High Performance Polymers

The rapid advancement of aerospace and wind power industries necessitates epoxy resin matrices with simultaneous high strength and high toughness. However, conventional modification methods struggle to mitigate the trade-off between strength and toughness in epoxy resins, rendering the development of epoxy resins with both high strength and high toughness a persistent challenge. In this study, two Xylok epoxy resins (X-PPEP and X-BPEP) were synthesized utilizing para-xylene dimethyl ester (PXDM) and 4,4′-bis(methoxymethyl)biphenyl (BMMB) as raw materials, respectively. Subsequently, with 4,4′-diaminodiphenylmethane (DDM) serving as the curing agent, the properties of the corresponding castings and composites were investigated. The results reveal that the crosslinked networks of X-PPEP/DDM and X-BPEP/DDM exhibit highly rigid backbones and substantial free volume fraction, thereby endowing them with exceptional mechanical properties. Specifically, the tensile strength and elongation at break of both systems exceeded 90 MPa and 7%. The impact strength of X-BPEP/DDM reached 49.72 kJ/m². Furthermore, the glass fiber-reinforced composites based on these resins also exhibited excellent mechanical properties. These findings provide a viable strategy for fabricating epoxy resins with balanced strength and toughness, highlighting the significant application potential of X-PPEP and X-BPEP in high-performance sectors such as aerospace and wind power generation.

A novel fluorinated phthalonitrile monomer is synthesized via nucleophilic substitution reactions using 4,4′-difluorobenzophenone, bisphenol AF, and 4-nitrophthalimide. Two resins with distinct curing temperatures are obtained using 4-(aminophenoxy) benzonitrile (APPH) as the curing agent. The successful synthesis of the monomer is confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) is employed to determine the melting point and curing behavior of the monomer, revealing a melting point of 102°C and a calculated processing window of 148°C. Furthermore, a relatively low average apparent activation energy was calculated. The morphology of the polymer cross-section was characterized using scanning electron microscopy (SEM), and the resin cross-section exhibited characteristics consistent with brittle fracture. Thermodynamic properties of the polymers are investigated via dynamic mechanical analysis (DMA), revealing storage modulus of 2313 MPa and 2433 MPa for the two resins at room temperature. Thermal stability is evaluated by thermogravimetric analysis (TGA), revealing that both resins exhibited temperatures for 5% weight loss above 500°C under both nitrogen and air atmospheres.

In this study, a novel flame retardant designated as SFD, which contains phosphorus (P), nitrogen (N), and sulfur (S), was successfully synthesized via a one-pot method utilizing 2-aminobenzothiazole, furfural, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials. This flame retardant was subsequently incorporated as an additive into epoxy resin (EP), with various formulations prepared using dicyandiamide (DDM) as the curing agent. The epoxy formulations containing only 3 wt% of SFD exhibited an improved Limiting Oxygen Index (LOI) of 34% and achieved UL-94 V-0 ratings. The Peak Heat Release Rate (PHRR), Total Heat Release (THR), and Total Smoke Production (TSP) for the EP/SFD composites were reduced by 28.0%, 30.1%, and 30.0%, respectively, in comparison to pure EP. Mechanical property assessments of the SFD/EP composites indicated that the incorporation of SFD had minimal impact on the mechanical properties of EP; thus, SFD can enhance the flame retardancy of EP without compromising its mechanical integrity. Analysis of the flame retardant mechanism revealed a significant P-N synergistic effect between the benzothiazole moiety and the phosphorus heterophenanthrene moiety present in SFD. The addition of SFD effectively mitigates heat release and smoke production during combustion processes involving EP while demonstrating excellent flame-retardant characteristics along with smoke suppression capabilities; furthermore, it promotes carbon layer formation. This research presents a straightforward strategy for synthesizing a multi-element synergistic flame retardant system that holds promise for application across a broad spectrum of thermoset plastics.

