Epoxy Thermosets Research Articles

Synergetic Hybridization Strategy to Enhance the Dynamicity of Poorly Dynamic CO2‐derived Vitrimers achieved by a Simple Copolymerization Approach

AbstractCopolymerization allows tuning polymer's properties and a synergetic effect may be achieved for the resulting hybrid, i.e., outperforming the properties of its parents as often observed in natural materials. This synergetic concept is herein applied to enhance both dynamicity and properties of vitrimeric materials using poorly dynamic hydroxyurethane and non‐dynamic epoxy thermosets. The latter generates activated hydroxyl, promoting exchange reactions 15 times faster than pure polyhydroxyurethanes. This strategy allows obtaining catalyst‐free high‐performance vitrimers from conventional epoxy‐amine formulations and an easily scalable (bio‐)CO2‐based yet poorly efficient dynamic network. The resulting hybrid network exhibits modulus retention superior to 95% with fast relaxation (<10 min). The hydroxyurethane moieties actively participate in the network to enhance the properties of the hybrid. The material can be manufactured as any conventional epoxy formulation. This new strategy to design dynamic networks opens the door to large‐scale circular high‐performance structural carbon fiber composites (CFRP). The CFRP can be easily reshaped and welded from flat plates to complex geometries. The network is degradable under mild conditions, facilitating the recovery and re‐use of high‐added‐value fibers. This accessible and cost‐effective approach provides a versatile range of tunable dynamic epoxides, applicable across various industries with minimal adjustments to existing marketed products.

Ultratough, Robustness, and Reprocessable Thermoset Epoxy Resins Synergistically Enhanced by Hierarchical Coordination Interactions and Dynamic Covalent Networks

AbstractEpoxy resins, ubiquitous and indispensable thermosetting material in various industries, suffer from the resistance to crack initiation, poor ductility, and irreparable permanent cross‐linked network, which hinder their utilization in high‐performance applications and are detrimental to the development of a sustainable economy. However, achieving the trade‐off between toughness, robustness, and reprocessability of epoxy resins remains a formidable challenge. Herein, an epoxy resin that combines ultratoughness, robustness, and reprocessability by incorporating a hierarchical crosslink structure embedded in a transesterification network is reported. The construction of hierarchical coordination structures facilitates formation of dense nano‐hard domains, enabling enhancement of both strength and toughness at multilength scales. As a result, the epoxy resin, integrating covalent adaptable networks with sacrificial non‐covalent networks, exhibits exceptional elongation at break (280%), modulus (1.8 GPa), stress at break (56.3 MPa), and tensile toughness (142 MJ m−3), showcasing its excellent endurance and ability to undergo multiple reprocessability. The application of this epoxy resin in carbon fiber‐reinforced polymer composites further underscores its potential as the resulting HCEV‐CFRPs exhibit unprecedented tensile properties and facilitate multiple non‐destructive recycling of high‐value carbon fiber under mild conditions. This research provides novel design principles for recyclable and high‐performance materials that combine strength and toughness.

Bio-derived epoxy thermosets incorporating imine linkages: Towards sustainable and advanced polymer materials

In the search for sustainable and eco-friendly alternatives, Schiff-based epoxy thermosets are emerging as a promising strategy due to the inherent dynamic and reversible nature of their imine functional groups, which enables thermal reprocessability and chemical recyclability. This article explores the synthesis of Schiff-based epoxy thermosets using sustainable approaches. Starting from vanillin or syringaldehyde, the synthesis involves the incorporation of imine linkages into the epoxy network. A new strategy has been employed by self-polymerization without the use of additional curing agents. This approach conducts to novel thermosets with superior material properties that exceed those reported in previous studies. Thermo-mechanical investigations showed that the designed thermosets have high mechanical properties, with storage moduli at room temperature ranging between 1.5–2.2 GPa, and glass transition values between 138 and 249 °C. Thermal analyses allowed to evaluate the Limit Oxygen Index (LOI) which ranged from 33 % to 36 %, demonstrating excellent flame-retardant properties without the addition of supplementary additives. Their reduced density (0.74–1.09 g/cm3) makes them suitable for applications where weight considerations are critical. These results obtained results place the designed Schiff-based materials as promising candidates for a wide range of high-end applications, particularly in industries that prioritize eco-friendly processes and materials.

