Cycloaliphatic epoxy resins are known for their synthesis process that eliminates hydrolyzable chlorine, thus avoiding the hydrolysis of hydrolyzable chlorine to hydroxyl groups in conventional epoxies, which is very favorable for the preparation of low dielectric epoxy resins. The curing process using active ester generates no hydroxyl groups, also indicating a promising approach for producing low dielectric epoxy resins. However, the resistance of cycloaliphatic epoxy to nucleophilic reactions restricts it from reacting usually only with anhydrides. This study investigates the reactivity of the active ester with cycloaliphatic epoxy, demonstrating its capability to undergo complete curing reactions at temperatures near 150 C-degrees. Factors influencing this process, including the volatilization of the catalyst DMAP and its reactivity, are examined. Two types of cycloaliphatic epoxies (3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate (EEC) and bis (3,4-epoxycyclohexylmethyl) adipate (BEA)) are combined with an active ester hardener, triacetyl resveratrol (TAR), to prepare epoxy resins. The activation energies for the curing reactions are determined, and the optimal concentration of catalyst 4-dimethylaminopyridine (DMAP) is identified for each resin. The use of catalysts at specific concentrations results in resins with superior mechanical properties (91.7 and 71.4 MPa for EEC/TAR and BEA/TAR), excellent thermal stability (T (d5% )of 354 and 347( degrees)C), and good dielectric properties (dielectric constant of 3.68 and 3.95 at 10 MHz), outperforming anhydride-cured cycloaliphatic epoxy resins. These findings expand the selection of hardeners for cycloaliphatic epoxy resins and highlight the potential of the prepared resins in electronic packaging materials, offering enhanced properties suitable for various applications.

Active ester hardeners are a unique class of epoxy hardeners that undergo a curing reaction without generating secondary hydroxyl groups. This characteristic enables the production of low dielectric and low moisture absorption epoxy resins. In this study, two active ester hardeners, bisphenol A diisobutyrate (DIB) and bisphenol A dimethacrylate (DMA), were used to prepare epoxy resins by reacting with a resveratrol-based epoxy monomer (REP). By cross-linking the double bonds in the resin (using dicumyl peroxide, DCP), the properties of the resin can be dramatically changed. Among the resins prepared, REP/DMA/DCP exhibited the highest cross-linking density, approximately 48 times that of REP/DIB. Its storage modulus at 300 ˚C remained at 600 MPa, indicating an equivalent glass transition temperature (Tg) higher than 300 ˚C. Additionally, the cross-linking of the ester side groups increased the initial degradation temperature by 12-13 ˚C, reaching 395-396 ˚C. Regarding the coefficient of thermal expansion (CTE), the cross-linking of ester side groups had no significant effect on the CTE in the glassy state. However, it drastically reduced the CTE above the glass transition temperature. The average CTE (30-300 ˚C) of REP/DMA/DCP was only 106 ppm/˚C. Furthermore, the cross-linking of the ester side groups appeared to reduce the dielectric constant but increased the dielectric loss and the water absorption rate. Nevertheless, REP/DMA/DCP's dielectric constant at 10 MHz of 3.07, dielectric loss of 0.01, and saturated water absorption of 0.77 wt% remain in the low range.

In order to address the relative brittleness and non-recyclability defects of traditional cross-linked epoxy resins, a novel self-healing and reprocessable epoxy resin based on dynamic piperazine-hindered urea bonds (PA-HUBs) was synthesized. Piperazine is a cheap cyclic diamine, which can regulate the skeleton stiffness of epoxy network and control the mechanical properties of epoxy materials. The tensile strength of cured epoxy resin reaches 103 MPa. In addition, the piperazine monomer contains two methyl substituents and an asymmetric aliphatic ring structure, which provides sufficient chain mobility to activate dynamic exchange reactions, and imparts highly dynamic properties to the conventional urea bond, allowing the urea bonds to possess both stability and dynamic properties. Consequently, the synthesized epoxy resin exhibits not only the excellent mechanical performance but also the remarkable self-healing, reprocessable, shape memory and shape reconfiguration capabilities. The epoxy samples with scratches can basically achieve self-healing within 10 min, and the mechanical properties recovery rate of welded splines is as high as 80 %. Furthermore, we also regulated the content of dynamic PAHUBs and the cross-linking density of the resin network to examine their impact on the dynamic properties and mechanical performance. Further analysis showed that the higher dynamic bond content and lower cross-linking density increase the free volume of dynamic bond exchange and the stress relaxation rate, which further improves the exchange efficiency of dynamic bonds and endows the resin with better self-healing ability. This kind of piperazine-hindered urea bond, which is dynamically adjustable and has both mechanical stability and dynamic properties, introduces a novel approach for solving the balance problem between the mechanical and dynamic performance of thermosets and preparing dynamic polymer materials with excellent performance.

