Poly(ester amide)s (PEAs) attract much attention as a new kind of biodegradable polymers. However, the synthesis of PEAs with sequence-regulated chain structures is still complicated due to the multistep polymerization, high monomer purity, as well as the usage of organic solvents, which greatly inhibits its development and applications. Herein, a one-pot strategy without solvent was developed to synthesize the alternating PEA from α,ω-amino alcohol and dicarboxylic acid by sequential polycondensation, where water was used as the controlling agent for amidation and esterification. Specifically, the amidation and esterification were controlled to proceed in turn by adding or removing water, realizing the one-pot preparation of alternating PEAs. The resultant PEA is characterized by ¹H- and ¹³C-NMR, and its chain structure is confirmed to be highly quasi-alternating similar to alternating PEAs prepared by classical methods The evaluations from DSC and DMA demonstrate that the properties of quasi-alternating PEA (T_m=102 °C, ΔH_m=30 J·g⁻¹) are far superior to those of random PEA (T_m=72 °C, ΔH_m<1 J·g⁻¹).

Lithium-ion batteries (LIBs) benefit from an effective electrolyte system design in both terms of their safety and energy storage capability. Herein, a series of precursor membranes with high porosity were produced using electrospinning technology by mixing PVDF and triblock copolymer (PS-PEO-PS), resulting in a porous structure with good interconnections, which facilitates the absorbency of a large amount of electrolyte and further increases the ionic conductivity of gel polymer electrolytes (GPEs). It has been demonstrated that post-cross-linking of the precursor membranes increases the rigidity of the nanofibers, which allows the polymer film to be dimensionally stable up to 260 °C while maintaining superior electrochemical properties. The obtained cross-linked GPEs (CGPEs) showed high ionic conductivity up to 4.53×10⁻³ S·cm⁻¹. With the CGPE-25, the assembled Li/LiFePO₄ half cells exhibited good rate capability and maintained a capacity of 99.4% and a coulombic efficiency of 99.3% at 0.1 C. These results suggest that the combination of electrospinning technique and post-cross-linking is an effective method to construct polymer electrolytes with high thermal stability and steadily decent electrochemical performance, particularly useful for Lithium-ion battery applications that require high-temperature usage.

Conjugated homopolymers based on six-member rings, e.g., polyfluorene, always exhibit blue emission and conjugated homopolymers based on five-member rings, e.g., polythiophene, can give red emission with low efficiency. In this work, we report a series of new conjugated homopolymers based on six-member rings with high-efficiency deep-red emission. The repeating units of the red light emitting homopolymers are double B←N bridged bipyridine (BNBP) with the boron atoms functionalized with diphenyl, borafluorene, and 2,7-di-tert-butyl-borafluorene groups, respectively. The relationship between the chemical structures and the opto-electronic properties of the monomers and the homopolymers has been systematically studied. The three polymers emit pure red light (λ_max=656 nm) or deep red light (λ_max=693 nm) with fluorescence quantum efficiency in solution higher than 60%. The polymers can be used as the emitters in solution-processed organic light-emitting diodes with red emission and decent device performance. This work indicates a new strategy to design highly efficient light emitting conjugated polymers.

The burgeoning growth of the new energy vehicles and aviation industry has escalated the need for energy storage capacitors capable of stable operation in harsh environments. The advent of metal-polyimide complexes has illuminated a novel approach for preparing temperature-resistant capacitors. However, the general application of these metal-polyimide complexes is impeded by the high dielectric loss and low breakdown strength, consequences of main-chain coordination and excessive metal ions content. Herein, our study proposes a novel polyimide-Cu complex material (POP-Cu) predicated on side-chain-type pyridine-Cu coordination, utilizing the structural backbone PMDA-ODA of mature commercial PI (Kapton) with reliable performance. Owing to the high degree of freedom afforded by the side chain with suppressed relaxation activation energy and the long-range electron delocalization formed by d-π coordination, the dielectric constant of this material containing merely 2.7 mol% Cu increases from 3.25 (POPI) to 5.58, while maintaining a remarkably low dielectric loss of 0.0066. Meanwhile, this material exhibits a substantial DC breakdown strength of 436.2 MV·m⁻¹ and a high energy density of 5.42 J·cm⁻³, coupled with superior mechanical and thermal properties. Even at 150 °C, it retains over 90% of its room-temperature energy density, demonstrating notable dielectric stability under high temperatures. These attributes underscore its promising application for capacitors operating in harsh environments.

