Synthesis and characterization of bisitaconimides. I

This article describes the synthesis and characterization of bisitaconimides on the basis of 4,4′‐diaminodiphenylether, 2,2′‐bis[4‐(4‐aminophenoxy)phenyl]propane, 1,3‐bis(4‐aminophenoxy)benzene, and 1,4‐bis (4‐aminophenoxy)benzene. Isomerization of the itaconimides to citraconimides (varying in the range of 25–40%) was observed during synthesis. The curing exotherm and thermal stability of the cured resins depended on the backbone structure of itaconimides. The curing exotherm immediately followed the melting endotherms. These resins cured at lower temperatures than bismaleimides but thermal stability of cured bismaleimides was higher than bisitaconimides. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2277–2282, 2002     

Synthesis of novel phosphorous‐containing biphenol, 2‐(5, 5‐dimethyl‐4‐phenyl‐2‐oxy‐1,3,2‐dioxaphosphorin‐6‐yl)‐1,4‐benzenediol and its application as flame‐retardant in epoxy resin

A novel phosphorous‐containing biphenol, 2‐(5,5‐dimethyl‐4‐phenyl‐2‐oxy‐1,3,2‐dioxaphosphorin‐6‐yl)‐ 1,4‐benzenediol (DPODB), was prepared by the addition reaction between 5,5‐dimethyl‐4‐phenyl‐2‐oxy‐1,3,2‐dioxaphosphorinane phosphonate (DPODP) and p‐benzoquinone (BQ). The compound (DPODB) was used as a reactive flame retardant in o‐cresol formaldehyde novolac epoxy resin (CNE) for electronic application. The structure of DPODB was confirmed by FTIR and NMR spectra. Thermal properties of cured epoxy resin were studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The flame retardancy of cured epoxy resins was tested by UL‐94 vertical test and achieved UL‐94 vertical tests of V‐0 grade (nonflammable). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3842–3847, 2006     

Synthesis and properties of novel 4,4′‐biphenylene‐bridged flame‐retardant cyanate ester resin

The bisphenol‐containing 4,4′‐biphenylene moiety was prepared by the reaction of 4,4′‐bis(methoxymethyl) biphenyl with phenol in the presence of p‐toluenesulfonic acid. The bisphenol was end‐capped with the cyanate moiety by reacting with cyanogen chloride and triethylamine in dichloromethane. Their structures were confirmed by Fourier transform infrared spectroscopy, ¹H‐NMR, and elemental analysis. Thermal behaviors of cured resin were studied by differential scanning calorimetry, dynamic mechanical analysis, and TGA. The flame retardancy of cured resin was evaluated by limiting oxygen index (LOI) and vertical burning test (UL‐94 test). Because of the incorporation of rigid 4,4′‐biphenylene moiety, the cyanate ester (CE) resin shows good thermal stability (T_g is 256°C, the 5% degradation temperature is 442°C, and char yield at 800°C is 64.4%). The LOI value of the CE resin is 42.5, and the UL‐94 rating reaches V‐0. Moreover, the CE resin shows excellent dielectric property (dielectric constant, 2.94 at 1 GHz and loss dissipation factor, 0.0037 at 1 GHz) and water resistance (1.08% immersed at boiling water for 100 h). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of epoxy‐functionalized hyperbranched poly(phenylene oxide) and its modification of cyanate ester resin

High curing temperature is the key drawback of present heat resistant thermosetting resins. A novel epoxy‐functionalized hyperbranched poly(phenylene oxide), coded as eHBPPO, was synthesized, and used to modify 2,2′‐bis (4‐cyanatophenyl) isopropylidene (CE). Compared with CE, CE/eHBPPO system has significantly decreased curing temperature owing to the different curing mechanism. Based on this results, cured CE/eHBPPO resins without postcuring process, and cured CE resin postcured at 230°C were prepared, their dynamic mechanical and dielectric properties were systematically investigated. Results show that cured CE/eHBPPO resins not only have excellent stability in dielectric properties over a wide frequency range (1–10⁹Hz), but also show attractively lower dielectric constant and loss than CE resin. In addition, cured CE/eHBPPO resins also have high glass transition temperature and storage moduli in glassy state. These attractive integrated performance of CE/eHBPPO suggest a new method to develop high performance resins. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Properties and origins of high‐performance poly(phenylene oxide)/cyanate ester resins for high‐frequency copper‐clad laminates

