Design of Co-Cured Multi-Component Thermosets with Enhanced Heat Resistance, Toughness, and Processability via a Machine Learning Approach.

Designing heat-resistant thermosets with excellent comprehensive performance has been a long-standing challenge. Co-curing of various high-performance thermosets is an effective strategy, however, the traditional trial-and-error experiments have long research cycles for discovering new materials. Herein, a two-step machine learning (ML) assisted approach is proposed to design heat-resistant co-cured resins composed of polyimide (PI) and silicon-containing arylacetylene (PSA), that is, poly(silicon-alkyne imide) (PSI). First, two ML prediction models are established to evaluate the processability of PIs and their compatibility with PSA. Then, another two ML models are developed to predict the thermal decomposition temperature and flexural strength of the co-cured PSI resins. The optimal molecular structures and compositions of PSI resins are high-throughput screened. The screened PSI resins are experimentally verified to exhibit enhanced heat resistance, toughness, and processability. The research framework established in this work can be generalized to the rational design of other advanced multi-component polymeric materials.

Mitochondrial Fission Is Involved in Heat Resistance in Zebrafish.

Global warming and extreme weather events pose a significant threat to global biodiversity, with rising water temperatures exerting a profound influence on fish conservation and fishery development. In this study, we used zebrafish as a model organism to explore the impact of a heat acclimation period on their survival rates. The results demonstrated that a 2-month heat acclimation period almost completely mitigated heat stress-induced mortality in zebrafish. Subsequent analysis of the surviving zebrafish revealed a predominance of hepatic mitochondria in a fission state. Remarkably, a short-term fasting regimen, which induced hepatic mitochondrial fission, mirrored the outcomes of the protective effect of heat acclimation and augmented animal survival under heat stress. Conversely, treatment with a mitochondrial fission inhibitor within the fasting group attenuated the elevated survival rate. Furthermore, zebrafish embryos subjected to brief heat acclimation also exhibited increased heat resistance, a trait diminished by a chemical intervention inhibiting mitochondrial fission. This suggests a shared mechanism for heat resistance between embryos and adult zebrafish. These findings underscore the potential use of inducing mitochondrial fission to enhance heat resistance in zebrafish, offering promise for fish biodiversity conservation in the face of global warming.

Microwave De-Icing Efficiency Improvement of Asphalt Mixture with Structural Layer Optimization and Heat-Resistance Design.

The application of microwave de-icing technology in road engineering is constrained by its low energy utilization rate, which can be attributed to low heat production rates and ineffective heat dissipation to the underlying pavement. In this work, asphalt mixtures are designed as an upper layer (heating layer) and a lower layer (thermal-resistance layer). Magnetite slag was selected as a microwave-sensitive source for generating heat, and expanded perlite powder was incorporated into the lower layer as a thermal resistance material. Structural layer optimization and thermal-resistance layer design of the asphalt mixture were carried out by changing the thickness of the upper and lower layers to further improve the heat production rates. The design effectiveness is comprehensively evaluated by factors such as the changing law of the average surface temperature of mixtures, ice-melting time, and cost-effectiveness analyses. The results show that EP possesses better thermal stability, lower microwave energy conversion ability and more excellent heat-resistance potential compared with mineral powder. The heat-resistance layer with EP can prevent heat from being conducted to the lower layer and promote it to concentrate on the specimen surface, which can endow the microwave heating efficiency of specimens to be further improved by up to 26.97% and the de-icing time reduced by 10%, ascribed to the heat-resistance design. Furthermore, the collaborative design of the structural layer optimization and heat-resistance layer can increase energy utilization efficiency and save microwave-absorbing materials while ensuring excellent microwave de-icing efficiency.

Controlled Structural Relaxation of Aramid Nanofibers for Superstretchable Polymer Fibers with High Toughness and Heat Resistance.

