Modified Bismaleimide Resin Research Articles

Preparation and characterization of a novel allyl ether naphthalene phenolic modified bismaleimide resin and its composites

AbstractAllyl ether naphthol resin (ANPF) was synthesized by introducing 1,5‐dihydroxynaphthalene and 2,7‐dihydroxynaphthalene into phenolic resin and was copolymerized with 4,4′‐bismaleimidodiphenylmethane resin (BDM) to obtain allyl ether naphthol‐modified bismaleimide resins (15‐ANPF‐BDM and 27‐ANPF‐BDM). The resulting thermal stability and glass transition temperature (Tg) were explored by thermogravimetric and dynamic mechanical analyses. The char yield of 15‐ANPF‐BDM at a temperature of 800°C was 46.0%. Additionally, the Tg of 15‐ANPF‐BDM was measured as 311°C, which is an increase of 44°C compared to that of c. The mechanical properties of the ANPF‐BDM/quartz fiber (Qf) composites were also investigated. The results reveal that ANPF‐BDM/Qf composites exhibit similar mechanical strength to APF‐BDM/Qf composites at room temperature. In addition, the mechanical properties of the ANPF‐BDM/ Qf composites demonstrated significant improvement in mechanical properties retained significantly improved at 200°C, with a 68% flexural strength retention and a 96% interlaminar shear retention of 15‐ANPF‐BDM/Qf composites. Thus, ANPF‐BDM/Qf composites exhibit outstanding mechanical properties at 200°C.

Design of high-performance resin by tuning cross-linked network topology to improve CF/bismaleimide composite compressive properties

One effective method for addressing the imbalance between the compression-to-tensile strength ratio in carbon fiber reinforced polymer (CFRP) composites is to create a high-performance resin matrix. We have introduced a bottom-up reinforcement strategy for CFRP composites that involves modifying the bismaleimide resin matrix through the design of its molecular structure. This research utilized the Wittig olefination reaction to convert the polar carbonyl on the bismaleimide monomer to allyl, which resulted in a change in the cross-linked network topology of the bismaleimide resin matrix, and achieved a significant increase in mechanical properties. The tensile modulus of the modified bismaleimide resin matrix reached 5.59 GPa and the mechanism behind this enhancement is discussed in detail. This work is particularly significant due to the preparation and performance evaluation of CF/bismaleimide composites. The compressive strength and interlaminar shear strength of CF/bismaleimide composites showed noticeable improvements of 30.08% and 22.23% respectively, indicating that increasing the modulus of the resin matrix is an effective strategy for enhancing the compressive and interfacial properties of the composite material. Our work aims to offer research insights and design ideas for future exploration of bismaleimide resins in advanced composite resin matrices.

Characterization of Mechanical, Electrical and Thermal Properties of Bismaleimide Resins Based on Different Branched Structures.

Bismaleimide (BMI) resin is an excellent performance resin, mainly due to its resistance to the effect of heat and its insulating properties. However, its lack of toughness as a cured product hampers its application in printed circuit boards (PCBs). Herein, a branched structure via Michael addition was introduced to a BMI system to reinforce its toughness. Compared with a pure BMI sample, the flexural strength of the modified BMI was enhanced, and its maximum value of 189 MPa increased by 216%. The flexural modulus of the cured sample reached 5.2 GPa. Using a scanning electron microscope, the fracture surfaces of BMI samples and a transition from brittle fracture to ductile fracture were observed. Furthermore, both the dielectric constant and the dielectric loss of the cured resin decreased. The breakdown field strength was raised to 37.8 kV/mm and the volume resistivity was improved to varying degrees. Consequently, the resulting modified BMI resin has the potential for wide application in high-frequency and low-dielectric resin substrates, and the modified BMI resin with a structure including three different diamines can meet the needs of various applications.

Synthesis of a Novel Hyperbranched Polyimide for Reinforcing Toughness and Insulating Properties of Bismaleimide Resin.