A high‐performance matrix is the key base for the fabrication of high‐frequency copper‐clad laminates. A high‐performance resin system based on commercial poly(phenylene oxide) (PPO) and 2,2′‐bis(4‐cyanatophenyl) isopropylidene (BADCy), coded as PPO‐n/BADCy (where n is the weight parts of PPO per 100 weight parts of BADCy), was developed. The effect of PPO on the key properties, including the dielectric and thermal properties, water resistance, and toughness, of the cured resins was investigated extensively. The results show that PPO not only catalyzed the curing reaction of BADCy but also reacted with BADCy to form a single‐phase structure. Furthermore, compared with the cured BADCy resin with 1 phr epoxy resin as a catalyst, the cured PPO‐n/BADCy resins had significantly increased impact strengths and decreased dielectric constants, loss, and water resistance. The reasons behind these desirable improvements are discussed from the view of structure–property relationships. These results suggest that the PPO‐n/BADCy system has great potential to be used as a matrix for high‐frequency copper‐clad laminates or other advanced composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane/epoxy/glass fiber composites

Bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane was prepared by treating CNBr with bis(4‐hydroxy‐3,5‐dimethylphenyl)anisylmethane and blended with commercial epoxy resin in different ratios and cured at 120°C for 2 h, 180°C for 1 h, and postcured at 220°C for 1 h using diamino diphenyl methane as curing agent. Castings of neat resin and blends were prepared and characterized. The composite laminates were also fabricated with glass fiber using the same composition. The tensile strength of the composites increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m², for neat epoxy resin, to 0.8615 kJ/m², for 9% cyanate ester‐modified epoxy system. The 10% weight loss temperature of pure epoxy (358°C) was increased to 390°C by the incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% in the epoxy resin increases the T_g from 143 to 147°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of bis(4‐cyanato 3,5‐dimethylphenyl) naphthyl methane/epoxy/glass fiber composites

Bis(4‐cyanato 3,5‐dimethylphenyl) naphthylmethane was prepared by treating CNBr with bis(4‐hydroxy 3,5‐dimethylphenyl) naphthylmethane in the presence of triethylamine at −5 to 5°C. The dicyanate was characterized by FT‐IR and NMR techniques. The prepared dicyanate was blended with commercial epoxy resin in different ratios and cured at 120°C for 1 hr, 180°C for 1 hr, and post cured at 220°C for 1 hr using diamino diphenyl methane (DDM) as curing agent. Castings of neat resin and blends were prepared and characterized by FT‐IR technique. The morphology of the blends was evaluated by SEM analysis. The composite laminates were also fabricated from the same composition using glass fiber. The mechanical properties like tensile strength, flexural strength, and fracture toughness were measured as per ASTMD 3039, D 790, and D 5528, respectively. The tensile strength increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m² for neat epoxy resin to 0.8615 kJ/m² for 9% cyanate ester epoxy modified system. The thermal properties were also studied. The 10% weight loss temperature of pure epoxy is 358°C and it increased to 398°C with incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% loading level does not affect the T_g to a very great extent. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Preparation and characterization of unsaturated poly(ester‐imide) based on 1,4‐bis[2′‐trifluoromethyl‐4′‐(4″‐glycolformate)‐trimellitimidophenoxy]benzene

