oxide nanoparticles. Density functional theory (DFT) computational predictions of the Gibbs free energy and enthalpy reaction barriers were performed and revealed a dramatic difference in reverse energy barriers between the two linkers. These thiophene-based cycloadducts were then synthesized, conjugated to the surface of iron oxide nanoparticles, and characterized by NMR and ESI-MS. The results of the modeling were confirmed when the functionalized nanoparticles were subjected to immersion heating and the payload release rates observed were in agreement with the DFT calculations. Similarly, AMF-RF hysteretic heating of the functionalized nanoparticles revealed payload release rates that correlated with the DFT calculations and the data from the heat immersion studies. Together, these results indicate that these distinct thermally labile Diels-Alder linkers can be used to fine-tune the kinetics of payload release from nanoparticles.

A self-healable polymer binder for Si anodes based on reversible Diels–Alder chemistry

Polymeric binders that interact strongly with Si can overcome a rapid capacity fading caused by its large volumetric changes (around 400%) during the charge-discharge process when Si was used as a next generation anode material in lithium ion batteries (LIBs). Among them, poly(acrylic acid) (PAA) is known to improve cell cyclability by enhancing the mechanical properties of Si through hydrogen bonding. This study added 1,6-bismaleimide (BMI) as a crosslinker to furfurylamine-functionalized poly(acrylic acid) (FPAA) and formed a 3D crosslinked polymer network based on thermal Diels–Alder (D–A) click chemistry, which was then used as a new polymer binder for the Si anode. Having the reversible nature of D–A chemistry, the crosslinked network exhibited a self-healing property. The Si electrode with the D-A-adduct binder (DA-PAA) had excellent adhesive strength with regards to Si. After 200 cycles, it recorded a reversible capacity of 1076 mAh g−1 and a high Coulombic efficiency of 99.7%, both of which were much higher than the values obtained for typical commercial binders.

Eco-friendly, self-repairing polymer materials based on reversible Diels-Alder chemistry

The recyclability and reuse of materials are essential for satisfying the current demand for polymers while alleviating the impact on the environment. Herein, a series of self-repairing polymeric materials were synthesized by exploiting the reversibility of the Diels-Alder (DA) reaction. The main polymer chains were composed of polyethylene glycol diglycidyl ether (PEGDGE) and polypropylene glycol diglycidyl ether (PPGDGE). The DA reaction kinetics and the mechanism of retro-Diels–Alder (rDA) reaction were studied with Fourier transform infrared (FTIR) spectroscopy. The cross-linking conversion rate exceeded 80% after 100 min and reached 99% after 50 h at 65 °C, which is remarkably higher and faster than previous studies. The polymeric material was shown to have excellent reusability and high-temperature self-repairing properties. In addition, the polymer was also capable of performing high-temperature shaping and solvent recovery shaping.

Thermally reversible rubber-toughened thermoset networks via Diels–Alder chemistry

In this work we present a reversible and toughened thermoset system based on the covalent incorporation of a furane functionalized ethylene–propylene rubber (EPM-Fu) into a thermoset furane functionalized polyketone (PK-Fu) via Diels–Alder (DA) reversible cross-linking with bismaleimide (b-MA). FT-IR and DSC analyses proved the reversible interaction between PK-Fu and EPM-Fu with b-Ma via DA and r-DA sequence. Likewise, thermo-mechanical experiments (DMTA) indicated the re-workability of the material with no evident differences in elastic and loss modulus after several heating cycles and recycling procedures. Moreover, a considerable increase in the softening point (tangentδ) was also found for the higher toughened system containing 12wt% of EPM-Fu (neat thermoset T=137°C whereas toughened thermoset T=155°C). A two-fold increase in IZOD impact strength compared to the neat thermoset (up to 27J/m) was also recorded by the toughened system. Overall, this approach clearly indicates that fully thermally reversible and toughened thermosets can be realized starting from mixtures of furan functionalized polyketone and EPM rubber, cross-linked via reversible Diels–Alder chemistry.

Reversible Diels‐Alder Chemistry as a Modular Polymeric Color Switch

A fully reversible polymeric color-switch system based on reversible Diels-Alder chemistry between cyclopentadienyl capped polymers and highly electron deficient dithioesters is described. The detailed reaction progress could be mapped on a molecular level for several complete switching cycles and was underpinned by an ESI-MS study.

Controlling Surface Energy and Wetability with Diels−Alder Chemistry

Reversible Diels-Alder chemistry was utilized to manipulate the surface energy of glass substrates. Hydrophobic dieneophiles were prepared and attached to glass slides and capillaries to yield a nonwetting surface. Thermal treatment of the surfaces cleaved the Diels-Alder linkage, and resulted in the fabrication of a hydrophilic surface. Preliminary analysis utilized contact angle (CA) measurements to monitor the change in surface energy, and observed a hydrophilic state (CA - 70 +/- 3 degrees) before attachment of the dieneophile to a hydrophobic state (CA - 101 +/- 9 degrees) followed by regeneration of the hydrophilic state (CA - 70 +/- 6 degrees) upon cleavage of the Diels-Alder linkage. The treatments were then applied to glass capillaries, with effective treatment confirmed by fluid column measurements. Patterned treatments were also demonstrated to provide effective flow gating. Finally, attempts to create self-pressurizing capillaries were unsuccessful due to pronounced contact angle hysteresis for the hydrophobic surface treatment.

Room Temperature Dynamic Polymers Based on Diels–Alder Chemistry

Dynamers based on reversible Diels-Alder chemistry have been obtained and shown to undergo dynamic exchange at room temperature. Their study in solution by small-angle neutron scattering indicated the formation of long and highly flexible chains. Polydispersed molecules gave T(g) values below room temperature, permitting the generation of a dynamic elastomer upon introduction of a dynamic cross-linking agent. The use of a system with a low equilibrium constant gives access to materials with interesting self-healing properties.

Thermoresponsive, Optically Active Films Based On Diels–Alder Chemistry

Reversible Diels-Alder chemistry was exploited to develop polymer films in which a change in optical clarity can be thermally triggered. SiO 2 nanoparticles of various sizes were functionalized with maleimido moieties. A furyl-terminated poly(ethylene glycol) linker was prepared and tethered to the SiO 2 nanoparticles via a Diels-Alder (DA) linkage. The pegylated SiO 2 nanoparticles were randomly distributed within a poly(methyl methacrylate) (PMMA) matrix, resulting in an optically transparent film. Annealing the film cleaves the DA linkage and effectively renders the SiO 2 particles immiscible within the PMMA matrix creating a driving force for particle aggregation. The large aggregates were able to scatter light and resulted in an optically opaque film.

Reversible Diels−Alder Reactions for the Generation of Dynamic Combinatorial Libraries

Condensation reactions between various dienes and dienophiles have been screened for reversibility. Functionalized fulvenes, bearing in particular biological groups, and cyanolefins have been found to react rapidly and reversibly, in the temperature range from -10 to +50 degrees C. These results pave the way for the development of dynamic combinatorial libraries based on reversible Diels-Alder chemistry.