During recent decades, intrinsic self-healable thermosetting materials by integrating dynamic covalent bonds (DCBs) have been widely used. In this study, through the molecular structure design, a flexible polyurethane curing agent based on hindered urea bonds (HUBs) was successfully prepared by the reaction of Hexamethylene diisocyanate trimer (THDI) and sterically hindered secondary amine, which was further used as a curing agent to cure epoxy resin. Therefore, a new type of epoxy thermosetting material (TBEP) with dynamic hindered urea bond was synthesized and the preparation and performance of TBEP were confirmed and characterized by infrared spectroscopy, thermomechanical analysis and thermal stability test. The results show that the HUBs are successfully integrated into the epoxy resin and endow the epoxy thermosets with brilliant self-healable, reprocessable, recyclable and shape memory properties. Simultaneously, the existence of flexible polyurethane chain in the crosslinking network effectively solves the brittleness problem of epoxy resin, promotes the mechanical performance of epoxy thermosets, and further broadens the its application field. This work provides a simple and efficient method to design flexible and self-healable epoxy thermosets with brilliant mechanical performance, which solves the contradiction between outstanding mechanical properties and self-healing ability of epoxy resin to some extent, and is environmentally friendly and cost-effective in acquisition and application.

A composite was prepared by in-situ polymerization of liquid crystal epoxy (LCE4) with a low dielectric and high thermal conductivity boron nitride (BN) filler, which the filler (f-BN) was surface-functionalized by gamma-glycidoxypropyltrimethoxysilane (KH560) and aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS). The surface-functionalized BN was more uniformly dispersed in LCE4, which improved the interfacial compatibility between inorganic and organic phases. Compared with pure LCE4, KH560, and NH2-POSS modified f-BN/LCE4 composites exhibited a higher glass transition temperature, better thermal stability, and higher thermal conductivity. For example, when the f-BN content reached 30 wt%, the energy storage modulus of the composite increased to 2580 MPa, and the glass transition temperature was 103?. The thermal conductivity of this 30 wt% f-BN composite was 0.48 W m(-1) K-1, 128.6% higher than that of pure LCE4. In addition, thermal stability, low hygroscopicity, and dielectric properties of the composites were characterized and analyzed to explore the application prospects of f-BN/LCE4 composites in electronic packaging and in high-performance microelectronic devices.

Vitrimers are polymers possessing a covalent adaptable network (CANs) that can undergo a topological structural transformation under specific conditions, enabling material reprocessing. In this study, an active ester hardener containing imine bonds (TAI) was synthesized, and subsequently, epoxy resin with CANs (epoxy vitrimer, DGEBA/TAI) was prepared, which exhibited excellent thermal stability (initial degradation temperature of 364 degrees C and char yield at 800 degrees C of 30%), low water absorption (0.25 wt %), and good dielectric properties (dielectric constant of 3.37 and dielectric loss of 0.013). A comparative scratch healing test between the epoxy vitrimer and conventional epoxy resin showed that the hard vitrimer could not demonstrate self-healing ability and that scratch healing was derived from deformation recovery. The performance of such hard vitrimers should focus on recycling and reprocessing rather than a self-healing capability. Thus, the resin could be effectively recycled and reused by a hot pressing or solvent method, resulting in recycled resins with good tensile strength (70 MPa for hot-press welding and 58 MPa for solvent recycling) compared to the originals (69 MPa). In addition, the vitrimer materials allow shape reconfiguration through a network structure transformation, and an alternative analytical method was proposed to obtain the relaxation time of the vitrimer by fitting the equation of the stress relaxation curve, which could mitigate some of the interferences and provide a method for data reliability verification of the viscoelastic properties of the vitrimer.

In this work, two resveratrol-derived epoxy thermosets (REP/TAR and REP/TTR) were prepared, and their cross-linked structure and thermal degradation were analyzed.