A novel diimidodialcohol monomer, 1,4‐bis[2′‐trifluoromethyl‐4′‐(4″‐glycolformate)‐ trimellitimidophenoxy]benzene (BGTB), was synthesized and characterized. It was reacted with isophthalic acid, maleic anhydride and propylene glycol to produce a novel unsaturated poly(ester‐imide) (BGTB‐UPEI) with imide and trifluoromethyl groups in the polymer backbone. The BGTB‐UPEI resin was diluted with reactive monomer (styrene) to give a low‐viscous poly(ester‐imide)/styrene (BGTB‐UPEI/St) mixed solution, which was then thermally cured to yield thermosetting BGTB‐UPEI/St composite. The effect of processing parameters such as the curing temperature and curing time, reactive monomer concentration and initiator amount on the curing reaction was systematically investigated. Experimental results indicated that the thermally cured BGTB‐UPEI/St composite exhibited much better thermal, mechanical, electrical insulating properties and chemical resistance than the standard unsaturated polyester/polystyrene composite. Copyright © 2006 Society of Chemical Industry     

Synthesis and characterization of novel chain‐extended bismaleimides containing fluorenyl cardo structure

Novel fluorenyl cardo chain‐extended bismaleimides (FCCEBMIs) were synthesized by reacting maleic anhydride with fluorenyl cardo diamine and different dianhydrides. FCCEBMIs were characterized by FT‐IR spectra (FT‐IR), ¹H NMR, and elemental analysis. All FCCEBMI monomers were readily soluble in a variety of organic solvents, such as N‐methyl‐2‐pyrrolidinone, N,N‐dimethyl acetamide, chloroform (CHCl₃), methylene chloride (CH₂Cl₂), dimethyl sulfoxide, and tetrahydrofuran when compared with 9,9‐bis(4‐maleimidophenyl) fluorene. Curing process was investigated by differential scanning calorimetry. Thermal properties of the cured FCCEBMIs were characterized by thermogravimetry analysis, the cured products are stable up to 430°C. The results show that the FCCEBMIs with imide structure improve significantly the solubility of bismaleimide (BMI) in organic solvents without sacrificing thermal properties of cured BMIs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of methyl hexahydrophthalic anhydride‐cured fluorinated epoxy resin 2,2‐bisphenol hexafluoropropane diglycidyl ether

The fluorinated epoxy resin, 2,2‐bisphenol hexafluoropropane diglycidyl ether (DGEBHF) was synthesized through a two‐step procedure, and the chemical structure was confirmed by ¹H n uclear magnetic resonance (NMR), ¹³C NMR, and Fourier transform infrared (FTIR) spectra. Moreover, DGEBHF was thermally cured with methyl hexahydrophthalic anhydride (MHHPA). The results clearly indicated that the cured DGEBHF/MHHPA exhibited higher glass transition temperature (T_g 147°C) and thermal decomposition temperature at 5% weight loss (T₅ 372°C) than those (T_g 131.2°C; T₅ 362°C) of diglycidyl ether of bisphenol A (DGEBA)/MHHPA. In addition, the incorporation of bis‐trifluoromethyl groups led to enhanced dielectric properties with lower dielectric constant (D_k 2.93) of DGEBHF/MHHPA compared with cured DGEBA resins (D_k 3.25). The cured fluorinated epoxy resin also gave lower water absorption measured in two methods relative to its nonfluorinated counterparts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2801–2808, 2013     

Preparation of poly(1,4‐cyclohexylenedimethylene phthalate)s and their use as modifiers for aromatic diamine‐cured epoxy resin

Poly(1,4‐cyclohexylenedimethylene phthalate) s, prepared by the reaction of phthalic anhydride and 1,4‐cyclohexane dimethanol (35/65 or 73/27 mol % cis/trans or trans alone), have been used to improve the toughness of bisphenol‐A diglycidyl ether epoxy resin cured with 4,4′‐diaminodiphenyl sulfone. The aromatic polyesters include poly(cis/trans‐1,4‐cyclohexylenedimethylene phthalate) (PCP) based on a commercial cyclohexanedimethanol, poly(trans‐1,4‐cyclohexylenedimethylene phthalate) (trans‐PCP) and poly(cis/trans‐1,4‐cyclohexylenedimethylene phthalate) (cis‐rich PCP) prepared from a cis‐rich diol. The polyesters used were soluble in the epoxy resin without solvents and were effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt% of PCP (MW 6400 g mol⁻¹) led to an 80% increase in the fracture toughness (K_IC) of the cured resin with no loss of mechanical and thermal properties. The toughening mechanism is discussed in terms of morphological and dynamic viscoelastic behaviours of the modified epoxy resin system. © 2000 Society of Chemical Industry     