Polymer fibers that combine high toughness and heat resistance are hard to achieve, which, however, hold tremendous promise in demanding applications such as aerospace and military. This prohibitive design task exists due to the opposing property dependencies on chain dynamics because traditional heat-resistant materials with rigid molecular structures typically lack the mechanism of energy dissipation. Aramid nanofibers have received great attention as high-performance nanoscale building units due to their intriguing mechanical and thermal properties, but their distinct structural features are yet to be fully captured. We show that aramid nanofibers form nanoscale crimps during the removal of water, which primarily resides at the defect planes of pleated sheets, where the folding can occur. The precise control of such a structural relaxation can be realized by exerting axial loadings on hydrogel fibers, which allows the emergence of aramid fibers with varying angles of crimps. These crimped fibers integrate high toughness with heat resistance, thanks to the extensible nature of nanoscale crimps with rigid molecular structures of poly(p-phenylene terephthalamide), promising as a template for stable stretchable electronics. The tensile strength/modulus (392-944 MPa/11-29 GPa), stretchability (25-163%), and toughness (154-445 MJ/cm3) are achieved according to the degree of crimping. Intriguingly, a toughness of around 430 MJ/m3 can be maintained after calcination below the relaxation temperature (259 °C) for 50 h. Even after calcination at 300 °C for 10 h, a toughness of 310 MJ/m3 is kept, outperforming existing polymer materials. Our multiscale design strategy based on water-bearing aramid nanofibers provides a potent pathway for tackling the challenge for achieving conflicting property combinations.

Thermally Stable and Transparent Polyimide Derived from Side-Group-Regulated Spirobifluorene Unit for Substrate Application.

Advancements in flexible electronic technology, especially the progress in foldable displays and under-display cameras (UDC), have created an urgent demand for high-performance colorless polyimide (CPI). However, current CPIs lack sufficient heat resistance for substrate applications. In this work, four kinds of rigid spirobifluorene diamines are designed, and the corresponding polyimides are prepared by their condensation with 5,5'-(perfluoropropane-2,2-diyl) bis(isobenzofuran-1,3-dione) (6FDA) or 9,9-bis(3,4-dicarboxyphenyl) fluorene dianhydride (BPAF). The rigid and conjugated spirobifluorene units endow the polyimides with higher glass transition temperature (Tg) ranging from 356 to 468 °C. Their optical properties are regulated by small side groups and spirobifluorene structure with a periodically twisted molecular conformation. Consequently, a series of CPIs with an average transmittance ranging from 75% to 88% and a yellowness index (YI) as low as 2.48 are obtained. Among these, 27SPFTFA-BPAF presents excellent comprehensive performance, with a Tg of 422 °C, a 5 wt.% loss temperature (Td5) of 562 °C, a YI of 3.53, and a tensile strength (δmax) of 140 MPa, respectively. The mechanism underlying the structure-property relationship is investigated by experimental comparison and theoretical calculation, and the proposed method provides a pathway for designing highly rigid conjugated CPIs with excellent thermal stability and transparency for photoelectric engineering.

Differential impacts of nonsteroidal anti-inflammatory drugs on lifespan and healthspan in aged Caenorhabditis elegans.

Aging and age-related diseases are intricately associated with oxidative stress and inflammation. Nonsteroidal anti-inflammatory drugs (NSAIDs) have shown their promise in mitigating age-related conditions and potentially extending lifespan in various model organisms. However, the efficacy of NSAIDs in older individuals may be influenced by age-related changes in drug metabolism and tolerance, which could result in age-dependent toxicities. This study aimed to evaluate the potential risks of toxicities associated with commonly used NSAIDs (aspirin, ibuprofen, acetaminophen, and indomethacin) on lifespan, healthspan, and oxidative stress levels in both young and old Caenorhabditis elegans. The results revealed that aspirin and ibuprofen were able to extend lifespan in both young and old worms by suppressing ROS generation and enhancing the expression of antioxidant SOD genes. In contrast, acetaminophen and indomeacin accelerated aging process in old worms, leading to oxidative stress damage and reduced resistance to heat stress through the pmk-1/skn-1 pathway. Notably, the harmful effects of acetaminophen and indomeacin were mitigated when pmk-1 was knocked out in the pmk-1(km25) strain. These results underscore the potential lack of benefit from acetaminophen and indomeacin in elderly individuals due to their increased susceptibility to toxicity. Further research is essential to elucidate the underlying mechanisms driving these age-dependent responses and to evaluate the potential risks associated with NSAID use in the elderly population.

Metal-organic framework adhesives with exceptionally high heat resistance.

We synthesized high-heat-resistant adhesives based on metal - organic frameworks owing to their high decomposition temperature and the absence of a glass transition. Heat-resistance tests were performed on adhesive joints consisting of zeolitic imidazolate framework (ZIF)-67-based adhesives and a copper substrate. The as-synthesized ZIF-67-based adhesive exhibited heat resistances at 600 and 700°C in air and nitrogen atmospheres, respectively, comparable to those of conventional high-heat-resistant polymer-based adhesives. The degradation mechanism of the ZIF-67 adhesives was investigated, and their high heat resistance was attributed to the stable existence of the ZIF-67 qtz phase in the adhesive layer at high temperatures without the formation of voids. Thus, adhesives based on ZIF-67 and other metal - organic frameworks can be applied in high-temperature industrial systems.