Thermally conductive pressure-sensitive adhesive (PSA) has received a great amount of attention in recent years, but the traditional PSA hardly loses adhesion properties after UV irradiation or heating. Therefore, endowing thermally conductive adhesive with UV-responsive peelability becomes a design strategy. Herein, vinyl-functionalized graphene (AA-GMA-G) is prepared by modifying graphene with acrylic acid and subsequently reacting with glycidyl methacrylate. Then, the UV-curable acrylate copolymer is synthesized by grafting glycidyl methacrylate. Finally, the novel thermally conductivity PSA with UV-responsive peelability is obtained by blending the copolymer with AA-GMA-G and photoinitiator. The results show that the PSA at 2 wt% AA-GMA-G loading exhibits an excellent thermal conductivity (0.74 W m-1 K-1 ) and a relatively strong peel strength, increasing by 15% compared with pristine graphene/PSA. Interestingly, the peel strength of AA-GMA-G/PSA can achieve a dramatic drop after UV treatment, and the decrease rate is 96.7%. Therefore, the novel thermally conductive PSA with UV-responsive peelability has potential applications in certain electronic devices.

Polymethyl methacrylate (PMMA) is widely used, but its polymerization process is highly hazardous and the relevant thermal hazards have not been adequately investigated. Herein, the thermal safety and kinetic mechanisms of methyl methacrylate (MMA) polymerization are explored. The effect of monomer concentration on the exothermic characteristics is first investigated using a reaction calorimeter. The results indicate that the exothermic behavior of this reaction is significantly influenced by the monomer concentration. Meanwhile, a quantitative relationship between the specific enthalpy and monomer concentration is determined. Moreover, overall rate expression is developed by a rapid quantitative method to further elucidate the quantitative dependence of reaction rate on the process conditions. Subsequently, adiabatic experiment is performed to reveal the thermal controllability of this reaction. Finally, risk level is ascertained to propose constructive countermeasures. This work provides guidance for the safe operation of MMA polymerization, and the methodology also furnishes universal solutions for analogous reactions.

Given the fossil fuel energy crisis and serious environmental pollution in recent years, one way to alleviate the problem is to introduce dynamic covalent chemistry into thermosetting resins to give the material processable and recyclable properties, creating a new type of eco-friendly material. Hindered urea bonds can undergo reversible exchange reactions at high temperatures to decompose into amine and isocyanate. This reversible addition reaction is currently a prominent research focus in the development of reprocessable thermosets. In this work, we synthesize a novel curing agent with hindered urea bonds without any catalysts. Then characterize the resulting epoxy vitrimers based on hindered urea bond (HUG-EP) using FT-IR and 1H NMR, confirming the successful introduction of hindered urea bonds into the epoxy resin. A variety of tests are carried out, such as those to assess thermal stability, swelling, shape-memory, re-processability and tensile strength. The results demonstrate that HUG-EP can rapidly self-healed within 20 min at 160 degrees C, with the tensile strength was maintained at 87.15 % of the original during the welding experiments. Furthermore, it can also be reprocessed by hot-pressing several times at 160 degrees C. Thus, the introduction of hindered urea bonds into the crosslinked network proves to be an effective and practicable approach for producing thermosetting resins with reprocessing, self-healing, and shape memory capabilities.

Traditional epoxy thermosets have been extensively used in many fields, including the field of carbon fiber composite materials, which is favored by a large number of researchers. But they usually cannot be recycled under mild conditions. To make matters worse, the material loses its usefulness once it is damaged. Self-healing and degradable thermosetting resins with dynamic covalent bonds offer a potential solution to this conflict. In this paper, a series of epoxy polymers named EPCN based on dynamic imine bonds were easily prepared by a one -pot method using inexpensive industrial materials terephthalaldehyde and common bisphenol A diglycidyl ether as raw materials, which were cured by D230. The results show that the materials exhibit certain self-healing, reprocessability and thermadapt shape memory properties due to the dynamic properties of the imine bonds. Moreover, EPCN epoxy polymers can be degraded due to the hydrolysis of dynamic imine bonds, and their degradation exhibit temperature and acidity dependence. More importantly, the recyclable carbon fiber rein-forced polymer composites prepared with EPCN-4 as the resin matrix can be completely degraded under weak acid conditions, leading to the ready and non-destructive recycling of its carbon fiber composite. We envision this reprocessable and degradable carbon fiber-reinforced composite material with cheap raw materials, simple process, and suitable for mass production will make it a potential candidate for sustainable structural material applications.