Bismaleimide (BMI) resin has great potential in aerospace, electronic, and machinery fields due to its extraordinary thermal stability. Owing to BMI’s lower impact strength, various modified BMI resins have been prepared using CTBN, PEEK, fillers, and hyperbranched polymer to achieve higher impact strength. However, enhancement of toughness causes deterioration of other performance, such as Tg, thermal stability, and brittleness. In this work, BMI resin modified by hyperbranched polyimide (HBPI) was obtained. HBPI designed with flexible segments, unsaturated bonds, and a low degree of branching was synthesized. FT-IR and 13C-NMR were applied to confirm the successful fabrication of HBPI. The mechanical strength and dielectric properties of cured BMI resin containing various levels of HBPI were analyzed systematically. The impact and bending strength were improved significantly with increased HBPI content. When the content of HBPI is 40 wt.%, the impact strength and bending strength reach the maximum value of 32 kJ/mm and 88 MPa. In addition, the BMI cured with HBPI exhibits enhanced bending modulus to the value of 5.9 GPa. Furthermore, the dielectric strength of cured resin was improved to 28.3 kV/mm. The improved mechanical strength and enhanced dielectric properties are attributed to the increasing free volume induced by HBPI. These results indicate the promise of BMI resin modified by HBPI applied in insulating coatings and low dielectric laminates used in high frequency.

High temperature and toughened bismaleimide structural film adhesive for high performance CFRP bonding over 300 °C

Structural adhesive play an important role in the manufacturing of composite structures. Here, a high-temperature resistant bismaleimide (BMI) structural film adhesive was prepared by using a chemically modified BMI resin as the matrix with poly(phthalazinone ether nitrile ketone) (PPENK) as the film-forming agent. The toughness of the adhesive was greatly enhanced by adding vinyl-terminated butadiene acrylonitrile (VTBN). The performance of the high-temperature resistant BMI structural film adhesive was optimized with 15 phr of PPENK and 6 phr of VTBN, which exhibits outstanding heat resistance, excellent bonding and peeling performance. Its glass transition temperature is as high as 272 °C while maintaining the shear strength of 10.8 MPa at 316 °C. The synergistic toughening effects of VTBN and PPENK significantly improve the toughness with a high peel strength of 41.7 N mm/mm. The co-cured composite joint formed between BMI prepregs and modified BMI adhesive exhibits shear strength of 10.7 MPa at 316 °C and peel strength of 21.8 N mm/mm, indicating an effective bonding between the modified BMI adhesive and BMI prepreg. The phase at the bonding interface is proved to be an important factor for high-performance at the bonding joint.

Curing kinetics, thermal and erosive wear characteristics of bismaleimide blends modified by polyaryletherketone

The work aimed to study the effect of thermoplastic polyaryletherketone (PAEK) on the curing kinetics, thermal stability and erosive wear performances of bismaleimide (BMI) resin blends. Toughened bismaleimide blends were fabricated using the allyl compound modified bismaleimide resin prepolymer as matrix and PAEK as a toughening agent by blending method. The modified PAEK/BMI blends were characterized and analyzed using the fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), the swirling water jet erosive wear apparatus, scanning electron microscope (SEM) and three-dimensional surface profilometer. No obvious glass transition was observed for PAEK modified BMI blends in the temperature range of 50–350°C. In addition, the char yields ( Yc) and the heat-resistance index ( THRI) of the PAEK/BMI blends were affected by PAEK addition. The kinetic parameters, such as the activation energy and the pre-exponential factor of the PAEK/BMI blends were also higher than that of unmodified BMI blends, indicating that the incorporation of PAEK could promote the curing reaction of the epoxy resin without changing the curing mechanism. The erosive wear rate increased with the addition of PAEK especially when the mass fraction of PAEK was 10 parts per hundred of resins ( phr.). These results suggested that the thermal stability of the PAEK/BMI blends was significantly enhanced while the erosive wear resistance decreased by introducing the PAEK.

