Synthesis and characterization of polyfunctional crosslinking agents for cyanate resins

An efficient crosslinking monomer for a mixed cyanate/epoxy resin system, bisphenol-A-monocyanate monoglycidyl ether 3 , has been synthesized and characterized. The intermediate compound, the monoglycidyl ether of bisphenol-A 2 , was also isolated and purified by extraction and chromatographic separation using a silica gel column. The cyanate functional group in the crosslinking monomer 3 can be cured easily by heat to form a triazine structure 8 , but the epoxy functional group in the crosslinking monomer 3 can not be cured without affecting the cyanate group because the latter is more reactive both under heat and basic conditions. A practical approach for the application of the crosslinking monomer 3 is discussed and tested. Most interestingly, under heat curing, a very tough and strong resin material was produced from this crosslinking mixed resin mixture. By using a secondary amine, diethylamine, as a curing agent, the cyanate groups in the crosslinking monomer 3 react to form the structures 11 or 12 , depending on the molar ratio of monomer 3 to diethylamine. A bifunctional crosslinking agent for a mixed cyanate (thermoset) and polyolefin (thermoplastic) resin system, 2-allylphenyl cyanate 16 , has also been synthesized and characterized. Like 3 , 2-allylphenyl cyanate 16 easily forms the crosslinking triazine compound 17 upon heating. 17 is a crystalline solid with mp = 110–111°C. As a crosslinking agent, 2-allylphenyl cyanate 16 reacts not only with itself, but also with other cyanates to form heterogeneous triazine rings, exemplified by triazines 18 and 19 . Even though it does not self polymerize through the allyl double bond, it can copolymerize with an other olefinic monomer, such as methyl methacrylate, to form a crosslinked and insoluble polymer. © 1995 John Wiley & Sons, Inc.     

酚醛型氰酸酯与双酚A型环氧共固化反应的FTIR研究

在恒温固化条件下,通过FTIR跟踪方法,研究了酚醛型氰酸酯与双酚A型环氧共固化反应的路径及其反应机理.共固化体系的反应过程包括在150℃及其以下温度,主要发生的是氰酸酯的三嗪环化固化反应,其中三嗪环化固化反应由于环氧的加入,反应速率被极大地提高了;同时,酚醛型氰酸酯中的氨基甲酸酯类杂质与环氧发生开环聚合反应,引起环氧官能团产生弱而持续的消耗.但在此阶段,酚醛型氰酸酯与环氧之间没有化学反应发生;在180℃及其以上温度,三嗪环和环氧发生反应,异构为异氰脲酸环结构,并进一步反应生成唑啉酮环结构,由于该反应的发生,促进了环氧官能团的消耗速度,在环氧官能团的转化率-时间图中,出现倒S曲线;在三嗪环的转化率图中,出现一个极大值后再降落的曲线.反应温度的提高有利于促进酚醛型氰酸酯与环氧之间的共固化反应,特别是当反应温度为220℃时,氰酸酯官能团和环氧官能团的消耗、三嗪环和唑啉酮环的生成均以较快的速率进行,—OCN生成三嗪环的转化率可以较容易地达到1,而唑啉酮环的转化率不超过0.5.     

DSC-TG studies on kinetics of curing and thermal decomposition of epoxy–ether amine systems

The cure behavior of diglycidyl ether of bisphenol A with a simple ether amine (4,7,10, trioxa -1,13, tridecane diamine), system I and a polyether amine (polypropylene glycol block polyethylene glycol block polypropylene glycol bis 2 amino propyl ether), system II was compared by Differential Scanning Calorimetry. The exothermicity of the curing reaction of system I is higher than that of system II (316 ± 15 J g^?1 for System I and 230 ± 15 J g^?1 for system II). Kinetic parameters viz., activation energy, pre-exponential factor, and rate constant for curing were evaluated by Kissinger method and Kissinger–Akahira–Sunose isoconversion method. Both systems showed low glass transition temperatures and System II shows a much lower T _g (?38 °C) than system I (26 °C). The thermogravimetric analysis of the two cured epoxy amine systems showed comparable thermal stability.     

