磷系阻燃环氧树脂研究

本文对近年来国内外9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物（DOPO）衍生物的合成及其应用于阻燃环氧树脂的方法进行介绍，并对所显示的阻燃性、热性能等作了概述和比较。将反应型磷系阻燃剂DOPO衍生物引入环氧树脂基体结构中形成阻燃持久、无卤、低烟、无毒、热稳定性好的新型含磷环氧树脂。     

Synthesis and properties of phosphorus-containing epoxy resins by novel method

Novel phosphorus-containing epoxy resins (1–3% phosphorus content) were synthesized by the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and the diglycidyl ether of bisphenol A and then cured with 4,4′-diaminodiphenyl sulfone or phenol novolac. Differential scanning calorimetry, high performance liquid chromatography, and epoxide equivalent weight titration were used to trace the reaction between the DOPO and the epoxy. The thermal stability and flame retardancy were checked by thermal gravimetric analysis, the limiting oxygen index, and the UL-94 vertical test. The glass transitions were measured by dynamic mechanical analysis. The relation between these properties (thermal stability, flame retardancy, and glass transition) and the DOPO contents (phosphorus content) were discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3903–3909, 1999     

Co-flame retarding effect of ethanolamine modified titanium-containing polyhedral oligomeric silsesquioxanes in epoxy resin

A metal-doped organic and inorganic hybrid polyhedral oligomeric silsesquioxanes (POSS) with a titanium atom in the POSS cage and an ethanolamine substitute group in the corner, namely MEA-Ti-POSS, was synthesized through simple condensation reaction and substitute reaction. It was blended with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to form a kind of blending-type flame retardant system for the modification of epoxy resins. The thermal stability, flame retardancy and mechanical properties of cured epoxy resin composites were studied. Comparing with pure epoxy resin, the LOI value of EP/MEA-Ti-POSS/DOPO composites was raised from 25.2% to 32.7%, and the UL-94 grade reached V-0 level at a loading of the mixture of 5% MEA-Ti-POSS and 5% DOPO. In addition, the cone calorimetry results showed that the heat release rate, total heat release and total smoke production as well as smoke production rate were all reduced during the combustion of EP/MEA-Ti-POSS/DOPO composites. The residual char analysis revealed that carbon residues of EP/MEA-Ti-POSS/DOPO composite served as a physical protective layer to insulate the oxygen and combustible gases to reduce the ablation of the matrix. It was concluded that the mixture of MEA-Ti-POSS and DOPO not only effectively raised the thermal stability and flame retardancy of epoxy composited materials, but also improved their mechanical properties, which expanded a promising application of the metal-POSS derivatives as non-halogen additives in the flame retardant polymers.     

Flame‐retardant epoxy resins from o‐cresol novolac epoxy cured with a phosphorus‐containing aralkyl novolac

A novel phosphorus‐containing aralkyl novolac (Ar‐DOPO‐N) was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) first with terephthaldicarboxaldehyde and subsequently with phenol. The chemical structures of the synthesized compounds were characterized with Fourier transform infrared, ¹H and ³¹P NMR, and elemental analysis. Ar‐DOPO‐N blended with phenol formaldehyde novolac was used as a curing agent for o‐cresol formaldehyde novolac epoxy, resulting in cured epoxy resins with various phosphorus contents. The epoxy resins exhibited high glass‐transition temperatures (159–177 °C), good thermal stability (>320 °C), and retardation on thermal degradation rates. High char yields and high limited oxygen indices (26–32.5) were observed, indicating the resins' good flame retardance. Using a melamine‐modified phenol formaldehyde novolac to replace phenol formaldehyde novolac in the curing composition further enhanced the cured epoxy resins' glass‐transition temperatures (160–186 °C) and limited oxygen index values (28–33.5). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2329–2339, 2002     

Preparation,thermal properties,and flame retardance of epoxy–silica hybrid resins

A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, ¹H and ³¹P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003     

Synthesis and properties of phosphorus-containing bio-based epoxy resin from itaconic acid

A phosphorus-containing bio-based epoxy resin (EADI) was synthesized from itaconic acid (IA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). As a matrix, its cured epoxy network with methyl hexahydrophthalic anhydride (MHHPA) as the curing agent showed comparable glass-transition temperature and mechanical properties to diglycidyl ether in a bisphenol A (DGEBA) system as well as good flame retardancy with UL94 V-0 grade during a vertical burning test. As a reactive flame retardant, its flame-resistant effect on DGEBA/MHHPA system as well as its influence on the curing behavior and the thermal and mechanical properties of the modified epoxy resin were investigated. Results showed that after the introduction of EADI, not only were the flame retardancy determined by vertical burning test, LOI measurement, and thermogravimetric analysis significantly improved, but also the curing reactivity, glass transition temperature (T _g), initial degradation temperature for 5% weight loss (T _d(5%)), and flexural modulus of the cured system improved as well. EADI has great potential to be used as a green flame retardant in epoxy resin systems.     