Low‐temperature processable glass fiber reinforced aromatic diamine chain extended bismaleimide composites with improved mechanical properties

AbstractThe synthesis of 4,4′‐bismaleimido diphenylmethane (BMIM) and modified BMIM by its chain extension using commercially available aromatic diamines like 4,4′‐diamino diphenyl methane (DDM), 4,4′‐diaminodiphenyl sulphone (DDS), and 4,4′‐diamine diphenyl ether (DDE) was done. The synthesized materials have been characterized for structural aspects using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The structure of BMIM was confirmed due to the presence of specific bands at ~1400 and 1705 cm−1 responsible for CC and OCNCO groups, respectively. The reduction in the heat of fusion and enthalpy of curing for chain extended bismaleimides/modified BMIM shows the influence of the swivel group in diamine during curing. The curing window has broadened for BMIM_M and BMIM_E by ~40°C and narrowed for BMIM_S by ~100°C. The mechanical properties and the chemical resistance were studied for the composites made from the BMIM and modified BMIM based composites. Fiber‐enhanced modified bismaleimide resin has improved mechanical properties.

Enhanced toughness and lowered dielectric loss of reactive POSS modified bismaleimide resin as well as the silica fiber reinforced composites

AbstractInherent brittleness is the most weakness of bismaleimide resin, which adversely affects the performance and application of the terminal fiber reinforced bismaleimide composites. In this study, polyhedral oligomeric silsesquioxane (POSS) with glycidyl group (G‐POSS) and methacryloxy propyl group (MA‐POSS) are utilized to toughen diallyl bisphenol‐A/N, N′‐4,4′‐diphenylmethane bismaleimide (BD resin) to obtain hybrid resins named BDGP and BDMP. The results of hybrid resins show that the two series hybrid resins perform higher toughness, strength, water resistance as well as lower dielectric constant and loss comparing with pristine BD resin, and BDMP perform better than BDGP due to that MA‐POSS can react with BD resin while G‐POSS cannot. In specific, the BDMP3 in which 3 wt% MA‐POSS is added performs the highest impact strength of 19.0 KJ/m2, increased by 102.1% comparing with pristine BD resin, and it also performs the lowest dielectric constant of 3.04 as well as lowest dielectric loss of 0.006 at 1 MHz. In addition, the silica fiber reinforced BDMP composites (SF/BDMP) are fabricated, and the results show that the bending strength and interlaminar shear strength of SF/BDMP3 composite are enhanced to 290.2 and 32.5 MPa, 32.0% and 38.4% higher than those of SF/BD composite, and the corresponding dielectric loss (0.025) at 8.2 GHz is reduced by 45.9%. This research displays that reactive POSS can improve the toughness and reduce the dielectric loss of resin, which is benefit to obtain a high performance and functional resin‐based composites with excellent mechanical properties and low dielectric properties.

Graphene Nanoplatelets Hybrid Flame Retardant Containing Ionic Liquid and Ammonium Polyphosphate for Modified Bismaleimide Resin: Excellent Flame Retardancy, Thermal Stability, Water Resistance and Unique Dielectric Properties.

To achieve the requirements of modified bismaleimide resin composites in electronic industry and high energy storage devices, flame retardancy, water resistance and dielectric properties must be improved. Hence, a highly efficient multifunctional graphene nanoplatelets hybrid flame retardant is prepared by ionic liquid graphite and ammonium polyphosphate. The preparation processes of the flame retardants are simple, low energy consumption and follow the green chemical concept of 100% utilization of raw materials, compared with chemical stripping. The bismaleimide resin containing 10 wt.% of the flame retardant show good flame retardancy, resulting in the limiting oxygen index increases to above 43%, and the peak heat release rate, total heat release and total smoke release decrease by 41.8%, 47.8% and 52.3%, respectively. After soaking, mass loss percentage of the modified bismaleimide resin only decreases by 0.96%, the dielectric constant of the composite increases by 39.4%, and the dielectric loss decreases with the increase of frequency. The hybrid flame retardants show multifunctional effect in the modified bismaleimide resin, due to the physical barrier, the chemical char-formation, hydrophobicity and strong conductivity attributed to co-work of Graphene nanoplatelets, ammonium polyphosphate and ionic liquid.