A series of s-triazine-based homopolyesters was synthesized via polycondensation of a 4,6-bis-(N-(4-(benzoylchloride)amino))-2-(N-benzyl-piperazin-1-yl)-1,3,5-triazine (monomer) with various aliphatic and aromatic diols. The structures were confirmed using FT-IR and ¹H NMR spectroscopy. Physicochemical characterization revealed that polyesters containing aromatic moieties exhibited higher density, intrinsic viscosity, and improved thermal stability compared to those derived from aliphatic diols. Solubility studies indicated enhanced dissolution behaviour in polar aprotic solvents at elevated temperatures. Thermogravimetric analysis demonstrated significant thermal resistance, particularly for bisphenol-based systems. The thermal degradation kinetics were evaluated using Coats–Redfern, Horowitz–Metzger, Broido, and Chan methods, showing consistent trends with variations attributed to model assumptions. The overall degradation trends remained consistent. The combined physicochemical and thermal characteristics suggest that these s-triazine-based homopolyesters may be promising candidates for advanced materials requiring thermal resistance and structural stability.

Graphical Abstract

Phthalonitrile (PN) resins exhibit outstanding thermal and mechanical properties but suffer from intrinsically high melting temperatures and sluggish curing kinetics, which severely restrict their processability and manufacturability. In this work, a eutectic blending strategy based on ternary PN monomers was employed to markedly depress the melting temperature, enabling mild and controllable melt prepolymerization with a diamine curing agent. This approach produced a low-melting phthalonitrile prepolymer (MPPh) exhibiting a viscosity below 1 Pa·s at 88°C, providing a stable melt-processing window. DSC and FTIR analyses revealed that the prepolymerization predominantly proceeded through linear chain growth via amino-nitrile addition reactions. To address the inherently low curing reactivity of MPPh, 3-aminophenylacetylene (APA) was introduced as a reactive diluent to activate the curing process and further tailor the rheological behavior. The modified resin (MP-m) demonstrated significantly enhanced curing efficiency and a reduced viscosity below 1 Pa·s at 66°C, excellent isothermal stability, and pronounced shear-thinning behavior. The cured MP-m resin retained excellent thermal stability and mechanical performance. These findings provide a simple and solvent-free strategy for the preparation of low-melting-point phthalonitrile, broadening the practical application potential of PN resins in high-temperature composite manufacturing.

A new diether-diamine monomer, 1,1-bis [4-(4-aminophenoxy)-3-methylphenyl]cyclopentane (BAMPC), containing a cardo cyclopentane unit and a pendant methyl substituent, was synthesized through a multistep procedure. The structure of the methyl-substituted diether-diamine monomer was confirmed using FT-IR, ¹H NMR, ¹³C NMR, and mass spectrometry. Polycondensation of BAMPC with aromatic dialdehydes, including terephthalaldehyde and isophthalaldehyde, produced a series of co-poly (azomethine-ether)s incorporating cardo cyclopentane units in the polymer backbone. The influence of the cardo cyclopentane structure and pendant methyl group on the solubility and thermal stability of the resulting co-poly (azomethine-ether)s was examined. The polymers exhibited glass transition temperatures (Tg) in the range of 165-178°C and thermal degradation temperatures (T_d) between 456 and 486°C, indicating thermal stability. The polyazomethines were soluble in polar aprotic solvents such as DMF, NMP, DMAc, and DMSO at ambient temperature or upon heating. X-ray diffraction analysis indicated that SPAM-2, SPAM-3, SPAM-4, and SPAM-5 exhibited amorphous characteristics with a broad diffraction peak around 2θ ≈ 20°, whereas SPAM-1 showed semicrystalline behaviour. The inherent viscosities of the co-poly (azomethine-ether)s ranged from 0.20 to 0.39 dL g^-1.

Graphical Abstract

Epoxy resin (EP) is valued for its adhesion and chemical stability, yet its inherent brittleness and flammability limit advanced applications. To address this, a novel reactive ionic liquid flame retardant, [PMoam]Ps, was developed as a co-curing agent. It integrates into the EP network, significantly enhancing flame retardancy. The modified composite achieves a limiting oxygen index (LOI) of 29.3%, a UL-94 V-0 rating, and shows reductions in peak heat release rate (PHRR) and total heat release (THR) of 35.8% and 38.6%, respectively. Simultaneously, the ionic liquid acts as an internal plasticizer, markedly improving mechanical performance. Compared to neat EP, the composite exhibits increases of 46.1% in tensile strength, 57.4% in flexural modulus, and 87.7% in impact strength. This work provides a promising strategy for developing high-performance epoxy composites with balanced flame retardancy and mechanical properties.