Synthesis and properties of bismaleimide resin containing dicyclopentadiene or dipentene. VI

New aromatic bismaleimides (BMIs), bis(4‐maleimidophenoxy‐3,5‐dimethylphenyl)dicyclopentadiene (DCPDBMI) and bis(4‐maleimido‐phenoxy‐3,5‐dimethylphenyl)dipentene (DPBMI), containing a large dicyclopentadiene (DCPD) or dipentene (DP) and aryl ether linkage, were synthesized from diamine bis(4‐aminophenoxy‐3,5‐dimethylphenyl)dicyclopentadiene (DCPDA) or bis(4‐aminophenoxy‐3,5‐dimethylphenyl)dipentene(DPA) and maleic anhydride by the usual two‐step procedure that included ring‐opening addition to give bismaleamic acid, followed by cyclodehydration to bismaleimide. The monomers were characterized by Fourier transform infrared spectroscopy, proton NMR, elemental analyses, and mass spectra. Their thermal polymerization was investigated by DSC. The presence of a large cycloaliphatic moiety in the backbone of the bismaleimide increased the curing temperature and reduced the reactivity of the maleimide bond. Thermal and electrical properties of cured bismaleimide resins were studied using a dielectric analyzer, dynamic mechanical analyzer, and thermal gravimetric analyzer. These data were compared with that of commercial 4,4‐bismaleimidodiphenylmethane (DDMBMI). The cured DCPDBMI or DPBMI exhibits a lower dielectric constant, dissipation factor and moisture absorption than those of DDMBMI. Copyright © 2006 Society of Chemical Industry     

Synthesis,characterization and thermal properties of phenylene–disiloxane polymers obtained from catalytic cross‐dehydrocoupling polymerization of bis(dimethylsilyl)benzene isomers and water

Phenylene–disiloxane polymers were prepared from 1,4‐bis(dimethylsilyl)benzene and 1,3‐bis(dimethylsilyl)benzene with water in various ratios by catalytic cross‐dehydrocoupling polymerization. Each isomer showed almost equal reactivity in the polymerization as verified by the analysis of the composition by ¹H NMR. Crystallinity observed in the polymer obtained from the 1,4‐isomer was removed by incorporating a small amount of 1,3‐isomer. © 2001 Society of Chemical Industry     

Low dielectric thermoset. I. Synthesis and properties of novel 2,6‐dimethyl phenol‐dicyclopentadiene epoxy

A 2,6‐dimethyl phenol‐dicyclopentadiene novolac was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant 2,6‐dimethyl phenol‐dicyclopentadiene novolac was epoxidized to 2,6‐dimethyl phenol‐dicyclopentadiene epoxy. The structures of novolac and epoxy were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis, mass spectroscopy (MS), nuclear magnetic resonance spectroscopy (NMR), and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol‐dicyclopentadiene epoxy was then cured with 4,4‐diaminodiphenyl methane (DDM), phenol novolac (PN), 4,4‐diaminodiphenyl sulfone (DDS), and 4,4‐diaminodiphenyl ether (DDE). Thermal properties of cured epoxy resins were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermal gravimetric analysis (TGA). These data were compared with those of the commercial bisphenol A epoxy system. Compared with the bisphenol A epoxy system, the cured 2,6‐dimethyl phenol‐ dicyclopentadiene epoxy resins exhibited lower dielectric constants (～3.0 at 1 MHz and 2.8 at 1 GHz), dissipation factors (～0.007 at 1 MHz and 0.004 at 1 GHz), glass transition temperatures (140–188°C), thermal stability (5% degradation temperature at 382–404°C), thermal expansion coefficients [50–60 ppm/°C before glass‐transition temperature (T_g)], and moisture absorption (0.9–1.1%), but higher modulus (～2 Gpa at 60°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2607–2613, 2003     