Bismaleimide resins modified by an allyl ether of bio-based resveratrol with excellent halogen-free and phosphorus-free intrinsic flame retardancy and ultrahigh glass transition temperature

Development of new allyl compounds to modify bismaleimide (BMI) resins for improving the toughness while maintaining a high thermal performance and flame retardancy is still urgent. In this study, we synthesized the allyl ether of resveratrol (AER), a bio-based allyl compound, to modify BMI resin. A series of BMI/AER resins (BA resins) were prepared by changing the molar ratio of BMI to AER. Compared with 2,2′-diallyl bisphenol A (DBA) modified BMI resins (BD resins), which has been widely used in industry, BA resins can be cured at a lower temperature. Although the toughness of cured BA resins was slightly inferior than that of cured BD resins, the cured BA resins exhibited much superior thermal performance and flame retardancy to the cured BD resins. For the BA-0.8 resin with a molar ratio of imide to allyl groups of 1:0.8, the glass transition temperature, thermal decomposition temperature of 5% weight loss, and char yield of the cured product were as high as 388 °C, 415 °C, and 48.6%, respectively. Meanwhile, the UL-94 and limit oxygen index (LOI) tests revealed an excellent flame retardancy of the cured BA-0.8 resin with V-0 level and LOI of 37.7%. The remarkable properties were attributed to AER with the tri-functionality and stiffness conjugated stilbene backbone giving the cured resins higher crosslinking density, chain rigidity and thermostability compared with DBA. This work provides a novel insight into the development of high-performance bismaleimide-based thermosetting resins with excellent halogen-free and phosphorus-free intrinsic flame retardancy.

Preparation and properties of bismaleimide resin blended with alkynyl-terminated modifiers

A kind of modified bismaleimide resin, with good processability, heat resistance, and impact strength was developed, using 4,4′-dipropargyloxydiphenyl ether (DPEDPE), N-(4-propargyloxyphenyl)maleimide (4-PPM), and 3-ethynylphenyl maleimide (3-EPM) as modifiers. The DPEDPE, 4-PPM, and 3-EPM were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and 1H-nuclear magnetic resonance (1H NMR), and used to modify the N,N′-(4,4′-diphenylmethane)bismaleimide (BDM)/2,2′-diallyl bisphenol A (DABPA) resin system (BD) to obtain the different blend resin systems of DPEDPE-modified BD (BDD), 4-PPM-modified BD (BDP), and 3-EPM-modified BD (BDE). The curing temperature of BD resin increases with increase of the alkynyl-terminated modifier content. The processability of BD resin was improved with addition of the propargyloxy-terminated compounds. The temperature of 5% weight loss, residual yield at 800°C and glass transition temperature of the cured BD resin increase with increase of the alkynyl-terminated modifier content and can reach 443°C, 46.7% and higher than 380°C. The tensile strength of the cured BD resin decreases with increase of alkynyl-terminated modifier content. The impact strength of the cured BD resin increases with increase of the propargyloxy-terminated compound content and can increase by 65%. The tensile strength, elastic modulus, and impact strength of the cured BD resin blended with DPEDPE can be 73.7 MPa, 4.1 GPa, and 19.6 kJ m−2, respectively. Moreover, the cured BD resin blended with DPEDPE has good water absorption resistance.