By focusing on its high thermal stability and absence of glass transition, the ZIF-67 gel was found to have high potential that is comparable to existing heat-resistant adhesives.

Ultrahigh Heat/Fire-Resistant, Mechanically Robust, and Closed-Loop Chemical Recyclable Polycarbonate Enabled by Facile Bond Dissociation Energy Modulation.

Plastics serve as an essential foundation in contemporary society. Nevertheless, meeting the rigorous performance demands in advanced applications and addressing their end-of-life disposal are two critical challenges that persist. Here, an innovative and facile method is introduced for the design and scalable production of polycarbonate, a key engineering plastic, simultaneously achieving high performance and closed-loop chemical recyclability. The bisphenol framework of polycarbonate is strategically adjusted from the low-bond-dissociation-energy bisphenol A to high-bond-dissociation-energy 4,4'-dihydroxydiphenyl, in combination with the incorporation of polysiloxane segments. As expected, the enhanced bond dissociation energy endows the polycarbonate with an extremely high glow-wire flammability index surpassing 1025 °C, a 0.8 mm UL-94 V-0 rating, a high LOI value of 39.2%, and more than 50% reduction of heat and smoke release. Furthermore, the π-π stacking interactions within biphenyl structures resulted in a significant enhancement of mechanical strength by as more as 37.7%, and also played a positive role in achieving a lower dielectric constant. Significantly, the copolymer exhibited outstanding closed-loop chemical recyclability, allowing for facile depolymerization into bisphenol monomers and the repolymerized copolymer retains its high heat and fire resistance. This work provides a novel insight in the design of high-performance and closed-loop chemical recyclable polymeric materials.

Progress in using cross-linking technologies to increase the thermal stability of colloidal delivery systems.

In recent years, crosslinking technology has been found and widely used in food, textile, pharmaceutical, bioengineering and other fields. Crosslinking is a reaction in which two or more molecules bond to each other to form a stable three-dimensional network structure to improve the strength, heat resistance and other properties of substances. The researchers found that the cross-linking technology has a significant effect on improving the thermal stability of the colloidal delivery system. In this paper, crosslinking techniques that can be used to improve the thermal stability of colloidal delivery systems are reviewed, including enzyme-, ion-, chemical-, and combined cross-linking. Initially, the underlying mechanisms of these crosslinking technologies is reviewed. Then, the impacts of crosslinking on the heat-stability of colloidal delivery systems are discussed. Finally, the application of crosslinked delivery systems in improving the thermal stability of probiotics, polyphenols, pigments, and nutrients in foods and food packaging materials is introduced. The ability of proteins and polysaccharides to form heat-stable colloidal delivery systems can be improved by crosslinking. Nevertheless, more research is required to establish the impact of different crosslinking on the thermal stability of a broader range of different delivery systems, as well as to ensure their safety and efficacy.

Resistance of an intertidal oyster(Saccostrea mordax)to marine heatwaves and the implication for reef building.

Marine heatwaves (MHWs) have a significant impact on intertidal bivalves and the ecosystems they sustain, causing the destruction of organisms' original habitats. Saccostrea mordax mainly inhabits the intertidal zone around the equator, exhibiting potential tolerance to high temperatures and maybe a species suitable for habitat restoration. However, an understanding about the tolerance mechanism of S. mordax to high temperatures is unclear. It is also unknown the extent to which S. mordax can tolerate repeated heatwaves of increasing intensity and frequency. Here, we simulated the effects of two scenarios of MHWs and measured the physiological and biochemical responses and gene expression spectrum of S. mordax. The predicted responses varied greatly across heatwaves, and no heatwave had a significant impact on the survival of S. mordax. Specifically, there were no statistically significant changes apparent in the standard metabolic rate and the activities of enzymes of the oyster during repeated heatwaves. S. mordax exposed to high-intensity heatwaves enhanced their standard metabolic rate to fuel essential physiological maintenance and increasing activity of SOD and expression of HSP70/90. These strategies are presumably at the expense of functions related to immunity and growth, as best exemplified by significant depressions in activities of enzymes (NaK, CaMg, T-ATP, and AKP) and expression levels of genes (Rab, eEF-2, HMGR, Rac1, SGK, Rab8, etc.). The performance status of S. mordax tends to improve by implementing a suite of less energy-costly compensatory mechanisms at various levels of biological organization when re-exposed to heatwaves. The adaptive abilities shown by S. mordax indicate that they can play a crucial role in the restoration of oyster reefs in tropical seas.