The aim of this study was to develop self-healable and robust electroconductive film based on polyaniline copolymer for application as electrode in flexible supercapacitor. For this purpose, the electroconductive polymer brushes (EPB) was elaborated. The synthesis of EPB is based on graft polymerizations of acrylamide (AAm) on poly(vinyl alcohol) (PVA) with formation of PVA-PAAm polymer brush and subsequent graft copolymerization of aniline and p-phenylenediamine on PVA-PAAm resulting in formation of EPB with electroconducting copoly(aniline-co-p-phenylenediamine) (PAPhDA). It was found that the ratio between PVA and PAAm at the first stage greatly influence the electrochemical performance of the EPBs. Electroconducting films were prepared by casting of EPB solution with subsequent drying. Investigation of electrical current distribution through the film with AFM reveal more uniform distribution of PAPhDA in EPB in comparison with reference PVA-PAPhDA and PAAm-PAPhDA samples. It was demonstrated that mechanical characteristics and electrical conductivity values of films restore at large extent after curring and self-healing under optimal relative humidity level (58%). The flexile supercapacitor cell with EPB film electrodes demonstrate specific capacitance 602 mF·cm^–2 at the current density of 1 mA·cm^–2 and retention 94% of initial capacitance after 5000 charge/discharge cycles.

In prevailing p-i-n perovskite solar cells (PSCs), solution-processible fullerene molecules are widely used as electron-transporting layers (ETLs) but they typically suffer from poor uniformity and undesirable stability issues. Additionally, a separate bathocuproine (BCP) layer is needed to block hole transfer, increasing fabrication complexity and cost. Here, we address these limitations by developing a novel polymeric ETL (named PFBCP) synthesized by polymerizing C₆₀ with BCP. This innovative material achieves both efficient electron transport and hole blocking, while its excellent uniformity minimizes interface recombination and enhances stability. Consequently, our blade-coated PSCs utilizing PFBCP achieve a high power conversion efficiency exceeding 22% and retain 91% of initial efficiency after 1200 h of light exposure. This development not only paves the way for commercially viable PSCs but also opens avenues for future ETL design to realize even more efficient and stable PSCs.

Glucose-sensitive membrane has potential application in self-regulating insulin release. Phenylboronic acid (PBA) is a well-known glucose reporter. Unfortunately, most PBA-based glucose-sensitive materials are expansion-type, which are not suitable as chemical valves in membrane pores for self-regulating insulin release. According to a new glucose-sensitive mechanism, we synthesized PBA-based contraction-type glucose-sensitive liner polymer and microgels. Herein, a glucose-sensitive membrane was prepared by grafting PBA-based contraction-type glucose-sensitive linear polymer on the membrane surface. Through adjusting the chain length and chain density, the glucose-sensitivity of the membrane was optimized. The membrane can reversibly regulate insulin release at physiologically relevant glucose concentrations in simulates body fluids and fetal bovine serum. The membrane also has good stability, anti-fouling and biocompatibility. It has potential application in self-regulating insulin release.

Owing to its high production volume and wide range of applications, polyethylene has gained a great deal of attention, but its low surface energy and non-polar nature have limited its application in some important fields. In this study, ethylene/11-iodo-1-undecene copolymers were prepared and used as the intermediates to afford a series of imidazolium-based ionomers bearing methanesulfonate (CH₃SO₃⁻), trifluoromethanesulfonate (CF₃SO₃⁻), or bis(trifluoromethane)sulfonimide (Tf₂N⁻) counteranions. The tensile test results showed that the stress-at-break (7.8−25.6 MPa) and the elongation-at-break (445%−847%) of the ionomers could be adjusted by changing the counterion species and the ionic group contents. Most importantly, the ionomers exhibited marvelous antibacterial activities against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The ionomers bearing Tf₂N⁻ exhibited antibacterial activities >99% against both S. aureus and E. coli when ionic content reached 9.1%. The imidazolium-based ionomers prepared in this work demonstrated excellent comprehensive properties, especially high-efficient and broad-spectrum antibacterial ability, exhibiting the potential for the application as the antibacterial materials in packaging, medical, and other fields.