Enhanced toughness and thermal properties of bismaleimide resin based on the synergistic effect of reactive amino‐terminal poly(phthalazinone ether nitrile sulfone) and bisallyl bearing diphenol group

Bismaleimide (BMI) resins have poor toughness due to their high crosslink density, which limits their wide development and application. In this study, the amino‐terminated poly(phthalazinone ether nitrile sulfone) (PPENS‐DA) resin was designed and the curing agent of 3,3′‐diallyl‐4,4′‐biphenol (DABP) was synthesized to toughen N,N′‐(4,4′‐diphenylmethane) bismaleimide (BDM) resin. The impact strength, flexural strength and fracture surface structures of the DABP/BDM and PPENS‐DA/DABP/BDM blends were studied. The results showed that the notched impact strength of the blends with 10‐phr PPENS‐DA is 4.98 kJ/m2, which was 36% higher than that of pristine BDM/DABP blend and 200% higher than that of the 2,2′‐diallyl bisphenol A (DABPA) modified BMI resin system. The glass transition temperature (Tg) has been improved from 247 to 269°C for the blend system as evidenced by DMA. Rheological behavior analysis indicated that the blend system has a broad processing window (90‐175°C) with low viscosity of less than 1 Pa·s and low curing activation energy of 67.2 kJ/mol.

Modified Bismaleimide Resins with Low Dielectric Properties

バイオマスから誘導される低極性長鎖脂肪族ジアミンと3,3′-dimethyl-5,5′-diethyl-4,4′-diphenylmethane bismaleimide (BMI)の反応により，変性BMI (m-BMI)樹脂を合成し，その樹脂硬化物の低誘電特性を含む基本特性を確認した。さらに，m-BMIと低極性であるp,p’-Divinyl-1,2-diphenylethan (BVPE)，1,2,4-Trivinylcyclohexane (TVCH)のブレンドにより樹脂硬化物のガラス転移温度(Tg)を改善した。すなわち，m-BMI (CB12)とBVPEが50:50の樹脂硬化物は，10 GHzでの比誘電率(εr) 2.47，誘電正接(tanδ) 0.0012，Tg: 206°Cを示し，m-BMI (CB13)とTVCHが50:50からなる樹脂硬化物は，εr: 2.53，tanδ: 0.0017，Tg: 204°Cを示した。 変性BMI (m-BMI)の短所を低減し，樹脂硬化物に低誘電，高耐熱性という特性を与えることで，5G通信関連エレクトロニクス実装用高分子材料に要求される性能を示すことが確認された。

Bio‐based hydroxymethylated eugenol modified bismaleimide resin and its high‐temperature composites

AbstractHydroxymethylated eugenol (MEG) and poly (hydroxymethylated eugenol) (PMEG) were synthesized by the condensation reaction of eugenol (EG) with formaldehyde. The different contents of MEG and PMEG were used to modify 4,4′‐bismaleimidediphenylmethane (BMI). The cured MEG‐BMI resins exhibit good thermal stability evidenced by its 5% weight loss temperatures above 407°C and its residue above 39.4% at 800°C under nitrogen. For carbon/MEG‐BMI composites, their glass transition temperatures were around 400°C; their flexural strength and moduli were maintained at a range of 488.87–575.47 MPa and 48.84–60.26 GPa, respectively. With the increasing content of BMI in the resin formulation, the flexural properties decreased; comprehensively the composite with the eugenol/maleimide unit ratio (1:0.3 mol) had the best mechanical and thermal properties, meanwhile its renewable carbon content was as high as 57.80%. As a new candidate of high temperature thermosetting resin, MEG would find promising applications for advanced composites' matrice.