Biobased recyclable epoxy composites reinforced with carbon nanotubes for electromagnetic interference shielding and Joule heating

AbstractCurrent epoxy thermosets are facing various challenges such as resource scarcity, environmental concern, and limited functionalities. Here, we present a novel solvent free approach to fabricate multifunctional carbon nanotubes (CNTs) reinforced biobased and recyclable epoxy thermoset composites through precuring in an internal mixer followed by curing in an oven. The epoxy matrix, a covalent adaptable network (CAN) based on dynamic imine bonds, was synthesized from entirely biobased feedstocks, including glycerol triglycidyl ether, vanillin, and 1,10‐diaminodecane. The shear force during precuring facilitated dispersion of CNTs in CAN matrix, allowing for high CNTs loading (up to 20 wt%). The well‐dispersed CNTs not only reinforced mechanical properties of CAN but also introduced new functionalities like electrical conductivity, electromagnetic interference (EMI) shielding capacity, and Joule heating performance. The composite with 20% CNTs exhibited a tensile strength and Young's modulus of 78.1 MPa and 3.07 GPa, respectively, marking a 34.2% and 63.6% improvement over pristine CAN. It also demonstrated a high electrical conductivity of 35.3 S/m, resulting in a remarkable EMI shielding effectiveness (22.8 dB) and excellent Joule heating performance (reaching 131.7°C at 27 V input). Furthermore, these composites are thermally and chemically recyclable due to dynamic imine bonds, promoting sustainability and circular economy.

Constructing piperazine pyrophosphate@LDH@rGO with hierarchical core-shell structure for improving thermal conductivity, flame retardancy and smoke suppression of epoxy resin thermosets

The integration and miniaturization development of electronic devices placed the great demand for epoxy resin (EP) thermosets with excellent thermal management, flame retardancy and electrical insulation. Herein, a multifunctional additive piperazine pyrophosphate@layered double hydroxide@reduced graphene oxide (PPAP@LDH@rGO) with hierarchical core-shell structure was constructed by solvothermal and electrostatic self-assembly methods to meet the above requirements. Profiting from the distinct structure of PPAP@LDH@rGO, the thermal conductivity of EP/PPAP@LDH@rGO reached 0.951 W m−1 K−1 at 7 wt% addition (3 wt% rGO containing), which is 320.8 % increment compared to pristine EP. Meanwhile, when 4 wt% PPAP@LDH@rGO was added, the EP thermoset reached UL-94 V-0 rating during vertical burning tests with the limiting oxygen index of 29.8 % due to the synergistic effect of PPAP, LDH and rGO. The release of hazard products including smoke and carbon monoxide for EP/PPAP@LDH@rGO visibly declined during combustion. Besides, the EP thermosets also well-maintained the electrical insulation and mechanical properties. This work provided an alternative approach for preparing high performance EP thermosets which was suitable to be applied in electronics and electrical fields.

