Biobased Transesterification Vitrimers

Fast-Curing of Liquid Crystal Thermosets Enabled by End-Groups Regulation and In Situ Monitoring by Triboelectric Spectroscopy

The development of high-performance polymer is crucial for the fabrication of triboelectric nanogenerators (TENGs) used in extreme conditions. Liquid crystal polyarylate thermosets (LCTs) demonstrate great potential as triboelectric material by virtue of exceptional comprehensive properties. However, there are only a few specific end-groups like phenylethynyl matching the LCT polycondensation temperature (above 300 °C). Moreover, the excellent properties of LCTs rely on the crosslinked network formed with long curing time at high temperature, restricting their further application in triboelectric material. Herein, a fast-curing LCT is designed by terminating with 4-maleimidophenol possessing appropriate reactivity. The resultant LCT (MA-LC-MA) exhibits much lower polycondensation temperature (250-270 °C) and curing temperature of 300 °C within only 1 min compared to typical LCTs (cured at 370 °C for 1 h). Furthermore, the cured MA-LC-MA retains a high glass transition temperature of 135 °C, storage modulus of 6 MPa even at 350 °C, and great electrical output performance. Additionally, triboelectric measurement related to the dielectric properties that vary with crosslinked network is innovatively utilized as an analysis technique of curing progress. This work provides a new strategy to design high-performance TENGs and promotes the development of next generation thermosets in extreme conditions.

Rapidly Self-Healable and Melt-Extrudable Polyethylene Reprocessable Network Enabled with Dialkylamino Disulfide Dynamic Chemistry

Catalyst-free, radical-based reactive processing is used to transform low-density polyethylene (LDPE) into polyethylene covalent adaptable networks (PE CANs) using a dialkylamino disulfide crosslinker, BiTEMPS methacrylate (BTMA). Two versions of BTMA are used, BTMA-S2, with nearly exclusively disulfide bridges, and BTMA-Sn, with a mixture of oligosulfide bridges, to produce S2 PE CAN and Sn PE CAN, respectively. The two PE CANs exhibit identical crosslink densities, but the S2 PE CAN manifests faster stress relaxation, with average relaxation times ∼4.5 times shorter than those of Sn PE CAN over a 130 to 160 °C temperature range. The more rapid dynamics of the S2 PE CAN translate into a shorter compression-molding reprocessing time at 160 °C of only 5 min (vs 30 min for the Sn PE CAN) to achieve full recovery of crosslink density. Both PE CANs are melt-extrudable and exhibit full recovery within experimental uncertainty of crosslink density after extrusion. Both PE CANs are self-healable, with a crack fully repaired and the original tensile properties restored after 30 min for the S2 PE CAN or 60 min for the Sn PE CAN at a temperature slightly above the LDPE melting point and without the assistance of external forces.

New Advances in Covalent Network Polymers via Dynamic Covalent Chemistry

Covalent network polymers, as materials composed of atoms interconnected by covalent bonds in a continuous network, are known for their thermal and chemical stability. Over the past two decades, these materials have undergone significant transformations, gaining properties such as malleability, environmental responsiveness, recyclability, crystallinity, and customizable porosity, enabled by the development and integration of dynamic covalent chemistry (DCvC). In this review, we explore the innovative realm of covalent network polymers by focusing on the recent advances achieved through the application of DCvC. We start by examining the history and fundamental principles of DCvC, detailing its inception and core concepts and noting its key role in reversible covalent bond formation. Then the reprocessability of covalent network polymers enabled by DCvC is thoroughly discussed, starting from the significant milestones that marked the evolution of these polymers and progressing to their current trends and applications. The influence of DCvC on the crystallinity of covalent network polymers is then reviewed, covering their bond diversity, synthesis techniques, and functionalities. In the concluding section, we address the current challenges faced in the field of covalent network polymers and speculates on potential future directions.

Recycling of Polydicyclopentadiene Enabled with N-Coordinated Boronic Ester Bonds

In this contribution, the transformation of polydicyclopentadiene (PDCPD) from thermoset into vitrimer is introduced. First, two N-coordinated diboronic diols are successfully synthesized via the reaction of N,N,N-tri(2-hydroxyethyl)amine and/or N,N,N",N"-tetrakis(2-hydroxyethyl)ethylene diamine with 4-(hydroxymethyl) phenylboronic acid and then they are transformed into two N-coordinated cyclic boronic diacrylates. The latter two dienes carrying electron-withdrawing substituents are used for the ring opening insertion metathesis copolymerization (ROIMP) of dicyclopentadiene to afford the crosslinked PDCPD. In the crosslinked PDCPD networks, N-coordinated cyclic boronic ester bonds are integrated. It is found that the as-obtained PDCPD networks displayed the excellent reprocessing properties. In the meantime, the fracture toughness is significantly improved. Owing to the inclusion of N-coordinated cyclic boronic ester bonds, the modified PDCPDs have the thermal stability much superior to plain PDCPD. The results reported in this work demonstrate that PDCPD can successfully be transformed into the vitrimers via the introduction of N-coordinated cyclic boronic ester bonds.