This study establishes a systematic mechanistic framework for phthalonitrile resins containing polyimide skeletons (PIPN) to address their narrow processing window and unclear thermo-mechanical regulation. Six PIPN model compound with varied dianhydride structures PM (PMDA), BP(BPDA), F (6FDA), ABP(ABPDA), K(BTDA), E (BPADA) were designed and synthesized. Through integrated multiscale simulations and experimental characterization, a comprehensive “structure–weak interactions–packing order–molecular mobility–energetics–macroscopic properties” correlation model was constructed for the first time. Molecular backbone rigidity, symmetry and planarity govern the performance: fully rigid PM-PIPN exhibited strongest π-π stacking and electrostatic interactions, yielding the highest melting point (390°C) and superior predicted modulus. Conversely, flexible segments (E-PIPN) or sterically hindered groups (F-PIPN) systematically weakened intermolecular interactions, reducing both melting point and modulus while increasing Poisson’s ratio. Electrostatic potential analysis, weak interaction visualization (IRI), mean square displacement (MSD) and cohesive energy density calculations synergistically revealed the regulation mechanisms from electronic, spatial, dynamic and energetic perspectives. This mechanistic framework provides theoretical foundations for rational molecular design of high-performance PIPN resins.

The inherent brittleness of epoxy (EP) has long imposed limitations on its utilization within advanced field. This study synthesized a novel high-performance soluble polymer with a tetramethyl biphenyl structure (named tetramethyl biphenyl poly arylene ether ketone, S-TBPAEK) as a toughening agent for preparing EP composites. The aromatic structure in S-TBPAEK enhanced the heat resistance of composites, while its unique tetramethyl structure promoted excellent compatibility with EP. Additionally, it was observed that when S-TBPAEK content reached 12.5 phr, the impact strength of composite was significantly increased by 170 %. Additionally, the mechanical properties of the composite, such as flexural strength and tensile strength, have been enhanced by approximately 43.7 % and 55.8 % respectively. Finally, the fracture surfaces of the composites were analyzed using SEM to investigate the fracture mechanism. The results revealed that the fracture behavior of impact, flexural and tensile specimens transitioned from brittle to ductile fracture. The phenomenon suggested that the S-TBPAEK/EP composite absorbed more energy during fracturing process, thereby enhancing its toughness. In summary, S-TBPAEK shows great promise as a toughening agent for epoxy composites, offering new insights into the field of epoxy toughening.

Phthalonitrile (PN) resin has attracted significant attention due to its exceptional thermal stability and mechanical properties. However, the requirement for elevated curing temperatures remains a critical challenge for their widespread practical applications. In this study, phthalonitrile containing branched cyanine (BPN) was blended with silicon-containing arylacetylene (PSA) to investigate their synergistic curing effects. The 10 wt% PSA formulation offers an optimal trade-off, demonstrating that moderate PSA loading synergistically enhances both processability and thermal stability without compromising high-temperature mechanical robustness: a reduction of the initial curing temperature from 234.3°C to 198.7°C and a decrease in the melting point from 161.6°C to 147.4°C. Conversely, the processing window expanded from 41.3°C to 54.7°C. Furthermore, the system exhibited enhanced thermal stability, evidenced by an increase in the 5% weight loss temperature (T _d5 ) from 530.33°C to 552.38°C and a rise in the char yield from 75.73% to 80.13%. No distinct glass transition was detected below 400°C, indicating a substantial improvement in both the processability and thermal stability of the blend system. Although the incorporation of PSA resulted in a slight reduction in the mechanical properties of BPN, the blends retained excellent mechanical performance at elevated temperatures, surpassing the room-temperature properties of PSA. The findings significantly enhance the industrial viability of phthalonitrile-based materials, effectively paving the way for their large-scale deployment in high-performance sectors.