High-homogeneous recyclable self-cured epoxy resins based on imine

The production of high-performance epoxy resins currently depends on combining rigid epoxy oligomers and non-flexible hardeners. However, the high melting points and incompatibilities of raw materials, along with the inhomogeneous crosslinked networks of thermoset resins, challenge the development of high-performance epoxy resins simultaneously enhancing strength and toughness with excellent processing properties. To address this issue, we propose a self-curing strategy to obtain a novel thermosetting epoxy resin by simply melting the epoxy oligomers containing the Schiff base structure. The mechanism of self-cured was also revealed by density functional theory. Remarkably, this method eliminates the need for curing agents, catalysts, or active hydrogen structures. The resulting self-cured epoxy resin (VEP-SC) simplifies processing steps. In particular, VEP-SC forms a more homogeneous cross-linked network and exhibits superior mechanical properties due to the unique preparation method. Compared to traditional thermosetting epoxy cured with a curing agent, the tensile strength, elongation at break, and flexural strength of VEP-SC were 133.4 %, 168.4 %, and 276.2 % higher than those of VEP-MeHHPA, respectively. Furthermore, the Schiff base structure imparts the vitrimeric behavior of self-cured epoxy resin, achieving recyclability. This approach provides innovative solutions for developing versatile and high-performance epoxy resins.

Recyclable fully biobased high-performance epoxy thermosets

Thermosetting polymeric materials play a pivotal role in numerous sectors due to their versatility in tailoring physicochemical and mechanical properties and their exceptional performances. The aim of this study is to design 100 % bio-based high performant and recyclable thermosets. To achieve this goal, a natural and renewable-based epoxy monomer, triglycidyl ether of phloroglucinol (TGPh), was crosslinked with biobased anhydrides to create novel polymeric resins. Through detailed investigations, it was found that the designed materials have storage moduli values at room temperature ranging from 2.1 to 3.4 GPa, with damping factors spanning from 86 °C to 163 °C depending on the nature of the anhydride. Tensile tests corroborated the performant mechanical properties of the designed bio-resins, showing Young's modulus values ranging from 1.2 to 1.5 GPa. Furthermore, the water absorption values are very low, ranging from 0.25 % to 0.35 %. Besides, the designed bio-resins exhibited rapid dissolution in TBD/EG solution, as well as thermo-mechanical reprocessability.

Design of self-healing and anticorrosion epoxy coating with active multiple hydrogen bonds based on grafted polyetheramine

The healing of epoxy coatings in damaged areas significantly influences their service life and protection quality. Intrinsic self-healing coatings, which enable multiple healing cycles without the need for additional functional carriers, have emerged as a promising coating technology. Nevertheless, the cross-linked structure of thermoset epoxy coating system restricts the large-scale migration of molecular chains, posing a significant challenge to achieve intrinsic healing of resin without compromising its mechanical properties. In this study, we report a design scheme for epoxy coating with intrinsic self-healing properties based on active multiple hydrogen bonds. Grafting aminobenzothiazole at the end of polyetheramine D230 chain, the grafted polyetheramine (GD230) was synthesized and served as the auxiliary curing agent, whose accurate molecular structure has been confirmed by different characterizations. The self-healing coating with reversible dynamics network based on hydrogen bonds was prepared by crosslinking through epoxy resin and mixed curing agent of polyetheramine D230 and GD230. Various measurements have been adopted to evaluate the self healing and anticorrosion performance. Results showed that the functional coating with a ratio of 8:2 for D230 to GD230 has satisfied both performances on the steel substrate. After immersion in 3 wt% NaCl solution for 120 days, the impedance value of functional coating still remains about 1010 Ω cm2. After the coating was scratched and immersion for 96 h, the impedance value of functional coating increased by about two orders of magnitude compared to that in blank coating. Mechanical testing and theoretical calculations were used to support dynamic crosslinking model to reveal the self-healing mechanism.

Sustainably sourced and DOPO-derived triols as hardeners for epoxy thermosets: A promising solution to synchronously improve flame retardancy, mechanical strength and toughness