Double Perovskite Single Crystals with High Laser Irradiation Stability for Solid-State Laser Lighting and Anti-counterfeiting.

Laser lighting devices, comprising an ultraviolet (UV) laser chip and a phosphor material, have emerged as a highly efficient approach for generating high-brightness light sources. However, the high power density of laser excitation may exacerbate thermal quenching in conventional polycrystalline or amorphous phosphors, leading to luminous saturation and the eventual failure of the device. Here, for the first time, we raise a single-crystal (SCs) material for laser lighting considering the absence of grain boundaries that scatter electrons and phonons, achieving high thermal conductivity (0.81 W m-1 K-1) and heat-resistance (575 °C). The SCs products exhibit a high photoluminescence quantum yield (89%) as well as excellent stability toward high-power lasers (>12.41 kW/cm2), superior to all previously reported amorphous or polycrystalline matrices. Finally, the laser lighting device was fabricated by assembling the SC with a UV laser chip (50 mW), and the device can maintain its performance even after continuous operation for 4 h. Double perovskite single crystals doped with Yb3+/Er3+ demonstrated multimodal luminescence with the irradiation of 355 and 980 nm lasers, respectively. This characteristic holds significant promise for applications in spectrally tunable laser lighting and multimodal anticounterfeiting.

Involvement of ROS and calcium ions in developing heat resistance and inducing antioxidant system of wheat seedlings under melatonin's effects.

The stress-protective effect of melatonin (N-acetyl-5-methoxytryptamine) on plant cells is mediated by key signaling mediators, in particular calcium ions and reactive oxygen species (ROS). However, the links between changes in calcium and redox homeostasis and the formation of adaptive responses of cultivated cereals (including wheat) to the action of high temperatures have not yet been studied. In the present study, we investigated the possible involvement of ROS and calcium ions as signaling mediators in developing heat resistance in wheat (Triticum aestivum L.) seedlings and activating their antioxidant system. Treatment of 3-day-old etiolated seedlings with melatonin solutions at concentrations 0.01-10 µM increased their survival after exposure to 45 °C for 10 min. The most significant stress-protective effect was exerted by melatonin treatment at 1 µM concentration. Under the influence of melatonin, a transient enhancement of superoxide anion radical (O2•-) generation and an increase in hydrogen peroxide content were observed in roots, with a maximum at 1 h. Four hours after treatment with melatonin, the activity of catalase and guaiacol peroxidase increased in roots, while the activity of superoxide dismutase did not change significantly. After exposure to 45 °C, the activity of catalase and guaiacol peroxidase was higher in the roots of melatonin-treated wheat seedlings, and the indices of ROS generation, content of the lipid peroxidation product malonic dialdehyde, and cell membrane damage were lower than in control seedlings. Melatonin-induced changes in root ROS generation and antioxidant enzyme activities were eliminated by pretreatment with the hydrogen peroxide scavenger dimethylthiourea (DMTU), NADPH oxidase inhibitor imidazole, and calcium antagonists (the extracellular calcium chelator EGTA and phospholipase C inhibitor neomycin). Treatment with DMTU, imidazole, EGTA, and neomycin also abolished the melatonin-induced increase in survival of wheat seedlings after heat stress. The role of calcium ions and ROS, generated with the participation of NADPH oxidase, as signaling mediators in the melatonin-induced antioxidant system and heat stress resistance of wheat seedlings have been demonstrated.

Phenotypic, genotypic, and resistome of mesophilic spore-forming bacteria isolated from pasteurized liquid whole egg.

The production of whole-liquid eggs is of significant economic and nutritional importance. This study aimed to assess the phenotypic and genotypic diversity of mesophilic aerobic spore-forming bacteria (n = 200) isolated from pasteurized whole liquid egg and liquid egg yolk. The majority of the isolates were identified as belonging to the genera Bacillus (86 %), followed by Brevibacillus (10 %) and Lysinibacillus (4 %). For the phenotypic characterization, isolates were subjected to various heat shocks, with the most significant reductions observed at 80 °C/30 min and 90 °C/10 min for isolates recovered from raw materials. On the other hand, the decrease was similar for isolates recovered from raw material and final product at 100 °C/5 min and 110 °C/5 min. Genotypic genes related to heat resistance (cdnL, spoVAD, dacB, clpC, dnaK, and yitF/Tn1546) were examined for genotypic characterization. The dnaK gene showed a positive correlation with the highest thermal condition tested (110 °C/5 min), while 100 °C/5 min had the highest number of positively correlated genes (clpC, cdnL, yitF/Tn1546, and spoVAD). Whole Genome Sequencing of four strains revealed genes related to sporulation, structure formation, initiation and regulation, stress response, and DNA repair in vegetative cells. The findings of this study indicate that these mesophilic aerobic spore-forming bacteria may adopt several strategies to persist through the process and reach the final product. As the inactivation of these microorganisms during egg processing is challenging, preventing raw materials contamination and their establishment in processing premises must be reinforced.