Oxime metathesis: tuneable and versatile chemistry for dynamic networks

Oxime chemistry has emerged as a versatile tool for use in a wide range of applications. In particular, the combination of oximes with esters and urethanes has enabled the realisation of Covalent Adaptable Networks (CANs) with improved and tunable dynamic properties. Nevertheless, an exclusively oxime-based chemistry has not yet been explored in the fabrication of CANs. In this work, we investigate the mechanism of the acid-catalysed dynamic exchange of oximes. We propose a metathesis mechanism that is well supported by both experimental and computational studies, which highlight the importance of the substituent effect on the exchange reaction kinetics. Then, as a proof of concept, we incorporate oxime groups into a cross-linked polymeric material and demonstrate the ability of oxime-based polymers to be reprocessed under acid catalysis while maintaining their structural integrity.

Fully Biobased Degradable Vitrimer Foams: Mechanical Robust, Catalyst-Free Self-Healing, and Shape Memory Properties

Thermosetting foams have limited capabilities for recycling, reprocessing, or reshaping. Moreover, most of the foaming agents currently employed in these foams are derived from organic compounds sourced from petrochemicals, thereby posing a significant environmental threat due to heightened pollution. To solve these problems, a fully biobased degradable vitrimer foam (EPC-X) was fabricated using an environmentally friendly all-in-one foaming strategy by cross-linking epoxidized malepimaric anhydride (EMPA), 1,5-diaminopentane (PDA), and 1,5-diaminopentane carbamate (PDAC) as a latent curing-blowing agent. To our delight, the vitrimer foams exhibit excellent mechanical properties (2.86 ± 0.11 MPa compressive strength) owing to their unique rigid rosin backbone and cross-linking networks. The presence of dynamic β-hydroxy ester bonds and the self-catalytic behavior of tertiary amine groups facilitate network rearrangement without requiring additional catalysts, thereby resulting in the development of EPC-X with rapid self-healing and shape memory properties. The self-healing foam could support a weight of 500 g (approximately 562 times its own mass). Moreover, these high-performance vitrimer foams can also be easily degraded in an ethanolamine (EA) or NaOH solution under mild conditions. Such a design strategy offers an alternative approach for developing superior degradable and thermal stimuli-responsive thermosetting foams.

Structure and thermal behavior of biobased vitrimer of lactic acid and epoxidized canola oil

Biobased vitrimers were obtained from epoxidized canola oil (ECO) and lactic acid (LA) using zinc acetate (ZnAc) and ZnAl-layered double hydroxide (ZnAl) in the proportions of 1 and 2 wt% as transesterification catalysts. Reactions containing ECO and LA showed an average enthalpy of cure of approximately 85 mJ mg-1 and materials cured in the presence of the catalysts showed lower enthalpies of cure and decrease in the material gel content. ECO-LA reaction generated materials with rubber-like properties with Tg ranging from -15 °C to -23 °C, where the material without a catalyst showed the higher Tg value. The presence of catalysts gave the material vitrimer properties, with the softening point associated with transesterification reactions and topology freezing temperature transition at temperatures (Tv) between 195-235 °C.

Development and Digital Light Processing 3D Printing of a Vitrimer Composed of Glycerol 1,3-Diglycerolate Diacrylate and Tetrahydrofurfuryl Methacrylate

The development of biobased reshapable and repairable vitrimers has received extensive attention due to the growing focus on an environmentally friendly society. Therefore, the objective of this research was to synthesize sustainable polymers with an environmentally friendly strategy combining the benefits of renewable resources, UV curing, and vitrimers. Two biobased monomers, glycerol 1,3-diglycerolate diacrylate and tetrahydrofurfuryl methacrylate, were chosen for the preparation of UV-curable resins and tested by real-time photorheometry and RT-FTIR spectroscopy to determine their suitability for digital light processing (DLP) 3D printing. DLP 3D-printed polymer showed shape memory, weldability, and repairability capabilities by triggering the dynamic transesterification process at high temperatures. The vitrimer with a weight ratio of 60:40 of glycerol 1,3-diglycerolate diacrylate and tetrahydrofurfuryl methacrylate showed shape memory properties with a recovery ratio of 100% and a 7-fold improved tensile strength compared to the original sample, confirming efficient weldability and repairability.