Phase structure and thermomechanical properties of primary and tertiary amine‐cured epoxy/silica hybrids

Several kinds of organic–inorganic hybrids were synthesized from an epoxy resin and a silane alkoxide with a primary amine‐type curing agent or tertiary amine curing catalyst. In the hybrid systems cured with the primary amine‐type curing agent, the storage modulus in the high‐temperature region increased, and the peak area of the tan δ curve decreased. Moreover, the mechanical properties were improved by the hybridization of small amounts of the silica network. However, these phenomena were not observed in the hybrid systems cured with the tertiary amine catalyst. The differences in the network structures of the hybrid materials with the different curing processes were characterized with Fourier transform infrared (FTIR). In the hybrid systems cured with the primary amine‐type curing agent, FTIR results showed the formation of a covalent bond between silanol and hydroxyl groups that were generated by the reaction of an epoxy group with an active hydrogen of the primary amine. However, this phenomenon was not observed in the hybrids cured with the tertiary amine. The hybrids with the primary amine showed a homogeneous microstructure in transmission electron microscopy observations, although the hybrids cured with the tertiary amine showed a heterogeneous structure. These results mean that the differences in the interactions between the organic and inorganic phases significantly affect the properties and microstructures of the resultant composites. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1071–1084, 2001     

NCOCH2(CF2)6CH2OCN cyanate ester resin. A detailed study

The NCOCH₂(CF₂)₆CH₂OCN fluoromethylene cyanate ester monomer and resin are synthesized and characterized. The monomer is prepared by a large‐scale bench‐top synthesis, characterized by differential scanning calorimetry, infrared, ¹H‐, ¹³C‐, ¹⁵N‐, and ¹⁹F‐NMR spectroscopies and analyzed for catalytically active impurities. Conversion of the monomer to prepolymer and cured resin is characterized by IR and NMR spectroscopies and kinetically analyzed. Resin properties characterization includes thermal, tensile, dynamic mechanical, dielectric, refractive index, thermodielectric and thermogravimetric stabilities, and water absorption. Relevant property comparisons with the commercial AroCy F cyanate ester resin (6F bisphenol A dycyanate) and a Jeffamine‐bisphenol diglycidyl ether epoxy are made. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 135–150, 1999     

Studies on thermal and morphological properties of 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane-epoxy-bismaleimide matrices

A new cyanate ester monomer, 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane has been synthesized and characterized. Epoxy modified with 4, 8 and 12% (by weight) of cyanate ester were made using epoxy resin and 1,1-bis(3-methyl-4-cyanatophenyl)cyclohexane and cured by using diaminodiphenylmethane. The cyanate ester modified epoxy matrix systems were further modified with 4, 8 and 12% (by weight) of bismaleimide (N,N′-bismaleimido-4,4′-diphenylmethane). The formation of oxazolidinone and isocyanurate during cure reaction of epoxy and cyanate ester blend was confirmed by IR spectral studies. Bismaleimide-cyanate ester-epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. Thermal studies indicate that the introduction of cyanate ester into epoxy resin improves the thermal degradation studies at the expense of glass transition temperature. Whereas the incorporation of bismaleimide into epoxy resin enhances the thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influences the thermal properties according to their percentage content. DSC thermogram of cyanate ester modified epoxy and bismaleimide modified epoxy show unimodel reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured bismaleimide modified epoxy and cyanate ester-epoxy systems increased with increasing bismaleimide content. The morphology of the bismaleimide modified epoxy and cyanate ester-epoxy systems were also studied by scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.     

Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker

A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103     

High resolution solid‐state 13C‐NMR study of as‐cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the physico‐chemical modifications of aliphatic or aromatic amine‐cured epoxy resins based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins have a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid‐state ¹³C‐NMR spectroscopy we show that the aliphatic amine‐cured resin (DGEBA‐TETA) appears much more sensitive to gamma rays than the aromatic amine‐cured one (DGEBA‐DDM). On the one hand, qualitative analyses of the high resolution solid‐state ¹³C‐NMR spectra of both epoxy resins, irradiated under similar conditions (8.5 MGy), reveal almost no change in the aromatic amine‐cured resin whereas new resonances are observed for the aliphatic amine‐cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acids and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are investigated by measuring the relaxation times, T_CH, T_1ρH and T_1C , before and after irradiation. The study of relaxation data shows the formation, under irradiation, of a more rigid network, especially for the aliphatic amine‐cured system and confirms that aromatic amine‐cured resin [DGEBA‐4,4′‐diaminodiphenylmethane(DDM)] is much less affected by ionizing radiations than the aliphatic amine‐cured resin [DGEBA‐triethylenetetramine(TETA)]. Moreover, it has been shown that the molecular modifications generated by irradiation on the powder of the aliphatic‐amine‐cured resin appear to be homogeneously distributed inside the polymers as no phase separations can be deduced from the above analyses. Copyright © 2001 John Wiley & Sons, Ltd.     