The Listeria monocytogenes persistence factor ClpL is a potent stand-alone disaggregase.

Heat stress can cause cell death by triggering the aggregation of essential proteins. In bacteria, aggregated proteins are rescued by the canonical Hsp70/AAA+ (ClpB) bi-chaperone disaggregase. Man-made, severe stress conditions applied during, e.g., food processing represent a novel threat for bacteria by exceeding the capacity of the Hsp70/ClpB system. Here, we report on the potent autonomous AAA+ disaggregase ClpL from Listeria monocytogenes that provides enhanced heat resistance to the food-borne pathogen enabling persistence in adverse environments. ClpL shows increased thermal stability and enhanced disaggregation power compared to Hsp70/ClpB, enabling it to withstand severe heat stress and to solubilize tight aggregates. ClpL binds to protein aggregates via aromatic residues present in its N-terminal domain (NTD) that adopts a partially folded and dynamic conformation. Target specificity is achieved by simultaneous interactions of multiple NTDs with the aggregate surface. ClpL shows remarkable structural plasticity by forming diverse higher assembly states through interacting ClpL rings. NTDs become largely sequestered upon ClpL ring interactions. Stabilizing ring assemblies by engineered disulfide bonds strongly reduces disaggregation activity, suggesting that they represent storage states.

Mining Heat-Resistant Key Genes of Peony Based on Weighted Gene Co-Expression Network Analysis.

The RNA-Seq and gene expression data of mature leaves under high temperature stress of Paeonia suffruticosa 'Hu Hong' were used to explore the key genes of heat tolerance of peony. The weighted gene co-expression network analysis (WGCNA) method was used to construct the network, and the main modules and core genes of co-expression were screened according to the results of gene expression and module function enrichment analysis. According to the correlation of gene expression, the network was divided into 19 modules. By analyzing the expression patterns of each module gene, Blue, Salmon and Yellow were identified as the key modules of peony heat response related functions. GO and KEGG functional enrichment analysis was performed on the genes in the three modules and a network diagram was constructed. Based on this, two key genes PsWRKY53 (TRINITY_DN60998_c1_g2, TRINITY_DN71537_c0_g1) and PsHsfB2b (TRINITY_DN56794_c0_g1) were excavated, which may play a key role in the heat shock response of peony. The three co-expression modules and two key genes were helpful to further elucidate the heat resistance mechanism of P. suffruticosa 'Hu Hong'.

Enhanced Heat Resistance in Morchella eximia by Atmospheric and Room Temperature Plasma.

This study focuses on optimizing the mutagenesis process for Morchella eximia (Mel-7) mycelia through atmospheric and room temperature plasma (ARTP) mutation and explores the resultant thermal adaptability and physiological responses of mutant strains. This research demonstrated a clear relationship between ARTP mutagenesis exposure duration and lethality rate, indicating that an exposure time of 40 s resulted in the optimal balance of inducing mutations without causing excessive mortality. Additionally, this study established 43 °C as the ideal screening temperature for identifying mutant strains with enhanced heat resistance, as this temperature significantly challenges the mycelia while allowing thermotolerant strains to be distinguishable. Among the screened mutants, strains L21, L23, L44, and L47 exhibited superior growth and high-temperature tolerance, with notable resilience at 30 °C, highlighting their enhanced adaptability to above-optimal temperatures. Furthermore, this research delved into biochemical responses, including lipid peroxidation and non-enzymatic antioxidant content, highlighting the diverse mechanisms, such as enhanced lipid peroxidation resistance and increased antioxidant content, employed by mutant strains to adapt to temperature fluctuations. The activities of antioxidant enzymes, including peroxidase (POD) and superoxide dismutase (SOD), were shown to be significantly influenced by temperature elevations, illustrating their critical roles in the thermal adaptation of mutant strains. These findings shed light on the importance of considering mutation duration and temperature screening in the development of thermotolerant fungal strains with potential applications in various industries. This study's breakthrough lies in its comprehensive understanding of the thermal adaptability of Mel-7 mycelia and the identification of promising mutant strains, offering valuable insights for both academic and industrial purposes.