The flammability and brittleness of the diglycidyl ether of bisphenol A (DGEBA)-type epoxy resin greatly restrict its application in electronic appliances and structural materials. However, the synchronous improvement in the flame retardancy, mechanical strength, and toughness of DGEBA-type epoxy thermosets remains a significant challenge. To overcome this challenge, in this study, a sustainably sourced and DOPO-derived triol (DOPO-GL-DCDA) was synthesized from a bio-based material, glycerol 1, 3-diglycerolate diacrylate (GL-DCDA). A series of epoxy thermosets with different phosphorus contents were prepared by introducing DOPO-GL-DCDA into the DGEBA matrix. EP/DOPO-GL-DCDA demonstrated excellent flame retardancy and mechanical properties without compromising transparency. Specifically, EP/DOPO-GL-DCDA-1.0P exhibited a limit oxygen index (LOI) of 34.0 % and a UL-94 V-0 rating, and the total heat release (THR) and peak heat release rate (PHRR) of EP/DOPO-GL-DCDA-1.5P decreased by 36.6 % and 46.8 %, respectively, compared with those of pure EP. In addition, compared with those of pure EP, the tensile strength, impact strength, fracture toughness (KIC), and fracture energy (GIC) of EP/DOPO-GL-DCDA-1.5P increased by 62.8 %, 69.9 %, 62.9 %, and 99.0 %, respectively. Moreover, EP/DOPO-GL-DCDA had better dielectric properties than pure EP. Under the premise of maintaining transparency, this work provided a promising solution to synchronously improve the flame retardancy, mechanical strength, and toughness of epoxy thermosets.

Epoxy-based multifunctional re-bondable polymer with self-healing, shape memory and superb bonding properties

Thermoset epoxy resin-based materials are widely used, but their permanent cross-linked network limits their processability and reusability, which can lead to environmental burdens. In this work, by exploiting the weak reactivity of aniline to design appropriate reaction ratios, we achieved a linear link between the epoxy resin and the curing agent. This linear link, along with the crosslinking points provided by the flexibly branched polyurethanes, avoids the inherent brittleness associated with the highly crosslinked network of conventional epoxy resins. As a result, the adhesive exhibits extraordinary improvements in extensibility and toughness. The lap shear strength, tensile strength and elongation at break reach 11.9 MPa, 14.4 MPa and 607 %, respectively. The fracture toughness is as high as 109.6 kJ/m2, far beyond the existing epoxy adhesives. The synergistic effect of disulfide bonds and hydrogen bonds confers the adhesive with self-healing and repeatable bonding characteristics. The multi-level hydrogen bonding and appropriate phase separation structure are key to optimizing toughness, resulting in excellent comprehensive performance. The introduction of polyurethane not only improves toughness but also enhances the interfacial bonding force between the adhesive and the substrate, broadening the scope of applications. The prepared high-performance polymers provide new insights into reusable epoxy adhesives.

Comparison of the in situ compressive behavior of carbon fibers woven ply laminates exposed to one‐sided heat flux: Thermoplastic versus thermosetting composites

AbstractThis study investigates the influence of a combined thermal heat flux (imposed by a cone calorimeter) and a compressive loading on the deformation and damage mechanisms within quasi‐isotropic carbon fibers reinforced thermoplastic (polyetherether ketone [PEEK] and polyphenylene sulfide [PPS]) and thermosetting (epoxy) laminates. First, thermogravimetric Analyses conducted under nitrogen provide valuable information on the thermal decomposition of these materials depending on the matrix nature (580–510°C and 350°C, respectively) which is a key factor to explain the mechanical behavior under fire conditions. Second, under the same testing conditions (creep loading under a 50 kW/m2 heat flux), the time to failure is about 17 times as high (C/PEEK), twice as high (C/PPS) with respect to C/epoxy laminates. At the ply scale, the exposure of thermoplastic matrices (PEEK and PPS) to a 50 kW/m2 heat flux causes softening and thermal decomposition, facilitating the micro‐buckling of fiber bundles in matrix‐rich areas. At the laminates scale, this mechanism ultimately leads to the formation and propagation of plastic kink bands in the transverse direction. In epoxy‐based laminates, the onset of matrix pyrolysis occurs at lower temperatures (350°C) during thermal aggression, and thermal decomposition has started in all the plies of the laminates. Combined with the low ductility of the epoxy matrix, the compressive response is elastic‐brittle and results from the buckling of 0° plies outside the thermally‐damaged area.Highlights Study on the compression of polymer composites exposed to a 50 kW/m2 heat flux. The influence of the matrix nature (thermoplastic vs thermoset) is discussed. Time to failure is about 17 times higher in C/PEEK compared to C/Epoxy. Plastic kink bands propagate in thermoplastic composites at T > Tg. C/Epoxy laminates undergo buckling outside the thermally damaged area.

Novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties

As one of the most commonly used thermosetting resins, the flammability of epoxy resins (EPs) has become a key factor limiting the expansion of their application range. Herein, a novel phosphorous-containing epoxy monomer (EDPPO) was synthesized using diallyl amine and diphenyl phosphoryl chloride as the starting materials. Subsequently, EDPPO was thermally cured with two diamine hardeners, 4, 4′-diaminodiphenyl sulfone (DDS) and 4,4′-dithiodianiline (DTDA). Additionally, commercial diglycidyl ether of bisphenol A (DGEBA)-type epoxy pre-polymers were cured with DDS and DTDA as comparative samples. The cured EDPPO-based thermosets showed excellent flame-retardant properties coupled with smoke suppression. Specifically, the limiting oxygen index (LOI) for the EDPPO/DDS (P content 6.4 wt.%) reached 32.0 %, and the UL-94 vertical burning test reached a V-0 rating. In addition, the PHRR, THR, and TSP values of EDPPO/DDS were 61.6 %, 49.1 %, and 58.5 % lower than those of DGEBA/DDS, respectively. The flame retardant mechanism analysis indicated that the excellent flame retardancy for cured EDPPO-based thermosets was attributed to the combined modes of action in condensed (promoting the charring capacity) and gaseous phases (quenching the active radicals). More importantly, EDPPO/DDS and EDPPO/DTDA exhibited lower dielectric constant and dielectric loss than DGEBA/DDS and DGEBA/DTDA. This work provided novel phosphorous-containing epoxy thermosets with improved anti-flammability, smoke suppression, and dielectric properties.

SEPS functionalized PEG copolymer for improved toughness without obvious plasticization in epoxy resin

AbstractThe effects of grafting level of polyethylene glycol (PEG) grafted styrene ethylene propylene styrene (SEPS) on the intrinsic brittleness of epoxy thermosets were studied. The SEPS‐g‐PEG block copolymer (BCP) was synthesized by grafting various grafting degree of PEG (i.e., 10%, 20%, 30%, and 40%) on polystyrene (PS) blocks of SEPS following Williamson ether synthesis method. A total of 10 wt% of the BCP modifiers were dispersed in epoxy thermosets. PEG side chains were miscible in the epoxy which formed a uniform BCP dispersion within the epoxy thermoset matrix. As the degree of PEG grafting was increased, the BCP phase was absorbed in the epoxy matrix. This absorption occurred because the increase in PEG grafting provided more miscible PEG chains to bind the BCP and epoxy nanostructures together. The differential scanning calorimeter and dynamic mechanical thermal analysis analyses indicated that BCP toughened epoxy exhibited an improved glass transition temperature (Tg). At a 40% PEG grafting degree in the BCP, the critical stress intensity factor (KIC) and critical strain energy release rate (GIC) increased up to 80% and 180%, respectively. This trend suggested that the energy associated with fractures could be absorbed through the deformation of the softer phases when a load was applied to them.