As reported herein, a novel addition-type liquid silicone rubber (LSR)/red mud (RM) composite has been synthesized. Triethoxyvinylsilane (KH151) was used as a surface modification agent to treat RM and form hydrophobic surfaces. The optimal formulation of the composite was determined by the mechanical properties of the LSR that were prepared at different crosslinker and filler contents. The reinforcement mechanism of modified RM on LSR was revealed by combining Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy and mechanical property tests. Thermal degradation behavior of RM/LSR at elevated temperature was investigated by the thermogravimetric analysis (TG), TG-FTIR and alteration of mechanical properties after thermal aging. The results of the experiment indicate that modified RM increased the tensile strength and Young's modulus of LSR dramatically and provides superior thermal stability to the LSR. With 100 phr RM added, the tensile strength of RM/LSR composite was almost 12 times greater than that of pure LSR, and pure LSR degrades completely after aging at 300? for 24 h while RM/LSR retains its mechanical properties.

In this paper, a series of small monomers were synthesized to explore the dynamic reversible properties of phenol-carbamate bonds (PCBs), and the bimolecular exchange mechanism of PCBs was verified. Based on this mechanism, a novel thermo-healing recyclable epoxy resin with high mechanical performance and shape memory function was successfully developed. Meanwhile, the number of reversible phenol-carbamate bonds in this system was increased by molecular structure design, which increased the chance of reversible cleavage and recombination of the dynamic covalent bonds. Compared with our previous work, the thermo-healing efficiency of the epoxy thermosets was greatly increased, and the target polymer achieved an excellent balance between high thermo-healing efficiency and good mechanical performance. Further post-treatment experiments show that the cured epoxy resin can also be well recycled by solvent degradation or hot-pressing process. What's more, a novel carbon fiber (CF) reinforced polymer composite material was synthesized by taking that prepared epoxy thermoset as a matrix, which greatly improve the mechanical properties of epoxy resin, and the CF cloths can be recycled when the epoxy resin is removed by chemical degradation. In addition, due to the existence of reversible crystallizable switching segments in the epoxy resin system, when the temperature is above its Tg, it can be triggered by thermal energy, so that the film can rapidly recover from the temporary shape to the permanent shape. This study also provides a new direction for the development of novel multifunctional intelligent polymers.

Developing self-healable, recyclable and reprocessable polymer materials is one of the effective ways to relieve plastic pollution and save resources. Using dynamic reversible hindered urea bonds (HUBs) to construct self-healing materials have become a hot topic to investigate renewable materials. HUBs have a large substituent on its nitrogen atom, which can be dynamically dissociated into related amines and isocyanates without the need for catalysts. Here, integrating HUBs into the epoxy cross-linking network would obtain dynamic covalent self-healing epoxy resin based on large hindered urea bonds (HUBs-EP), which could endow the crosslinked networks with fast reconfigurability under relatively low temperature. In this work, HUBs-EP has optional recyclability (In N, N-dimethylformamide and tetrahydrofuran), good reprocessability (under simple hot-pressing procedure) and rapid self-healing property under 110 degrees C within 10 min all due to reversible dissociation and recombination of dynamic covalent urea bonds. The extremely simple manufacturing method of dynamically reversible polymers obtained by integrating dynamic covalent bonds into thermoset will give a major hint for the development of sustainable materials.

In recent years, the reversible addition reaction of isocyanates and active hydrogen compounds has aroused wide concern. The synthesis of a novel dynamic covalent system based on phenol-carbamate bonds (PCBs) and its application in the preparation of thermo-healing and recycled epoxy resins have become a research hotspot. Herein, a compound with a phenolic hydroxyl group was designed and synthesized, which was used to react with isocyanate to obtain the dynamic covalent system of PCBs. Based on PCBs, a cross-linked polyurethane curing agent and the epoxy thermosetting resin with recyclability and thermo-healing ability were prepared. Differ-ential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), stress relaxation analysis and tensile test were carried out on the synthesized epoxy resins based on PCBs (PCBs-EP). The results showed that the dynamic PCBs endow epoxy thermosets with outstanding reprocessability, thermo-healing, welding, recycling and shape memory properties. Based on the reversible dynamic phenol-carbamate bonds, PCBs-EP can be thermally healed within 2 h under 100 degrees C, and the thermo-healing effect is obvious. More surprisingly, the tensile strength of PCBs-EP reaches 95.89 (+/- 1.06) MPa, and its tensile strength still maintains 74.13% of the original after healed and 70.6% of the original after welded. Therefore, the stra-tegies for incorporating dynamic covalent PCBs into thermosetting epoxy resins provide a feasible strategy for preparing cross-linked epoxy thermosets with high thermo-healing efficiency and high mechanical strength in a cost-effective manner.