Scalable manufacturing of an amide-based nucleating agent for transparency and high heat resistance of polylactic acid.

The prevalent use of disposable plastic tableware presents notable environmental and health risks. An alternative, polylactic acid (PLA), often does not meet usage requirements due to its low crystallization rate. This research introduces an amide-based nucleating agent, BRE-T-100, developed through a straightforward method to enhance the heat resistance and crystallization rate of PLA. This study systematically investigates the impact of BRE-T-100 and other nucleating agents on the properties of PLA composites. The incorporation of 0.8 % BRE-T-100 increases the crystallization temperature of PLA from 109.6 °C to 131.9 °C. Further, the total crystallization time of PLA composites at 120 °C is reduced to <60 s, while maintaining good transparency. BRE-T-100 exhibits superior comprehensive properties compared to talcum, TMC-200, and TMC-300 and is nearly on par with LAK-301. Its application as a nucleating agent in PLA-based disposable tableware shows promise.

Bio-based poly(lactic acid) foams with enhanced mechanical and heat-resistant properties obtained by facilitating stereocomplex crystallization with addition of D-sorbitol.

The preparation of bio-based poly(lactic acid) (PLA) foams with high mechanical properties and heat resistance is of great significance for environmental protection and green sustainable development. In this paper, D-sorbitol (DS) containing six hydroxyl groups was introduced into poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blends for first time to promote the formation of stereocomplex (SC) crystals, which could improve the foaming behavior and enhance mechanical properties and heat resistance of PLA foams. The results showed that DS could improve the formation efficiency and crystallinity of SC crystals by enhancing the hydrogen bonding between the enantiomeric molecular chains. Furthermore, the compression modulus and interactions Vicat softening temperature of the PLLA/PDLA/DS blend foam increased about 854% and 16% compared to the pure PLLA foam, respectively. Besides, when the annealing process was introduced, the compression and heat resistance of the PLA foams increased further. This study provided a feasible strategy for the preparation of bio-based and biodegradable PLA foams with outstanding compressive and heat resistance properties.

Silicon Hybridization for the Preparation of Room-Temperature Curing and High-Temperature-Resistant Epoxy Resin.

Specialized epoxy resin, capable of achieving room-temperature profound curing and sustaining prolonged exposure to high-temperature environments, stands as a pivotal material in modern high-end manufacturing sectors including aerospace, marine equipment fabrication, machinery production, and the electronics industry. Herein, a silicon-hybridized epoxy resin, amenable to room-temperature curing and designed for high-temperature applications, was synthesized using a sol-gel methodology with silicate esters and silane coupling agents serving as silicon sources. Resin characterization indicates a uniform distribution of silicon elements in the obtained silicon hybrid epoxy resin. In comparison to the non-hybridized epoxy resin, notable improvements are observed in room-temperature curing performance, heat resistance, and mechanical strength.

Poly(ester imide)s with Low Linear Coefficients of Thermal Expansion and Low Water Uptake (VII): A Strategy to Achieve Ultra-Low Dissipation Factors at 10 GHz.

In this study, a series of ester-linked tetracarboxylic dianhydrides (TCDAs) with 2,6-naphthalene-containing longitudinally extended structures consisting of different numbers of aromatic rings (NAr = 6-8) was synthesized to obtain novel modified polyimides, poly(ester imide)s (PEsIs). These TCDAs were fully compatible with the conventional manufacturing processes of conventional polyimide (PI) systems. As an example, the PEsI film obtained from the ester-linked TCDA (NAr = 8) and an ester-linked diamine achieved unprecedented outstanding dielectric properties without the support of fluorinated monomers, specifically an ultra-low dissipation factor (tan δ) of 0.00128 at a frequency of 10 GHz (50% RH and 23 °C), in addition to an extremely high glass transition temperature (Tg) of 365 °C, extremely low linear coefficient of thermal expansion (CTE) of 6.8 ppm K-1, suppressed water uptake (0.24%), requisite film ductility, and a low haze. Consequently, certain PEsI films developed in this study are promising candidates for heat-resistant dielectric substrates for use in 5G-compatible high-speed flexible printed circuit boards (FPCs). The chemical and physical factors denominating tan δ are also discussed.