Synthesis and characterization of melt‐processable polyimides derived from 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene

A series of molecular‐weight‐controlled imide resins end‐capped with phenylethynyl groups were prepared through the polycondensation of a mixture of 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene and 1,3‐bis(4‐aminophenoxy)benzene with 4,4′‐oxydiphthalic anhydride in the presence of 4‐phenylethynylphthalic anhydride as an end‐capping agent. The effects of the resin chemical structures and molecular weights on their melt processability and thermal properties were systematically investigated. The experimental results demonstrated that the molecular‐weight‐controlled imide resins exhibited not only meltability and melt stability but also low melt viscosity and high fluidability at temperatures lower than 280°C. The molecular‐weight‐controlled imide resins could be thermally cured at 371°C to yield thermoset polyimides by polymer chain extension and crosslinking. The neat thermoset polyimides showed excellent thermal stability, with an initial thermal decomposition temperature of more than 500°C and high glass‐transition temperatures greater than 290°C, and good mechanical properties, with flexural strengths in the range of 140.1–163.6 MPa, flexural moduli of 3.0–3.6 GPa, tensile strengths of 60.7–93.8 MPa, and elongations at break as high as 14.7%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Arylenecyclosiloxane–dimethylsiloxane copolymers

The heterofunctional condensation reaction of 1,4‐bis(phenyldichlorosilyl)benzene with dihydroxydiphenylsilane at a 1:4 ratio of initial compounds in the presence of pyridine was investigated and tetrakis(hydroxydiphenylsiloxy)‐1,4‐bis(phenylsilyl)benzene was obtained. The heterofunctional condensation of the tetrakis(hydroxydiphenylsiloxy)‐1,4‐bis(phenylsilyl)benzene with organotrichlorosilanes at a 1:2 ratio of initial compounds in the presence of pyridine produced dichloro‐containing arylenecyclosiloxanes. The dichloro‐containing arylenecyclosiloxanes were obtained in one stage by successive heterofunctional condensation of 1,4‐bis(dichlorophenylsilyl)benzene with dihydroxydiphenylsilane and organotrichlorosilanes in a 1:4:2 ratio in the presence of pyridine. It was established that the yields of dichloro‐containing products were lower. Hydrolysis of dichloroarylenecyclosiloxanes in a neutral condition produced corresponding dihydroxy compounds. Heterofunctional polycondensation of dicloro(dihydroxy)arylenecyclosiloxanes with α,ω‐dihydroxy(bisdimethylamino)dimethylsiloxanes was used to obtain arylenecyclosiloxane‐dimethylsiloxane copolymers. Thermogravimetric, thermomechanical, and roentgenographic investigations of the synthesized copolymers were carried out. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3142–3148, 2001     

Synthesis and characterization of novel aromatic polyamides via Yamazaki–Higashi phosphorylation method

We synthesized four aromatic diacids: 1,3‐bis(3‐carboxyphenoxy)benzene, 1,4‐bis(4‐carboxyphenoxy)benzene, 1,4‐bis(3‐carboxyphenoxy) benzene, and 1,3‐bis(4‐carboxyphenoxy)benzene, following a procedure of a previously reported synthesis (Ueda and Komatsu, J Polym Sci Part A: Polym Chem 1989, 27, 1017). These diacids were condensed directly with aromatic diamines 4,4′‐oxydianiline (ODA), via the Yamazaki–Higashi phosphorylation method in the presence of triphenylphosphite (TPP), pyridine (Py) and halide salts to give high molecular aromatic polyamides (PAs). The synthesized PAs were obtained in quantitative yields with inherent viscosities between 0.5 and 1.0 dL g^?1. The structures and properties of the obtained PAs were characterized by Fourier transform infrared (FTIR) spectra, nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), polarizing optical microscope (POM). Four PAs all showed good solubility in polar solvents, such as dimethylsulfoxide (DMSO), N,N‐dimethylacetamide (DMAc), N‐dimethylformamide (DMF), 1‐methylpyrrolidone (NMP), and so on. The obtained polymers showed high thermal stability with decomposition temperature around 400°C. The polyamide membranes manifest excellent mechanical properties, with Young's modulus of 2.5–5.5 GPa. Interestingly, the film of PA‐1, PA‐2, and PA‐3 is completely transparent in the visible range, while PA‐4 film is opaque. Crystallization was observed in PA‐4 film, although the molecular structure of PA‐4 is not as symmetrical as PA‐2. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Hydroquinone Based Sulfonated Copolytriazoles with Enhanced Proton Conductivity