Cure Kinetics of Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine System

The cure kinetics of epoxy based on the diglycidyl ether of bisphenol A (DGEBA) modified with different amounts of poly(acrylonitrile-butadiene-styrene) (ABS) and cured with 4,4′-diaminodiphenylsulfone (DDS) was investigated by employing differential scanning calorimetry (DSC). The curing reaction was followed by using an isothermal approach over the temperature range 150–180°C. The amount of ABS in the blends was 3.6, 6.9, 10 and 12.9 wt%. Blending of ABS in the epoxy monomer did not change the reaction mechanism of the epoxy network formation, but the reaction rate seems to be decreased with the addition of the thermoplastic. A phenomenological kinetic model was used for kinetic analysis. Activation energies and kinetic parameters were determined by fitting the kinetic model with experimental data. Diffusion control was incorporated to describe the cure in the latter stages, predicting the cure kinetics over the whole range of conversion. The reaction rates for the epoxy blends were found to be lower than that of the neat epoxy. The reaction rates decreased when the ABS contents was increased, due to the dilution effect caused by the ABS on the epoxy/amine reaction mixture.     

Network structure and thermomechanical properties of hybrid DGEBA networks cured with 1‐methylimidazole and hyperbranched poly(ethyleneimine)s

The use of commercially available hyperbranched poly(ethyleneimine)s (Lupasol?, BASF) as polymeric modifiers in diglycidyl ether of bisphenol A thermosetting formulations using 1‐methylimidazole (MI) as anionic initiator has been studied. Poly(ethyleneimine)s can get incorporated into the network structure by condensation of amine and epoxy groups. The excess, over‐stoichiometric epoxy groups can undergo anionic homopolymerization initiated by MI. The thermal, dynamomechanical, and mechanical properties of the resulting materials have been determined using DSC, thermomechanical analysis (TMA), dynamomechanical analysis (DMA), and mechanical testing. The effect of the different amine modifiers on the MI networks, determined by their structure, is complex. Low initiator content and high molecular weight modifiers create significant mobility restrictions, which have a strong effect on the glass transition temperature and the apparent crosslinking density of the cured materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Evolution of structure and properties of a liquid crystalline epoxy during curing

The evolution of structure, and thermal and dynamic mechanical properties of a liquid crystalline epoxy during curing has been studied with differential scanning calorimetry (DSC), polarized optical microscopy, x-ray scattering, and dynamic mechanical analysis. The liquid crystalline epoxy was the diglycidyl ether of 4,4′-dihydroxy-α-methylstilbene (DGEDHMS). Two curing agents were used in this study: a di-functional amine, the aniline adduct of DGEDHMS, and a tetra-functional sulfonamido amine, sulfanilamide. The effects of curing agent, cure time, and cure temperature have been investigated. Isothermal curing of the liquid crystalline epoxy with the di-functional amine and the tetra-functional sulfonamido amine causes an increase in the mesophase stability of the liquid crystalline epoxy resin. The curing also leads to various liquid crystalline textures, depending on the curing agent and cure temperature. These textures coarsen during the isothermal curing. Moreover, curing with both curing agents results in a layered structure with mesogenic units aligned perpendicular to the layer surfaces. The layer thickness decreases with cure temperature for the systems cured with the tetra-functional curing agent. The glass transition temperature of the cured networks rises with increasing cure temperature due to the increased crosslink density. The shear modulus of the cured networks shows a strong temperature dependence. However, it does not change appreciably with cure temperature. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2363–2378, 1997     

环氧树脂与氰酸酯共固化反应的研究

应用DSC、FT IR对乙酰丙酮过渡金属络合物催化促进的环氧树酯与氰酸酯共固化反应行为、历程以及固化物的结构特征进行了研究探讨 .结果表明 ,促进剂能够明显的降低固化反应温度 ,缩短固化反应时间 .反应历程首先是氰酸酯发生自聚反应形成二聚体或三聚体 (三嗪环 ) ,然后二聚体可进一步共聚形成三嗪环 ,此过程伴随着环氧基的聚醚反应 ,最后是三嗪环与剩余的环氧基反应形成唑烷酮 .在氰酸酯欠量的条件下 ,固化树脂中主要是唑烷酮和聚醚结构 ,三嗪环结构很少 ;在氰酸脂适量或过量条件下 ,固化树脂主要是三嗪环和唑烷酮结构 ,聚醚结构很少 .     