Optimization and preparation of an allyl phenoxy-modified bismaleimide resin

A thermosetting resin system has been developed by the copolymerization of allyl phenoxy, bismaleimide (BMI), and diallyl bisphenol A and optimized using response surface methodology. An optimized modified resin system with enhanced properties was achieved based on empirical second-order models expressing the relationship between the modifier contents and the mechanical properties. Dicumyl peroxide (DCP) was selected as initiator to further improve the curing behavior and mechanical properties of the optimized resin system. The effect of initiator contents on impact, flexural strength, and heat distortion temperature was also investigated. The curing behavior, morphology, and thermal stability of the optimized resin were carefully characterized using differential scanning calorimeter, scanning electron microscope, and thermogravimetric and dynamic mechanical analyzers, respectively. For evaluating the efficiency of modified BMI resin system, laminated composites using glass fiber cloth were fabricated using a hot press and tested for mechanical properties. The results showed that the DCP reduced the curing temperature significantly, improved the curing process, and proved to be very effective in heat resistance. Meanwhile, the laminated composite with initiator showed 13–27% higher mechanical properties and 5–7% higher retention rate at high temperature when compared with the neat resin composite system. The optimized resin system with higher mechanical properties, good heat resistance, and better manufacturability can be used as matrix resin for making advanced fiber-reinforced composites.

Novel Bismaleimide Resins Modified by Allyl Compound Containing Liquid Crystalline Structure

ABSTRACTA novel allyl compound containing liquid crystalline structure, i.e., 4,4’‐bis(4‐allyloxy benzoic acid) phenyl ester (BAOBE), was synthesized. The chemical structure of BAOBE was characterized by Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectra, and the liquid crystalline properties were confirmed by polarized optical microscopy (POM). Besides, a series of modified bismaleimide (BMI) resins were prepared based on N,N′‐4,4′‐bismaleimidodiphenylmethylene (BDM), BAOBE, and O,O’‐diallyl bisphenol A (DABPA). The results of thermogravimetric analysis (TGA) indicate that the modified resins have excellent thermal stability with the highest temperatures for 5% weight loss above 438°C. The results of dynamic mechanical analysis (DMA) suggest that the glass transition temperature (Tg) of the modified resins are above 280°C. Besides, the introduction of BAOBE leads to a significant improvement in the flexural and impact properties of the modified BMI resins. Compared with the resin with only DABPA as a modifier, the highest flexural and impact strength can reach 156.2 MPa and 15.6 kJ/m2, increased by 19.2% and 90.2%, respectively.

Fabrication of modified bismaleimide resins by hyperbranched phenyl polysiloxane and improvement of their thermal conductivities

Synthetic terminal amine group hyperbranched phenyl polysiloxane (NH2-HBPSi) is introduced into a bismaleimide/diallylbisphenol A (BMI/DABA) prepolymer to fabricate NH2-HBPSi/BMI/DABA resins.

Fabrication and origin of new flame retarding bismaleimide resin system with low dielectric constant and loss based on microencapsulated hexaphenoxycyclotriphosphazene in low phosphorus content

To maintain sustainable development, developing new and effective phosphorus flame retardants that can simultaneously endow thermally resistant thermosetting resins with outstanding flame retardancy and dielectric properties is a great but worthy challenge. A new flame retardant coded as MH, polyamide microencapsulated hexaphenoxycyclotriphosphazene (HPCTP), was synthesized through interfacial polymerization. The influences of main synthesis parameters on the morphology and thermal stability were discussed. Furthermore, a new kind of modified bismaleimide resins (MH/BD) were prepared by incorporating MH into 4, 4' – bismaleimidodiphenylmethane/o, o’-diallylbisphenol A (BD) resin, and the structure and performances of MH/BD resins were studied and compared with those of HPCTP/BD resins. Results show that the MH/BD resin, of which the content of phosphorus is as small as only 0.33 wt%, has outstanding flame retardancy, mainly reflected by high limiting oxygen index (LOI), low total heat evolved and total smoke production; while the content of phosphorus in the HPCTP/BD resins should be higher than 1.30 wt% to get similar flame retardancy. Moreover, when the contents of MH and HPCTP are the same, the MH/BD resins exhibit lower dielectric constant and loss over the wide frequency from 102 to 104 Hz than HPCTP/BD resins, suggesting that the former is more attractive to be used in applications related with electric and electronic fields. The mechanisms behind these attractive performances were intensively discussed. The interaction between core and shell of MH and the effect of MH on the crosslinked structure of cured resins are responsible for these attractive properties. The research reported herein provides a new method and origin to prepare effective phosphorus flame retardant and related high performance flame retardant resins.