Olefin polymerization is one of the most important chemical reactions in industry. This work presents a strategy that emphasizes the synergistic meta/para-steric hindrance of N-aryl groups and electronic effects in newly synthesized neutral salicylaldiminato nickel catalysts. These nickel(II) catalysts exhibit exceptional thermostability, ranging from 30 °C to 130 °C, demonstrating enhanced catalytic activities and broadly regulated polyethylene molecular weights (3−341 kg·mol⁻¹) and controlled polymer branch density (2−102 brs/1000C). The preferred catalyst Ni3 with concerted steric and electronic effects enables the production of solid-state semi-crystalline polyethylene materials at temperatures below 90 °C. Notably, Ni3 exhibits an impressive tolerance of 110 °C and can withstand even the challenging polymerization temperature of 130 °C, leading to the production of polyethylene wax and oil. Also, functionalized polyethylene is produced.

Toughening the petroleum-based epoxy resin blends with bio-based modifiers without compromising their modulus, mechanical strength, and other properties is still a big challenge in view of the sustainability. In this study, a bio-based liquid crystal epoxy resin (THMT-EP) with an s-triazine ring structure was utilized to modify a petroleum-based bisphenol A epoxy resin (E51) with 4,4'-diaminodiphenylsulfone (DDS) as a curing agent, and the blended systems were evaluated for their thermal stability, mechanical properties, and flame retardancy. The results showed that the impact strength of the blended system initially increased and then decreased with the increase in THMT-EP content, and it reached the a maximum value of 26.5 kJ/m² when the THMT-EP content was 5%, which was 31.2% higher than that of E51/DDS. Notably, the flexural strength, modulus, and glass transition temperature of the blended system were all simultaneously improved with the addition of THMT-EP. At the same time, the addition of THMT-EP enhanced the flame retardancy of the system by increasing the char yield at 700 °C and decreasing the peak heat release rate and total heat release rate. This work paves the way for a more sustainable improvement in the comprehensive performance of epoxy resin.

Due to their excellent biocompatibility and biodegradability, aliphatic polyesters are widely used in the biomedical, packaging and agricultural fields, which are usually accessed by the ring-opening polymerization (ROP) of lactones and the catalysts particularly play an important role. Herein a series of quinolinyl-urea catalysts have been synthesized via the reaction between isocyanate and aminoquinoline with an amino group at different substitution positions and characterized. In combination with 7-methyl-1, 5, 7-triazabicyclo[4,4,0]dec-5-ene (MTBD) as a cocatalyst and benzyl alcohol (BnOH) as an initiator, 1-(3,5-bis(trifluoromethyl)phenyl)-3-(quinolin-3-yl)urea (3-QU) was observed to be most active for the ROP of δ-valerolactone (δ-VL). The polymerization conditions were optimized by varying the type of organic base, catalyst concentration and reaction temperature. By changing the ratio of [M]₀/[I], linear polyvalerolactones (PVLs) with different molecular weights and narrow molecular weight distribution were prepared. The kinetic and chain extension experiments were carried out to prove the “living”/controllable feature. And the NMR experiments were used to support the proposal of possible mechanism.

The thermochromic mechanism and the structure-property regulation principle of reversible thermochromic polydiacetylene (PDA) materials have always been a challenging issue. In this work, a series of diacetylene monomers (m-PCDA) containing phenyl and amide or carboxyl groups were synthesized from 10,12-pentacosadiynoic acid (PCDA) through the esterification or amidation reactions. The effects of the number and the distribution of the functional groups in m-PCDA molecules on their solid-state polymerization capability, and the thermochromic mechanism of their corresponding polymers (m-PDA) were investigated and discussed in detail. The results show that the m-PCDA monomers containing both benzene ring and groups that can form hydrogen bonding interactions have strong intermolecular interaction, and are easy to carry out the solid phase polymerization under 254-nm UV irradiation to obtain the corresponding new thermochromic m-PDA materials. The thermochromic behavior of m-PDA depends on its melting process. The initial color-change temperature (blue to red) is determined by the onset melting temperature, and the temperature range in which reversible color recovery can be achieved by repeat heating-cooling treatment is determined by its melting range. According to the proposed thermochromic mechanism of PDA, various new PDA materials with precise thermochromic temperatures and reversible thermochromic temperature ranges can be designed and synthesized through the appropriate introduction of benzene ring and groups that can form hydrogen bonding interactions into the molecular structure of linear diacetylene monomer. This work provides a perspective to the precise molecular structure design and the property regulation of the reversible thermochromic PDA materials.