Enhancing thixotropic properties of epoxy resin and mechanical properties of epoxy resin thermosets by polyethyleneimine functionalized carbon nanotubes

Epoxy resin (ER) thermosets are widely applied in various fields due to their high mechanical strength, thermal stability and chemical corrosion resistance. However, the brittleness of ER thermosets and low thixotropic property of ER matrix largely limits their further development. Here, this article develops branched polyethyleneimine (PEI) functionalized carbon nanotube (PEI@CNT) as high-performance nanofiller for simultaneously strengthening and toughening ER thermosets. Benefiting from good dispersity and rich amine groups of PEI@CNT, effective interfacial bonding between PEI@CNT and ER is achieved. The ER thermoset with 0.5 wt% PEI@CNT shows increase in tensile strength by 24.8 % and fracture elongation by 30.0 % compared with pristine ER thermoset. The enhanced mechanical properties of PEI@CNT modified ER thermosets can be ascribed to the chemical interaction between PEI@CNT and ER matrix as well as the formed crack propagation, which can dissipate a lot of fracture energy, further improving the strength and toughness of the ER composites. More importantly, the thixotropic property of ER matrix is largely improved after adding the PEI@CNT filler. This work reports a high-performance nanofiller for enhancing mechanical properties of ER thermosets and processability of ER matrix.

Exploring anti-corrosion properties and rheological behaviour of tannic acid and epoxidized soybean oil-based fully bio-based epoxy thermoset resins

This research explores the physicochemical attributes of a fully bio-epoxy thermoset aimed at serving as an anti-corrosion coating for safeguarding carbon steel structures in marine environments. Throughout this investigation, various epoxy thermosets formulations, based on epoxidized soybean oil (ESO) and tannic acid (TA), were synthesized by adjusting the initial ratios of epoxide:hydroxyl groups (epoxy:OH). These formulations were subsequently applied onto carbon steel substrates and subjected to thermal curing at moderate temperatures (170 °C) to evaluate their anti-corrosion effectiveness using electrochemical impedance spectroscopy (EIS). The examination of the total impedance values derived from EIS Bode diagrams (>106 Ω) revealed a notable anti-corrosion efficacy that endured over several months of immersion in 3.5 wt% NaCl solutions. In addition to electrochemical assessment, a rheological analysis was conducted to determine the optimal curing temperature for each formulation and to track the evolution of their mechanical properties throughout the curing process. Furthermore, the progression of corrosion at the coating-metal interphase was quantified using samples featuring artificially created notches to facilitate rapid water penetration, reaching the protected surface. Moreover, cross-cut and pull-off adhesion tests were conducted on coatings cured with various epoxide:hydroxyl ratios, yielding exceptional results on carbon steel substrates. Overall, a great potential for anti-corrosion protection has been demonstrated on the developed fully bio-based coatings with tuneable mechanical properties, regarding the initial component ratio, to reach the specific requirements for specific applications.

Enhanced mechanical properties of sandwich panels via integrated 3D printing of continuous fiber face sheet and TPMS core

Sandwich panel structures have widespread applications in various components, owing to their excellent lightweight properties. However, conventional manufacturing methods involve multiple steps, which limits the exploration of innovative sandwich panel structure. In this study, an integrated 3D printing method for continuous fibers reinforced sandwich panel with Triply Periodic Minimal Surface (TPMS) core structure is proposed via Fused Deposition Modelling (FDM). A bridging layer and a continuous basalt fiber pre-impregnated by stiff thermoset epoxy resin are utilized to address the issue of overhanging printing for the upper face sheet. Two kinds of TPMS are employed as the core, as well as two kinds of honeycomb. Multi-step printed samples using a bonding process and counterpart samples without fiber were prepared for the comparison. 3-point bending tests were conducted and a finite element model which can represent the structure characteristic is proposed to investigate the mechanical properties. The results show that the integrated printed sample exhibits better performance in terms of printing quality, flexural modulus, strength and energy absorption (EA) compared with the multi-step printed sample. It has an excellent ability to avoid the catastrophic damage which is usually encountered in the multi-step printed sample due to the introduction of brittle epoxy resin, showing a notable 162.88 % augmentation in specific energy absorption (SEA). The significant improvement lies in that it uses the reinforcement of fiber and the energy absorption capacity of core to full advantage via the strong binding. In addition, as one kind of TPMS, Schwarz Primary structure exhibits the maximum flexural modulus, strength and energy absorption among the four cores. The proposed design and fabrication methodology pave the way for the creation of high-performance sandwich panels with different core structures.