In this study, poly(furfuryl alcohol) (PFA) was chemically modified by Diels–Alder addition of maleic anhydride (MA; 1, 2, 3, 5, and 15 phr) to increase carbonyl functionality and enable ambient-temperature curing with an amine hardener. Modified PFA (mPFA) samples were cured with a polyamine (HY) and, because carbonyl content alone was insufficient to achieve satisfactory mechanical performance, blended with a commercial epoxy (Araldite LY 5052) at varying weight ratios (10–50 phr). The modification reaction and curing kinetics were followed by FTIR and chemorheology; chemical structure was confirmed by ¹H/¹³CNMR. Hardness, tensile (ASTM D638 type V), DMTA and TGA characterized the cured networks. FTIR and rheology showed that 1–3 phr MA produces effective modification and that 30 phr HY is sufficient for ambient curing. Incorporation of 50 phr epoxy substantially improved mechanical and thermal performance: PFA-50 exhibited hardness 253 ± 2 cycles, tensile strength 7.58 ± 0.38 MPa, Young’s modulus 71.01 ± 1.19 MPa and Tg 57.48°C, while the best-performing MA-modified formulation (PFA/2MA-50) reached hardness 309 ± 2 cycles, tensile strength 10.19 ± 0.54 MPa, Young’s modulus 126.9 ± 2.22 MPa and T_g 66.94°C. TGA showed increased char yield for PFA/2MA-50 (15.7 wt.% at 800°C) versus epoxy alone (9.7 wt.%). DFT calculations (B3LYP/6-31G (d,p), implicit DMF) support amide formation as a favorable curing pathway for MA-modified segments and are consistent with ATR-FTIR assignments. The combined MA modification and epoxy integration yields ambient-curing, mechanically robust PFA-based networks with improved thermal stability, making them promising binders for intumescent coatings.

Epoxy-based adhesives are one of the most important types of adhesives in the industrial field due to their excellent bond strength, low shrinkage, and favorable processability. However, epoxy-based adhesives tend to have disadvantages such as inadequate toughness and strength, which limits their use in structural bonding applications. In this paper, a novel silicone modified epoxy structural adhesive film was prepared through a condensation reaction between the terminal hydroxyl groups of polydimethylsiloxanes and the hydroxyl groups of epoxy resin. The silicone modified epoxy films have excellent lap shear and peel strength. Moreover, nanosilica was added to further improve the performance of adhesive films. The rheological, mechanical and thermal properties of the films were measured, FT-IR and SEM were used to further analyze the toughening mechanism. The results indicated that the low content of nanosilica can play an excellent modification effect on the adhesive films. The rigid-flexible integrated structure formed by nanosilica and silicone in the adhesive film system improves the mechanical properties, and reduced maximum thermal decomposition rate of the adhesive films.

High-performance co-polyimide (co-PI) fibers derived from 3,3`4,4`-biphenyldianhydride (BPDA), p-phenylenediamine (p-PDA) and 2-(4-aminophenyl)-5-amino-benzimidazole (BIA) were prepared via the wet spinning and dry-jet wet spinning method, respectively. The distinctions between wet spinning and dry-jet wet spinning processes on the structures and properties of co-PI fibers were systematically investigated. The co-PI fibers prepared by dry-jet wet spinning exhibited smoother surface morphology and higher mechanical properties than those of co-PI prepared by wet spinning. Wide-angle X-ray diffraction (WAXD) results showed that the co-PI fibers prepared by dry-jet wet spinning exhibited highly oriented structure along the fiber direction along with a low degree of lateral packing order in the transverse direction. Small-angle X-ray scattering (SAXS) revealed that the radius, length, misorientation and internal surface roughness of the microvoids in the co-PI fibers prepared by the dry-jet wet spinning are lower than those in co-PI fibers prepared by wet spinning. Moreover, the effect of air layer height, as well as the heat treatment on the structure and properties of fibers during the dry-jet wet spinning process, was also studied. The tensile strength and modulus of co-PI fibers prepared by dry-jet wet spinning reached 2.72 GPa and 114.29 GPa, respectively, with an air layer height of 10 mm and a heat stretching temperature of 440°C.