The evolution of high-frequency communication has accentuated the significance of controlling dielectric properties in polymer media. Traditionally, it has been theorized that rigid molecular chains lead to lower dielectric loss. However, the validity of this proposition at high frequencies remains uncertain. To scrutinize the correlation between chain flexibility and dielectric properties, we synthesized six poly(ester imide)s (PEIs) with systematically varied molecular chain flexibilities by modifying the ester's substitution on the aromatic ring. The introduction of ester bonds bestowed all PEI films with a low dielectric dissipation factor (D_f), ranging from 0.0021 to 0.0038 at 10 GHz in dry conditions. The dry D_f displayed a pattern consistent with volume polarizability (P/V). Unexpectedly, PI-mmm-T, featuring the most flexible molecular chain, exhibited the lowest dielectric loss under both dry (0.0021 @ 10 GHz) and hygroscopic (0.0029 @ 10 GHz) conditions. Furthermore, the observed increase in D_f after humidity absorption suggests that the high dielectric loss of PEI in applications may be attributed to its hygroscopic nature. Molecular simulations and characterization of the aggregation structure revealed that the smaller cavities within flexible molecular chains, after close stacking, impede the entry of water molecules. Despite sacrificing high-temperature resistance, the precursor exhibited enhanced solubility properties and could be processed into high-quality films. Our research unveils new insights into the relationship between flexibility and high-frequency dielectric loss, offering innovative perspectives on synthesizing aromatic polymers with exceptional dielectric properties.

The traditional high-temperature preparation process of polyimide can cause many problems and limits the wider application in extreme conditions. An important challenge to be solved urgently is the reduction of imidization temperature. In this work, twelve kinds of polyimide films with different chain rigidity were prepared at low temperature of 200 °C, in the absence or presence of imidazole used as the catalyst. The molecular rigidity and free volume were theoretically calculated, and relationship between structure and properties were systematically studied. The results show that imidization reaction under low temperatures is significantly affected by the rigidity of molecular chains. The rigid structure of polyimide is not conducive to the low-temperature imidization, but this adverse effect can be eliminated by adding catalyst, resulting the notably increased imidization degree. The optical and thermal properties can be improved to a certain extent for the chemically catalyzed system, resulting in relatively higher heat resistance and thermal stability. While the mechanical performance could be determined by complicating factors, greatly different from polyimide films prepared by high temperature method. To investigate aggregation structures of films, the effect of chain rigidity and catalyst on the stacking or orientation of molecular chains was further elaborated. This work can contribute to the understanding of chemically catalyzed imidization that is rarely reported in the existing research, and will provide guidance for the low-temperature preparation of high-performance polyimides.

Shear-thinning hydrogels have emerged for endoscopic submucosal dissection, while wound intervention after surgery has rarely been mentioned. Herein, a catechol-modified chitosan hydrogel with shear-thinning property was developed for simultaneously facilitating endoscopic submucosal dissection and postoperative wound healing. Benefiting from the shear-thinning and self-healing characteristics, the as-prepared hydrogel showed easily endoscopic injectability. It also performed very well as submucosal cushion, which could remain above 70% after injection for 120 min in ex vivo porcine large intestine model. In fact, the cushion height of normal saline dramatically decreased to 46% of the initial height at 30 min. Ag nanoparticles encapsulated into the network endowed the hydrogel with almost reached 100% antibacterial effect against E. coli and S. aureus. The hemolysis ratio of the hydrogel was calculated to be as low as 0.8%. Combined with good hemocompatibility and cytocompatibility, the as-prepared hydrogel displayed much higher in vivo wound closure and healing efficacy than normal saline. These results demonstrated the superiority of the shear-thinning chitosan hydrogel in facilitating clinical endoscopic submucosal dissection surgery.

Plasma treatment is necessary to optimize the performance of biomaterial surfaces. It enhances and regulates the performance of biomaterial surfaces, creating an effective interface with the human body. Plasma treatments have the ability to modify the chemical composition and physical structure of a surface while leaving its properties unaffected. They possess the ability to modify material surfaces, eliminate contaminants, conduct investigations on cancer therapy, and facilitate wound healing. The subject of study in question involves the integration of plasma science and technology with biology and medicine. Using a helium plasma jet source, applying up to 18 kV, with an average power of 10 W, polymer foils were treated for 60 s. Plasma treatment has the ability to alter the chemical composition and physical structure of a surface while maintaining its quality. This investigation involved the application of helium plasma at atmospheric pressure to polyamide 6 and polyethylene terephthalate sheets. The inquiry involves monitoring and assessing the plasma source and polymer materials, as well as analyzing the impacts of plasma therapy. Calculating the mean power of the discharge aids in assessing the economic efficacy of the plasma source. Electric discharge in helium at atmospheric pressure has beneficial effects in technology, where it increases the surface free energy of polymer materials. In biomedicine, it is used to investigate cytotoxicity and cell survival, particularly in direct blood exposure situations that can expedite coagulation. Comprehending the specific parameters that influence the plasma source in the desired manner for the intended application is of utmost importance.