Thermal interface materials (TIMs) used to fill the gaps between chip and heat sink are one of the most important materials for electronic packaging. Low thermal resistance is the key to achieving high heat dissipation efficiency. However, most studies only focused on how to enhance the thermal conductivity of the gel TIMs and ignored the thermal resistance, which is significantly influenced by the rheological properties. In this work, we aimed to investigate the effects of in situ modification of aluminum fillers on the rheological properties and thermal resistance of the gel TIMs. Six modifiers were compared for their ability to improve the compatibility between aluminum fillers and silicone oil. The rheological results showed that the gel TIM modified with 0.170 wt% dodecyl trimethoxysilane had the best rheological properties, including the lowest viscosity and yield stress, the weakest Payne effect, and the shortest relaxation time. The thermal resistance measurements further verified that the bond line thickness and thermal resistance of gel TIMs were determined by the rheological properties. This work provides a reference for the formulation design and process optimization of gel TIMs.

The fabrication and development of excellent thermoset polymers with self-healing and shape memory properties is highly desirable. Herein, a novel high-strength epoxy resin (EP-SeSe) with diselenide bonds was rationally designed for rapid repair materials in building constructions and electrical packaging. The resultant resins exhibit excellent shape memory performance and self-healing performance due to the dynamic diselenide bonds (SeSe), while maintaining a high mechanical strength (tensile strength = 105 MPa and E = 2.0GPa), and exceptional thermal stability. It is especially noteworthy that the diselenide bonds of the bis(4-aminophenyl) diselenide (BAPDSe) allow EP-SeSe to exchange molecular chains in a dynamic manner, facilitating transport of chain segments while the ortho-phenyl groups prevent the side effects of weak bonds on mechanical properties. Furthermore, when the temperature exceeds Tg, EP-SeSe displays fast stress relaxation, self-healing, remodeling, and weldability due to the [2 + 1] radical-mediated mechanism of the diselenide bonds. We envision that this study provides a facile method for constructing robust multifunctional epoxy resins, which have great potential applications for self-healing and shape-memory epoxy resins.

Epoxy resins are widely used for electronic packaging materials due to their good performance. A common way to cure epoxy is to add anhydride as a hardener, to this, we added a less used curing method, catalytic curing, to study their effect on the curing system and curd samples. Polymers containing naphthalene rings usually have low moisture absorption, good thermal stability, dimensional stability, and dielectric properties. Here, we used two naphthalene epoxy monomers (1,6-naphthalene diglycidyl ether (1,6-NDE) and 2,7-NDE) and cured them with two methods (anhydride (methyl nadic anhydride, MNA) / accelerator (Tris(dimethylaminomethyl)phenol, DMP-30) curing system and catalyst (DMP-30) curing system). We obtained four types of epoxy resins and compared the differences in their structure and performance. All epoxy resins had excellent tensile properties at around 100 MPa tensile strength. Catalyst cured resins had better thermal stability and higher glass transition temperature that close to 180C (Tg-DMA), compared with anhydride cured resins. Meanwhile, 1,6-naphthalene epoxy resins had better performance than 2,7-naphthalene epoxy resins in high glass transition temperature and high crosslink density. Overall, all naphthalene epoxy resins had good performances, and catalyst-cured resins performed better and provided an additional method. Herein, these types of naphthalene epoxy resins have potential applications in the field of electronic packaging.

Polymer composites have been widely employed as electronic packaging materials, due to their low cost, flexibility, chemical stability, and high malleability, etc. However, the thermal conductivity of polymer composites becomes increasingly requirement, with the rapid growth of electronics toward miniaturization and high-power density. Conventional method to enhance the thermal conductivity of polymer is addition of high-content thermally conductive fillers, but it will deteriorate other significant properties of polymers, such as optical, electrical, and mechanical performance. Herein, we report an ice-templated assembly strategy to construct threedimensional thermally conductive networks of BN nanosheets (BNNS) and silver nanowires (AgNWs) in epoxy resin composites. The thermal-conduction pathway can be easily built by the synergistic effects between twodimensional BNNS and one-dimensional AgNW. Furthermore, the welding of the adjacent AgNWs through low-temperature sintering process enlarges the total contact area per unit filler volume. The resulted polymer composite thus exhibits a through-plane thermal conductivity of 1.10 Wm(-1)K(-1) at only about 5.0 vol% fillers content, which is six times higher than that of the pure epoxy resin. This work shows great potential in advanced packaging materials, such as substrate materials and printed circuit board materials.