Thermal and flame retardant properties of epoxy resin cured by a novel phosphorus-containing 4,4′-bisphenol novolac curing agent

A novel flame retardant curing agent for epoxy resin (EP), i.e., a DOPO (9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide)-containing 4,4'-bisphenol novolac (BIP-DOPO) was synthesized and characterized by Fourier transform infrared (FTIR), ¹H NMR, ³¹P NMR spectroscopy, and gel permeation chromatography. The epoxy resin cured by BIP-DOPO itself or its mixture with a commonly used bisphenol A-formaldehyde novolac resin (NPEH720) was prepared. The flame retardancy of the cured EP thermosets were studied by limiting oxygen index (LOI), UL 94 and cone calorimeter test (CCT), and the thermal properties by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the cured epoxy resin EPNP/BI/3/1, which contains 2.2% phosphorus, possesses a value of 26.2% and achieves the UL 94 V-0 rating. The data from cone calorimeter test demonstrated that the peak release rate, average heat release rate, total heat release decline sharply for the flame retarded epoxy resins, compared with those of pure ones. DSC results show that the glass-transition temperatures of cured epoxy resins decrease with increasing phosphorus content. TGA indicates that the incorporation of BIP-DOPO promotes the decomposition of epoxy resin matrix ahead of time and leads to higher char yield. The surface morphological structures of the char residues reveal that the introduction of BIP-DOPO benefits to the formation of a continuous and solid char layer on the epoxy resin material surface during combustion.     

A bio-based epoxy resin derived from p-hydroxycinnamic acid with high mechanical properties and flame retardancy

Recent advances in epoxy resins have been forward to achieving high mechanical performance, thermal stability, and flame retardancy. However, seeking sustainable bio-based epoxy precursors and avoiding introduction of additional flame-retardant agents are still of increasing demand. Here we report the synthesis of p-hydroxycinnamic acid-derived epoxy monomer (HCA-EP) via a simple one-step reaction, and the HCA-EP can be cured with 4,4′-diaminodiphenylmethane (DDM) to prepare epoxy resins. Compared with the typical petroleum-based epoxy resin, bisphenol A epoxy resin, the HCA-EP-DDM shows a relatively high glass transition temperature (192.9 °C) and impressive mechanical properties (tensile strength of 98.3 MPa and flexural strength of 158.9 MPa). Furthermore, the HCA-EP-DDM passes the V-1 flammability rating in UL-94 test and presents the limiting oxygen index of 32.6%. Notably, its char yield is as high as 31.6% under N₂, and the peak heat rate release is 60% lower than that of bisphenol A epoxy resin. Such findings provide a simple way of using p-hydroxycinnamic acid instead of bisphenol A to construct high-performance bio-based thermosets.     

Synergistic effect of flame retardants and graphitic carbon nitride on flame retardancy of polylactide composites

In order to improve the flame retardant of polylactide (PLA), the synergistic effect of graphitic carbon nitride (g‐C₃N₄) with commercial‐available flame retardants melamine pyrophosphate (MPP) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was investigated. The PLA composites containing 5 wt% g‐C₃N₄ and 10 wt% DOPO had a highest limited oxygen index (LOI) value of 29.5% and reached the V‐0 rating of UL‐94 test. The cone calorimeter tests exhibited that DOPO had a better synergistic effect with g‐C₃N₄ than MPP to improve flame retardancy of PLA. The peak heat release rate (pHRR) and total heat release (THR) of PLA composites containing 10 wt% DOPO could be reduced by 25.2% and 23.6%, respectively, as compared with those of pure PLA. The presence of rich phosphorus element and aromatic groups in DOPO contributed to obtain continuous compact char layer and increase the graphitization level of char residues, thereby, resulting in improving the flame retardancy of PLA together with g‐C₃N₄. In addition, the incorporation of DOPO can serve as a plasticizer to reduce the complex viscosity, improving the processability of PLA composites.     