Recyclable bio-based epoxy resin thermoset polymer from wood for circular economy

Due to their extraordinary durability and thermal stability, Epoxy Resin Thermosets (ERTs) are essential in various industries. However, their poor recyclability leads to unacceptable environmental pollution. In this study, Wu et al. successfully synthesized a completely bio-based ERT using lignocellulose-derived building blocks which exhibit outstanding thermal and mechanical properties. Remarkably, these bio-materials degrade via methanolysis without the need of any catalyst, presenting a smart and cost-effective recycling strategy. Furthermore, this approach could be employed for fabricating reusable composites comprising glass fiber and plant fiber, thereby expanding its applications in sustainable transportation, coatings, paints or biomedical devices.

Effect of Methoxy Groups on the Structure–Properties Relationship of Lignin-Derived Recyclable Epoxy Thermosets

Effect of Methoxy Groups on the Structure–Properties Relationship of Lignin-Derived Recyclable Epoxy Thermosets

A dual cross-linking strategy enables fully bio-based epoxy thermosets with superior low dielectric properties and mechanical properties

Bio-based epoxy resins with superior low dielectric properties and mechanical properties is of great significance for sustainable development and environmental protection. Herein, a bio-based active ester curing agent with large free volume was synthesized through a substitution reaction between magnolol and cinnamoyl chloride following by curing epoxidized linseed oil for fully bio-based epoxy thermosets. The curing kinetics of the curing behavior and the curing condition was systematic studied and optimized. The relationship between chemical structure and properties (thermo-mechanical, mechanical, dielectric, and etc.) of the resulting fully bio-based epoxy thermosets was discussed in-depth. The results showed that free radical polymerization and epoxy ring-opening reactions simultaneously occurred in the curing reaction led to a dual cross-linked structure of the resulting fully bio-based epoxy thermosets. The unique structures and the introduction of the rigid benzene groups rendered the tensile strength and the thermal stability of the resulting fully bio-based epoxy thermosets high up to 33.63 MPa and 332.40 °C, respectively. The absence of the secondary hydroxyl groups and the presence of the low polar fatty acid chains in the backbone of the epoxy resins resulted in the dielectric constant and dielectric loss low to 3.19 and 0.012, which was much lower than those of the polymer previously reported. This study provides a simple and facile strategy for the design of environmentally friendly fully bio-based epoxy resins for microelectronics and electronic packaging application.

Chemical and Solvent‐Based Recycling of High‐Performance Epoxy Thermoset Utilizing Imine‐Containing Secondary Amine Hardener

AbstractEpoxy thermosets are indispensable in various industrial applications due to their exceptional material properties. However, their limited recyclability poses a significant challenge for sustainability. To address this issue, integrating recyclable imine moieties into epoxy systems has emerged as a promising strategy. Despite recent advancements, challenges persist concerning the hydrolytic stability of imine‐based epoxy thermosets and the formation of irregular oligomeric structures upon depolymerization. In this study, these shortcomings are solved by designing a liquid imine monomer with secondary amine functionalities, which is subsequently reacted with commercially available epoxy monomers to produce high‐performance epoxy thermosets. Remarkably, the developed imine‐based epoxy system shows no sign of hydrolysis even under high‐temperature aqueous conditions, underscoring its potential for various industrial applications. Only the treatment with aqueous HCl results in the selective formation of exclusively well‐defined molecules, in high isolated yields after depolymerization. Crosslinking these building blocks once again yields recycled polymers with properties identical to pristine material. Moreover, it is discovered that, despite the crosslinked nature of the epoxy thermoset, the complete dissolution of the intact polymer in dichloromethane allowed for simple solvent‐based recycling. Through design on the molecular level, the recycling of imine‐based epoxy polymers is achieved via chemical and solvent‐based techniques.