Three azine oligomeric esters were synthesized, characterized by IR, UV, ¹H, ¹³C{¹H} and GPC technique, and applied to chemosensor application. The sensitivity response of the oligomers towards the metal ion was evaluated for a metal ion series. The results have shown selective and sensitive “turn off” fluorescence response towards Fe³⁺ ion in DMF/H₂O (1:1, pH: 7.4, fluorophore: 5 μM) solution. The binding stoichiometry and binding constant of the fluorophores were calculated using the Stern–Volmer equation and Benesi–Hildebrand plots, respectively. The quenching of fluorophores on the addition of Fe³⁺ ion indicates the capability of fluorophore towards quantitative analysis of Fe³⁺. The dimer of oligomers was theoretically studied using DFT, B3LYP/6-311G level basic set to support and explain the quenching mechanism of LMCT, PET process and to explain the DC, AC electrical studies results. The electrical conductivity measurements of solid-state, I₂ doped and undoped oligomers were carried out and the conductivity gradually increases with increase in iodine vapor contact time of oligomers. The electrical conductivity was related with band gap and charge density values of imine nitrogen obtained by Huckel calculations. The dielectric measurements at different temperatures and frequencies were made by two probe method. Among the oligomers, EBHAP has recorded a high dielectric constant at the low applied frequency of 50 Hz at 373 K due to loosely attached π bonds resulting good polarization.

The development of fused filament fabrication has extended the range of application of additive manufacturing in various areas of research. However, the mechanical strength of the fused filament fabrication–printed parts were considerably lower than that of parts fabricated by other conventional methods, owing to the observed anisotropic behaviour and formation of voids by weak interlayer diffusion. Intense studies on the effect of design and process parameters of the printed parts on the mechanical properties have been done, whereas studies on the effect of build orientations and raster patterns needs special concern. The main aim of this work is to fabricate parts printed using quasi-isotropic laminate arrangement of rasters, achieved by a raster layup of [45/0/−45/90]_s, and to compare their mechanical properties with those of the commonly used 0°/90° (cross) and 45°/−45° (crisscross) raster oriented parts. The quasi-isotropic–oriented samples were observed with improved mechanical behaviour in tensile, compressive, flexural and impact tests compared to the commonly employed raster orientations.

In order to expand the application of phenolic-type phthalonitrile resin in high-temperature fields, a series of organic–inorganic hybrid materials have been prepared via conventional blending and doping method. The chemical transformations were monitored by various measurements, while the curing behavior was evaluated by differential scanning calorimetry (DSC), and these new blends could be also cured under auto-catalytic process. The onset polymerization exothermic temperature shifted to lower temperatures (195.3°C). Later, the compatibility within the cured products was analyzed by using energy dispersive spectrometer (EDS) and scanning electron microscope (SEM), where no phase separation occurred between the ceramic domain and the phthalonitrile polymer. Upon curing, the thermal properties of the polymers were characterized by dynamic thermomechanical analysis (DMA) and thermogravimetric analysis (TGA), where enhanced heat resistance and thermal stability were discovered, The blends residual weight (C_y) value was 57.6% with 15 wt.% SiBCN at 1000°C. And when blended with SiBCN precursor, no peak or onset point could be observed in the temperature range (50 to 500°C), which indicated the glass transition temperature greater than 500°C. Additionally, the dielectric properties were evaluated. And when the content was 5 wt.%, the blends dielectric loss was 0.0043 and the permittivity was 4.31. The above results indicated that the introduction of ceramic precursors could enhance the thermal performance of phthalonitrile polymers, consequently the hybrid materials shown great potential in the application of higher temperature fields.

Designing novel low-melting, high-rigidity phthalonitrile resin is of great significance in the current context of development. In this study, rigid spirocycle acetal structure was introduced into phthalonitrile to reduce the melting point and maintain their thermal stability. The chemical structure of resins was confirmed by nuclear magnetic resonance (NMR) spectrometry, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry and Fourier-transform infrared (FTIR) spectroscopy. The curing behaviors were studied by differential scanning calorimetry (DSC). Thermal stability and mechanical properties of the cured resins were investigated by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The processability was studied by rheological analysis. The results indicated the three monomers had a low melting temperature, wide processing windows and low viscosities. These polymers did not exhibit T_g from room temperature to 400°C, exhibited superb dynamic mechanical property and thermal stability.