Preparation and properties of high performance epoxy–silsesquioxane hybrid resins prepared using a maleimide–alkoxysilane compound as a modifier

An alkoxysilane compound possessing maleimide moiety (MSM) was prepared from N‐(4‐hydroxyphenyl)maleimide and 3‐glycidoxypropyltrimethoxysilane and was used as a modifier of epoxy resins. In situ curing epoxy resins with MSM resulted in epoxy resins with good homogeneity. Just 5–10 wt % of MSM is sufficient to yield high glass transition temperature (165 °C), good thermal stability above 360 °C, and high flame retardancy (LOI = 30) to bisphenol‐A‐based epoxy resins. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5787–5798, 2005     

Synthesis,Characterization and Polymerization of a Novel Glycidyl Phosphinate

With the aim to obtain flame‐retardant epoxy resins, a new glycidyl phosphinate, 9‐(9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide)‐2,3‐epoxypropyl (DOPO‐Gly) was synthesized via a two‐step synthesis. The subsequent reaction of DOPO‐Gly with BF₃·Et₂O resulted in a polyether with a pendant bulky phosphorylated group. Likewise, the reaction with phthalic acid anhydride gave the expected dihydroxy ester. However, the reaction with tertiary or primary amines led to isomerization and no polymer was obtained.     

Synergistic effect of DOPO immobilized silica nanoparticles in the intumescent flame retarded polypropylene composites

The synergistic effect of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) immobilized silica (SiO₂‐DOPO) nanoparticles with an intumescent flame retardant (IFR) on the flame retardancy of polypropylene (PP) was investigated by UL 94 vertical tests and limiting oxygen index (LOI) measurements. It was found that the PP/IFR composites (25 wt%) achieved the UL94 V0 grade and LOI increased to 32.1 with an incorporation of 1.0 wt% SiO₂‐DOPO nanoparticles. Based on thermogravimetric analysis, scanning electronic microscopy and rheological analysis, it is speculated that three factors are mainly contributed to the improvement of the flame retardancy. First, the thermal stability of PP/IFR composites was improved by incorporating SiO₂‐DOPO nanoparticles. Second, the presence of SiO₂‐DOPO nanoparticles could induce the formation of a continuous char skin layer during combustion. The compact char layer could effectively impede the transport of bubbles and heat. Third, rheological analysis indicated that SiO₂‐DOPO nanoparticles could increase viscosity of the PP/IFR composites, which was also benefited to increase flame retardancy. Copyright © 2013 John Wiley & Sons, Ltd.     

Vanillin‐derived phosphorus‐containing compounds and ammonium polyphosphate as green fire‐resistant systems for epoxy resins with balanced properties

Flame retardants from vanillin when utilized together with ammonium polyphosphate (APP) yield excellent synergistic flame retardancy toward epoxy resins. Bisphenol A epoxy resins have been widely used due to their excellent mechanical properties, chemical resistance, electrical properties, adhesion, etc., while they are flammable. Environment‐friendly and bio‐based flame retardants have captured increasing attention due to their ecological necessity. In this paper, 3 bio‐based flame retardants were synthesized from abundant and more importantly renewable vanillin, and their chemical structures were determined by ¹H NMR and ¹³C NMR. They were used together with APP (an environment‐friendly commercial flame retardant) to improve the fire resistance of bisphenol A epoxy resin. With the addition APP content of 15 phr, the modified bisphenol A epoxy resin could reach UL‐94V0 rating during vertical burning test and limit oxygen index values of above 35%, but reducing APP content to 10 phr, the flame retardancy became very poor. With the total addition content of 10 phr, the epoxy resins modified by 7 to 9 phr APP and 1 to 3 phr bio‐based flame retardants with epoxy groups or more benzene rings showed excellent flame retardancy with UL‐94V0 rating and limit oxygen index values of around 29%. The T_gs of the epoxy resins could be remained or even increased after introducing bio‐based flame retardants, as the control; those of APP alone‐modified epoxy resins compromised a lot. The green synergistic flame‐retardant systems have a great potential to be used in high‐performance materials.     