In this work, aramid nanoparticles (ANPs) were prepared in dimethyl formamide (DMF) solution containing high impact polystyrene (HIPS) via a bottom-up approach. Transmission electron microscopy (TEM) images showed that the obtained ANPs were evenly distributed in the HIPS matrix without any agglomeration. Chemical composition of the ANPs, i.e., poly(p-phenyl-p-phenylenediamine) (PPTA), was confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD). The ANP/HIPS composites, obtained after ethanol precipitation, were added to neat HIPS as fillers to fabricate ANP/HIPS composite sheets. The surface roughness and the glass transition temperature (T_g) of the sheets were characterized by atomic force microscope (AFM) and differential scanning calorimetry (DSC), respectively. Compared with neat HIPS, the mechanical properties of the composite sheet were significantly improved, and the Young's modulus increased from 246.55 MPa to 2025.12 MPa, the tensile strength increased from 3.07 MPa to 29.76 MPa, and the toughness increased from 0.32 N/mm² to 3.92 N/mm², with an increase rate of 721%, 869% and 1125%, respectively. Moreover, the thermal stability of the composites improved with the increase in ANP content.

The long chain branching (LCB) polyglycolide (PGA) was successfully prepared by the successive reactions of the terminal hydroxyl groups of PGA with triglycidyl isocyanurate (TGIC) and pyromellitic dianhydride (PMDA). The influence of LCB produced by functional group reaction on rheological and crystallization behavior was studied and discussed through linear rheology, uniaxial elongation and DSC (differential scanning calorimetry). The much higher viscosity and the more notable strain hardening behavior of modified PGA indicates the LCB with high degree of entanglements are created. The melt strength of PGA is finally improved greatly and can make sure that the supercritical CO₂ foaming can be carried out successfully.

The packaging materials with cushioning performance are used to prevent the internal contents from being damaged by the impact and vibration of external forces. The polyurethane microcellular elastomers (PUMEs) can absorb energy through cell collapse and molecular chain creep. In this study, PUMEs with different densities were investigated by scanning electron microscopy, dynamic mechanical analysis and dynamic compression tests. PUMEs exhibited significant impact resistance and the maximum peak stress attenuation ratio reached 73.33%. The protective equipment was made by PUME with the optimal density of 600 kg/m³, and then the acceleration sensing device installed with the same protective equipment fell from a height of 3, 5 and 10 m to evaluate the energy-absorbing property and reusability of PUMEs. The results showed that PUMEs equipment reduced the peak acceleration of the device by 93.84%, with a maximum deviation of 9% between actual test and simulation, and shortened the impact time of first landing by 57.39%. In addition, the equipment PUMEs equipment could effectively reduce the stress on the protected items.

The antioxidant N-isopropyl-N'-phenyl-p-phenylenediamine (4010NA) was dissolved in ethanol and impregnated into silica aerogel (SAG) via vacuum-pressure cycles, yielding composite particles (A-N) with enhanced sustained-release and reinforcing capabilities. The effect of A-N on the mechanical properties and thermal-oxidative aging resistance of styrene-butadiene rubber (SBR) vulcanizates was investigated. TGA and BET assessments indicated that the loading efficiency of 4010NA in SAG reached 14.26% within ethanol's solubility limit. Incorporating A-N into SBR vulcanizates significantly elevated tensile strength by 17.5% and elongation at break by 41.9% over those with fumed silica and free 4010NA. Furthermore, A-N notably enhanced the thermal-oxidative aging resistance of SBR. After aging for 96 h at 100 °C, the tensile strength and elongation at break of SBR with A-N sustained 70.09% and 58.61% of their initial values, respectively, with the retention rate of elongation at break being 62.8% higher than that of SBR with fumed silica and free antioxidant. The study revealed that A-N composite particles significantly inhibited the crosslinking in SBR's molecular chains, reducing hardening and embrittlement during later thermal-oxidative aging stages.