Synthesis and properties of biobased epoxy resins. part 1. Glycidylation of flavonoids by epichlorohydrin

Biobased epoxy resins were synthesized from a catechin molecule, one of the repetitive units in natural flavonoid biopolymers also named condensed tannins. The reactivity of catechin toward epichlorohydrin to form glycidyl ether derivatives was studied using two model compounds, resorcinol and 4‐methylcatechol, which represent the A and B rings of catechin, respectively. These model molecules clearly showed differences in reactivity upon glycidylation, explaining the results found with catechin monomer. The reaction products were characterized by both FTIR and NMR spectroscopy and chemical assay. The glycidyl ether of catechin (GEC) was successfully cured in various epoxy resin formulations. The GECs thermal properties showed that these new synthesized epoxy resins displayed interesting properties compared to the commercial diglycidyl ether of bisphenol A (DGEBA). For instance, when incorporated up to 50% into the DGEBA resin, GEC did not modify the glass‐transition temperature. Epoxy resins formulated with GEC had slightly lower storage moduli but induced a decrease of the swelling percentage, suggesting that GEC‐enhanced crosslinking in the epoxy resin networks. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Epoxy resins from novel monomers with a bis‐(9,10‐dihydro‐9‐oxa‐10‐oxide‐10‐phosphaphenanthrene‐10‐yl‐) substituent

A new diepoxide and a new diamine, both bearing bis‐(9,10‐dihydro‐9‐oxa‐10‐oxide‐10‐phosphaphenanthrene‐10‐yl‐)‐substituted methylene linkages, were prepared through the reaction of 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide with benzophenone derivatives via a simple addition reaction followed by a dehydration reaction. These two compounds were used as monomers for preparing cured epoxy resins with high phosphorus contents. The resultant epoxy resins showed high glass‐transition temperatures (between 131 and 196 °C). All of the cured epoxy resins exhibited high thermal stability, with 5% weight loss temperatures over 316 °C, and excellent flame retardancy, with limited oxygen index values of 37–50. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 359–368, 2002     

Synthesis of 4,4′‐bis (4‐oxyphenoxy)benzophenone diglycidyl ether and the thermal stability for blends with 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexanecarboxylate

We synthesized novel aromatic epoxy, 4,4′‐bis(4‐oxyphenoxy)benzophenone diglycidyl ether (DGEEK), by a three step reaction sequence and then it was blended with 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexanecarboxylate (CAE). The DGEEK structure was confirmed by FT‐IR and ¹H‐NMR measurement. Also, we investigated thermal properties of DGEEK/CAE blend epoxy by differential scanning calorimeter (DSC) and thermogravimetry analyzer (TGA). The glass transition temperature increased but initial decomposition temperature of cured epoxy decreased through the increasing amounts of ether–ether–ketone group of the epoxy network structure. By increasing the DGEEK mole fraction in the DGEEK/CAE blend epoxy matrix, the curing peak temperature decreased and the curing activation energy for DGEEK/CAE blend epoxy systems showed a considerable decrease. Copyright © 2001 John Wiley & Sons, Ltd.     

Nonaqueous synthesis of nanosilica in epoxy resin matrix and thermal properties of their cured nanocomposites

Nonaqueous synthesis of nanosilica in diglycidyl ether of bisphenol‐A epoxy (DGEBA) resin has been successfully achieved in this study by reacting tetraethoxysilane (TEOS) directly with DGEBA epoxy matrix, at 80 °C for 4 h under the catalysis of boron trifluoride monoethylamine (BF₃MEA). BF₃MEA was proved to be an effective catalyst for the formation of nanosilica in DGEBA epoxy under thermal heating process. FTIR and ²⁹Si NMR spectra have been used to characterize the structures of nanosilica obtained from this direct thermal synthetic process. The morphology of the nanosilica synthesized in epoxy matrix has also been analyzed by TEM and SEM studies. The effects of both the concentration of BF₃MEA catalyst and amount of TEOS on the diameters of nanosilica in the DGEBA epoxy resin have been discussed in this study. From the DSC analysis, it was found that the nanosilica containing epoxy exhibited the same curing profile as pure epoxy resin, during the curing reaction with 4,4′‐diaminodiphenysulfone (DDS). The thermal‐cured epoxy–nanosilica composites from 40% of TEOS exhibited high glass transition temperature of 221 °C, which was almost 50 °C higher than that of pure DGEBA–DDS–BF₃MEA‐cured resin network. Almost 60 °C increase in thermal degradation temperature has been observed during the TGA of the DDS‐cured epoxy–nanosilica composites containing 40% of TEOS. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 757–768, 2006     

