Design and characterisation of vitrimer-like elastomeric composites from HXNBR rubber

Vat Photopolymerization 3D-Printing of Dynamic Thiol-Acrylate Photopolymers Using Bio-Derived Building Blocks

As an energy-efficient additive manufacturing process, vat photopolymerization 3D-printing has become a convenient technology to fabricate functional devices with high resolution and freedom in design. However, due to their permanently crosslinked network structure, photopolymers are not easily reprocessed or repaired. To improve the environmental footprint of 3D-printed objects, herein, we combine the dynamic nature of hydroxyl ester links, undergoing a catalyzed transesterification at elevated temperature, with an acrylate monomer derived from renewable resources. As a sustainable building block, we synthesized an acrylated linseed oil and mixed it with selected thiol crosslinkers. By careful selection of the transesterification catalyst, we obtained dynamic thiol-acrylate resins with a high cure rate and decent storage stability, which enabled the digital light processing (DLP) 3D-printing of objects with a structure size of 550 µm. Owing to their dynamic covalent bonds, the thiol-acrylate networks were able to relax 63% of their initial stress within 22 min at 180 °C and showed enhanced toughness after thermal annealing. We exploited the thermo-activated reflow of the dynamic networks to heal and re-shape the 3D-printed objects. The dynamic thiol-acrylate photopolymers also demonstrated promising healing, shape memory, and re-shaping properties, thus offering great potential for various industrial fields such as soft robotics and electronics.

Diketoenamine-based Vitrimers via Thiol-ene photopolymerization

Likened to both thermosets and thermoplastics, vitrimers are a unique class of materials that combine remarkable stability, healability, and reprocessability. Herein, we describe a photopolymerized thiol-ene-based vitrimer that undergoes dynamic covalent exchanges through uncatalyzed transamination of enamines derived from cyclic β-triketones, whereby the low energy barrier for exchange facilitates reprocessing and enables rapid depolymerization. Accordingly, we devised an alkene-functionalized β-triketone, 5,5-dimethyl-2-(pent-4-enoyl)cyclohexane-1,3-dione, which was reacted with 1,6-diaminohexane in a stoichiometrically imbalanced fashion (∼1:0.85 primary amine:triketone). The resulting networks exhibited subambient glass transition temperature (T_g = 5.66°C) by differential scanning calorimetry (DSC). Using a Maxwell stress-relaxation fit, the topology freezing temperature (T_v ) was calculated to be -32°C. Small-amplitude oscillatory shear (SAOS) rheological analysis enabled us to identify a practical critical temperature above which the vitrimer could be successfully reprocessed (T_v,eff ). Via the introduction of excess primary amines, we could readily degrade the networks into monomeric precursors, which were in turn reacted with diamines to regenerate reprocessable networks. Photopolymerization provides unique spatiotemporal control over the network topology, thereby opening the path for further investigation of vitrimer properties. As such, this work expands the toolbox of chemical upcycling of networks and enables their wider implementation. This article is protected by copyright. All rights reserved.

Photopolymerizable Ionogel with Healable Properties Based on Dioxaborolane Vitrimer Chemistry

Ionogels are solid polymer gel networks loaded with ionic liquid (IL) percolating throughout each other, giving rise to ionically conducting solid electrolytes. They combine the mechanical properties of polymer networks with the ionic conductivity, non-volatility, and non-flammability of ILs. In the frame of their applications in electrochemical-based flexible electronics, ionogels are usually subjected to repeated deformation, making them susceptible to damage. It appears critical to devise a simple and effective strategy to improve their durability and lifespan by imparting them with healing ability through vitrimer chemistry. In this work, we report the original in situ synthesis of polythioether (PTE)-based vitrimer ionogels using fast photopolymerization through thiol-acrylate Michael addition. PTE-based vitrimer was prepared with a constant amount of the trithiol crosslinker and varied proportions of static dithiol spacers and dynamic chain extender BDB containing dynamic exchangeable boronic ester groups. The dynamic ionogels were prepared using 50 wt% of either 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide or 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate, both of which were selected for their high ionic conductivity. They are completely amorphous (T_g below -30 °C), suggesting they can be used at low temperatures. They are stretchable with an elongation at break around 60%, soft with Young's modulus between 0.4 and 0.6 MPa, and they have high ionic conductivities for solid state electrolytes in the order of 10^-4 S·cm^-1 at room temperature. They display dynamic properties typical of the vitrimer network, such as stress relaxation and healing, retained despite the large quantity of IL. The design concept illustrated in this work further enlarges the library of vitrimer ionogels and could potentially open a new path for the development of more sustainable, flexible electrochemical-based electronics with extended service life through repair or reprocessing.

Locally controlling dynamic exchange reactions in 3D printed thiol-acrylate vitrimers using dual-wavelength digital light processing

A photolatent transesterification catalyst is applied to locally switch on and control topological rearrangements in 3D printable thiol-acrylate vitrimers.

Digital light processing 3D printing with thiol–acrylate vitrimers

The customized fabrication of soft active devices with self-healing function is demonstrated by 3D printing with vitrimeric thiol–acrylate photopolymers.