Green flame retarding bismaleimide resin with simultaneously good processing characteristics, high toughness and outstanding thermal stability based on a multi-functional organic boron compound

Multi-function and green are two keywords of developing new flame retarding thermosetting resins, however, to achieve this target is still a big challenging today. Herein, a new kind of flame retarding bismaleimide resins with simultaneously good processing characteristics, high toughness and outstanding thermal stability were prepared by copolymerizing 4,4′-bismaleimidodiphenylmethane (BDM) with allyl triphenylborate (ATPB). The structure and integrated performances of BDM/ATPB resins were systematically studied and compared with the BDM/o,o′-diallylbisphenol A resin (coded as BD) that is almost known to be the best modified bismaleimide resin available. Results show that BDM/ATPB resins are solids with low softening points; they can be dissolved in acetone and have wide processing window, completely overcoming the poor processing characteristics of BDM. The properties of the BDM/ATPB system are dependent on the molar ratio of imide and allyl groups, and BDM/ATPB3 resin of which the molar ratio of imide to allyl groups (1:0.85) is the same as that of BD resin not only has significantly improved flame retardancy, reflected by obviously longer time to ignition, 1.5–3.0 times higher fire performance index, and greatly decreased heat releases, but also has about 10 °C higher initial decomposition temperature in both air and nitrogen atmospheres as well as about 1.2–1.3 times higher impact and flexural strengths, clearly demonstrating that ATPB is a multi-functional and green modifier for bismaleimide. The origin behind these attractive results of BDM/ATPB resins was intensively discussed.

Preparation and properties of modified bismaleimide resins by novel bismaleimide containing 1,3,4‐oxadiazole

Bismaleimide (BMI) resin is a high‐performance thermosetting polymer, but its inherent brittleness hinder a broader range of application. Therefore, it has aroused wide concern to improve the toughness of BMI resins without scarification of their thermal stability. This paper reported some studies on modified BMI resins based on diallyl bisphenol A, novel BMI monomers, e.g. 2‐[3‐(4‐maleimidophenoxy)phenyl]‐5‐(4‐maleimidophenyl)‐1,3,4‐oxadiazole (m‐Mioxd) or 2‐[4‐(4‐maleimidophenoxy)phenyl]‐5‐(4‐maleimidophenyl)‐1,3,4‐ oxadiazole (p‐Mioxd) in different proportions (0.87:1, 1:1, 1.2:1; mol/mol). The curing mechanism and kinetics of the copolymerized systems were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy. Thermogravimetric analysis was applied to study the thermal properties of the cured resins, and the results indicated that the modified resins had excellent thermal stability with high residual weight percentage at 700°C (>50%), temperatures for 5% weight loss around 400°C. Besides, N,N′‐4,4′‐bismaleimidodiphenylmethylene and O,O′‐diallyl bisphenol A resin blends were modified by m‐Mioxd and p‐Mioxd, respectively. We investigated the effects of mole concentration of m‐Mioxd or p‐Mioxd on the curing process, mechanical properties, fracture toughness, and heat resistance of the modified resins. The results revealed that the introduction of m‐Mioxd and p‐Mioxd could improve the impact property of the modified BMI resins. When their proportion was 0.07, the impact strength increased 123.8% and 108.3%, respectively. The novel chain‐extended BMIs could reduce the crosslink density of cured resins and improve the brittleness effectively. Copyright © 2015 John Wiley & Sons, Ltd.