环氧树脂与氰酸酯共聚反应研究

研究了催化剂对环氧树脂与氰酸酯树脂的共聚固化反应行为的影响,并初步探索氰酸酯／环氧固化的反应历程．研究表明,催化剂能明显地促进其固化反应,降低固化温度,缩短固化时间;氰酸酯与环氧共聚反应历程是首先氰酸酯三聚反应生成三嗪环结构,然后三嗪环开环与环氧共聚反应,最后是未能参与共聚反应的环氧官能团在唑啉结构和三嗪环的催化下发生聚醚化反应;在氰酸酯官能团欠量的条件下,固化树脂中主要是唑啉和聚醚结构,而三嗪环结构的含量很少．     

NMR investigations of the possible cross reactions between cyanate and epoxy resins

The possible cross reactions indicated by solid-state NMR between cyanate functionalized resin and epoxy functionalized resin have been investigated by using both natural abundance and labeled monofunctional model compounds. These soluble products were isolated and purified by silica gel adsorption chromatography and gel permeation chromatography. They were fully characterized by high resolution ¹H-, ¹³C-, ¹⁵N-NMR spectroscopy and by mass spectrometry. The major cross-reaction product is a racemic mixture of enantiomers, which contain an oxazolidinone ring formed by one cyanate molecule and two epoxy molecules. However, epoxy consumption lags cyanate consumption in the overall reaction as triazine formation from the cyanate is much faster than the two competing reactions, the cross reaction between cyanate and epoxy, and the self-polymerization of epoxy, under the conditions investigated. The cross reaction between cyanate and epoxy is limited. Approximately 12% of cross reaction between cyanate and epoxy was found in the overall reaction. In addition to the cross reactions of epoxy and cyanate, the reactions of epoxy and the carbamate, which is the major side product for the curing reaction of cyanate resin in solution, have also been investigated, and the mechanism of these reactions discussed. From the reactions of epoxy and carbamate, several products related to cross reaction between epoxy and cyanate have been isolated and identified. It is suggested that the reaction of epoxy and carbamate is one of the pathways in the overall cross reaction between epoxy and cranate resins. Finally, the mechanism of the overall cross-curing reaction between the diepoxy and dicyanate mixed resins is discussed. © 1994 John Wiley & Sons, Inc.     

Synthesis,Characterization, Curing and Shape Memory Properties of Epoxy‐Polyether System

Epoxy resins were cured by an amine telechelic poly(tetramethylene oxide) (PTMO). The telechelic amine was synthesized from hydroxy telechelic PTMO and was characterized. The kinetics of curing of epoxy monomer by the polyether amine was studied in detail by differential scanning calorimetry (DSC) and rheology to optimize the cure conditions. The cured epoxy system exhibited shape memory properties where PTMO served as the switching segment. Molar ratios of the epoxy monomer and the amine were varied to get polymers with different compositions. The developed polymers were analyzed by DSC, X‐ray diffraction, and Dynamic Mechanical Thermal (DMTA) analyses. Shape memory property was evaluated by bending tests. As the concentration of epoxy resin increased, the transition temperature (T_trans) increased. The tensile strength and % elongation also increased with epoxy resin‐content. The extent of shape recovery increased with PTMO‐content with a minor penalty in recovery time. The polymer with the maximum PTMO‐content exhibited 99% shape recovery with a recovering time of 12 s.     

Thermal and physical properties of flame-retardant epoxy resins containing 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4-naphthalenediol and cured with dicyanate ester

2-(6-oxido-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)-1,4-naphthalenediol (DOPONQ) was prepared by the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with 1,4-naphthoquinone. The phosphorus-containing diol (DOPONQ) was used as a reactive flame retardant by an advancement reaction with the diglycidyl ether of bisphenol-A epoxy (DGEBA) resin at various stoichiometric ratios. DOPONQ-containing advanced epoxy was separately cured with various dicyanate esters to form flame-retardant epoxy/cyanate ester systems. The effect of the phosphorus content and dicyanate ester structure on the curing characteristic, glass transition temperature, dimensional stability, thermal stability, flame retardancy, and dielectric property was studied and compared with that of the control advanced bisphenol-A epoxy system. The DOPONQ-containing epoxy/cyanate ester systems exhibited higher glass transition temperatures as well as better thermal dimensional and thermal degradation stabilities. The flame retardancy of the phosphorus-containing epoxy/dicyanate ester system increased with the phosphorus content, and a UL-94 V-0 rating could be achieved with a phosphorus content as low as 2.1%.