A series of new fluorinated sulfonated copolytriazoles (PTHQSH‐XX) with ion exchange capacity (IEC_w) values ranging from 1.66 to 2.82 meq g⁻¹ are prepared via cuprous ion catalyzed azide‐alkyne click polymerization reaction between 1,4‐bis(prop‐2‐ynyloxy)benzene, 4,4′‐diazido‐2,2′‐stilbene disulfonic acid disodium salt (SA), and 4,4‐bis[3′‐trifluoromethyl‐4′(4‐azidobenzoxy) benzyl] biphenyl (QAZ). The degree of sulfonation of the copolytriazoles is adjusted between 60% and 90% by varying the molar ratio of sulfonated monomer (SA) to the nonsulfonated monomer (QAZ). The structure of the copolytriazoles is characterized by Fourier transform infrared and NMR spectroscopy. The solution‐cast membranes of these copolymers exhibit high thermal, mechanical, oxidative and hydrolytic stability, and high proton conductivity (19–142 mS cm⁻¹ at 80 °C and 22–157 mS cm⁻¹ at 90 °C). Transmission electron microscopy confirms the formation of good phase separated morphology with ionic clusters in the range of 15–145 nm.     

Synthesis,crystal structure and electrocatalytic activity of discrete and polymeric copper(II) complexes with bitopic bis(pyrazol-1-yl)methane ligands

New coordination copper(II) compounds containing bitopic bis(pyrazol-1-yl)methane ligands, namely 1,1,2,2-tetrakis(pyrazol-1-yl)ethane, 1,4-bis[bis(pyrazol-1-yl)methyl]benzene and 1,4-bis[bis(3,5-dimethylpyrazol-1-yl)methyl]benzene were prepared. Reactions of ligands with Cu^2 + ions in 1:2 ratio gave discrete homodinuclear complexes, while 1:1 ligand-to-metal ratio lead to the formation of coordination polymers. Electrocatalytic activity of compounds in oxygen electroreduction reaction on the surface of modified carbon paste electrode was evaluated.     

Phosphorus‐containing epoxy resin for an electronic application

A phosphorus‐containing epoxy resin, 6‐H‐dibenz[c,e][1,2] oxaphosphorin‐6‐[2,5‐bis(oxiranylmethoxy)phenyl]‐6‐oxide (DOPO epoxy resin), was synthesized and cured with phenolic novolac (Ph Nov), 4,4′‐diaminodiphenylsulfone (DDS), or dicyandiamide (DICY). The reactivity of these three curing agents toward DOPO epoxy resin was found in the order of DICY > DDS > Ph Nov. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorus‐containing epoxy resin showed lower weight loss temperature and higher char yield than that of bisphenol‐A based epoxy resin. The high char yields and limiting oxygen index (LOI) values as well as excellent UL‐94 vertical burn test results of DOPO epoxy resin indicated the flame‐retardant effectiveness of phosphorus‐containing epoxy resins. The DOPO epoxy resin was investigated as a reactive flame‐retardant additive in an electronic encapsulation application. Owing to the rigid structure of DOPO and the pendant P group, the resulting phosphorus‐containing encapsulant exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the regular encapsulant containing a brominated epoxy resin. High LOI value and UL‐94 V‐0 rating could be achieved with a phosphorus content of as low as 1.03% (comparable to bromine content of 7.24%) in the cured epoxy, and no fume and toxic gas emission were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 353–361, 1999