Constructing three dimensional (3D) covalent organic frameworks (COFs) through the entanglement of two dimensional (2D) nets is a promising but underdeveloped strategy. Herein, we report the design and synthesis of a fluorine functionalized 3D COF (3D-An-COF-F) formed by entangled 2D sql nets. The structure of 3D-An-COF-F was determined by the combination of continuous rotation electron diffraction technique and modelling based on the chemical information from real space. Interestingly, compared to the isostructural 3D-An-COF without F atoms, 3D-An-COF-F showed an improved CO₂ sorption ability and higher CO₂/N₂ selectivity. Our study not only demonstrated the generality of constructing 3D COFs with entangled 2D nets by introducing bulky groups vertically in planar building blocks, but also will expand the diversity of 3D COFs for various applications.

Janus films with asymmetric physical/chemical properties have attracted considerable attention due to their promising applications in personal thermal management, electronic skins, sensors, actuators, etc. However, traditional methods for fabricating Janus films conventionally need the assistance of an interface or auxiliary equipment, which are usually complex and time-consuming. Herein, flexible poly(vinyl alcohol) (PVA)/graphene oxide (GO)/h-BN (recorded as PVA/GO/h-BN) Janus films with thermally, optically, and electrically anisotropic properties are fabricated by a simple density deposition self-assembly method, which just utilizes the density difference between GO and h-BN during water evaporation. Experimental results show that the two sides of the acquired Janus films have obvious asymmetric characteristics. In the original state of the PVA/GO/h-BN Janus films, the thermal conductivity of the GO side (10.06 W·m^–1·K^–1) is generally lower than that of the h-BN side (10.48 W·m^–1·K^–1). But after GO is reduced, the thermal conductivity of the rGO side reaches 12.17 W·m^–1·K^–1, surpassing that of the h-BN side. In addition, the relative reflectance of the h-BN side of Janus film is also significantly higher than that of the rGO side, and the surface resistance difference between the two sides is about 4 orders of magnitude. The prepared PVA/GO/h-BN Janus films show great application potential in human thermal management, light conversion switches, and electronic skins. This study provides a simple and versatile strategy for fabricating Janus films with multifunctional (such as thermal, optical, and electrical) anisotropies.

Shish crystals are crucial to achieving high performance low-dimensional ultra-high molecular weight polyethylene (UHMWPE) products. Typically, high stretch and shear flow fields are necessary for the formation of shish crystals. In this study, UHMWPE gel films with reserved shish crystals were prepared by gel molding, the structural evolution and properties of UHMWPE films stretched at temperatures of 100, 110, 120 and 130 °C were investigated by in situ small-angle X-ray scattering (SAXS)/ultra-small-angle X-ray scattering (USAXS)/wide-angle X-ray diffraction (WAXD) measurements as well as scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) measurements. Our findings showed that the reserved shish crystals can facilitate the formation and structural evolution of shish-kebab crystals during the hot stretching. Additionally, the reserved shish crystals promote the structural evolution of UHMWPE films to a greater extent when stretched at 120 and 130 °C, compared to 100 and 110 °C, resulting in higher crystallinity, orientation, thermal properties, breaking strength and Young's modulus. Compared to UHMWPE high-entangled films with reserved shish crystals prepared by compression molding, UHMWPE low-entangled films with reserved shish crystals prepared by gel molding are more effective in inducing the formation and evolution of shish-kebab crystals during the hot stretching, resulting in increased breaking strength and Young's modulus.

Due to the mechanical stability of PP layer, the PP/HDPE double-layer microporous membrane could be prepared at a higher heat-setting temperature than that of PE monolayer membrane. In this work, the effects of heat-setting temperature on the pore structure and properties of PP/HDPE double-layer membrane were studied. With the increase of heat-setting temperature from 120 °C to 130 °C, the length of connecting bridge crystal and crystallinity in the PE layer increase due to the melting of thin lamellae and the stability of connecting bridge structure during heat-setting. The corresponding air permeability, porosity, wettability of liquid electrolyte and mechanical property of the heat-set microporous membrane increase, exhibiting better electrochemical performance. However, when the heat-setting temperature is further increased to 140 °C, higher than the melting point of PE resin, some pores are closed since the lamellae and connecting bridges melt and shrink during heat-setting, resulting in a decrease of air permeability and porosity. In contrast, there is negligible change in the PP layer within the above heat-setting temperature region. This study successfully builds the relationship between the stable pore structure and property of microporous membrane during heat-setting, which is helpful to guide the production of high-performance PP/PE/PP lithium batteries separator.