Synthesis, characterization, and cure properties of phosphorus-containing epoxy resins for flame retardance

An organophosphorus compound, 10-(2,5-dihydroxyl phenyl)-9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DHPDOPO), was synthesized through the reaction of 9,10-dihydro-9-oxa-10-phosphaphnanthrene-10-oxide (DOPO) and p-benzoquinone, and characterized by elemental analysis, Fourier transform infrared spectrum (FTIR), and ¹H-NMR and ³¹P-NMR spectroscopes. Consequently, the phosphorus-containing epoxy resins with phosphorus content of 1 and 2 wt.% were prepared via the reaction of diglycidyl ether of bisphenol-A with DHPDOPO and bisphenol-A, and confirmed with FTIR and gel permeation chromatography (GPC). Phenolic melamine, novolak, and dicyanodiamide (DICY) were used as curing agents to prepare the thermosetted resins with the control and the phosphorus-containing epoxy resins. Thermal properties and thermal degradation behaviors of these the thermosetted resins were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Phenolic melamine-cured resins exhibited higher glass transition temperatures than the other cured resins due to the high rigidity of their molecular chain. TGA studies demonstrated that the decomposition temperatures of the novolak-cured resins were higher than those of the others. A synergistic effect from the combination of the phosphorus-containing epoxy resin and the nitrogen-containing curing agent can result in a great improvement of the flame retardance for their thermosetted resins.     

Novel flame retardancy effects of DOPO-POSS on epoxy resins

A series of flame retarded epoxy resins (EP) was prepared with a novel polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS). The flame retardancy of these EPs was tested by the LOI, UL-94, which indicates that DOPO-POSS has meaningful effects on the flame retardancy of EP composites. 2.5 wt.% DOPO-POSS incorporation into epoxy resin (EP-2.5), results in a LOI value 30.2 and UL-94 V-1 (t₁ = 8 s and t₂ = 3 s) rating. Moreover, self-extinguishing effect through the pyrolytic gases spurt is observed in UL-94 test for the EP-2.5. The pyrolytic gases and thermal stability of epoxy resins with and without DOPO-POSS were detected by TGA-FTIR under air atmosphere. Releases of gaseous species are found to be similar for the pure EP and EP-2.5. The details of fire behaviour, such as TTI, HRR, p-HRR, TSR, SEA, COPR, CO₂PR, and TML, were tested by cone calorimeter. It is notable that 2.5 wt.% DOPO-POSS could make COPR and CO₂PR reach a maximum, which could explain the blowing-out extinguishing effect.     

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%.     

Low flammability and smoke epoxy resins with a novel DOPO‐based imidazolone derivative

In this work, a DOPO‐based imidazolone derivative named DHI was synthesized using DOPO, 5‐amino‐2‐benzimidazolinone and 4‐hydroxybenzaldehyde as raw materials. The chemical structure of DHI was characterized by ¹H‐NMR, ³¹P‐NMR and Fourier transform infrared spectra (FTIR). Then, a series of different flame‐retardant epoxy resin (EP) thermosets were prepared by mixing flame retardant DHI. The thermal properties of the cured EPs was investigated by thermogravimetry analysis (TGA) and differential scanning calorimeter (DSC), and the results showed the thermal stability and glass transition temperature (T_g) of the cured EP modified with DHI declined slightly compared with that of neat EP. The limited oxygen index (LOI) and UL94 test results exhibited DHI imparted good flame retardancy to EP. The EP‐4 (phosphorus content of 1.25%) possessed a LOI value of 36.5% and achieved a V‐0 rating. Furthermore, the peak of heat release rate (PHRR) and total heat release rate (THR) of EP‐4 decreased by 38.7% and 24.5%, respectively. Excitedly, the total smoke production (TSP) of EP‐4 sample declined by 62.5%, which meant DHI also made EP obtain excellent smoke suppression property. Moreover, the flame‐retardant mechanism was studied by scanning electron microscopy (SEM) and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). It was reasonable inferred that DHI could not only promote EP to form dense char layer in condensed phase, but also restrain combustion in gaseous phase through catching the free radicals sourced from the degradation of EP.     

Synergetic effect of thermal conductivity and flame retardancy of cyanate ester composites containing DOPO and BN with great dielectric properties

DOPO and boron nitride (BN) fillers with different particle sizes and several loadings were employed to improve the properties of cyanate ester (CE) resin. The effects of BN content and particle size on the thermal conductivity of the BN‐DOPO/CE ternary composites were discussed. The influence of enhancing the thermal conductivity of the ternary composites on their flame retardancy was studied. The consequences showed that increasing the thermal conductivity of BN‐DOPO/CE composites had an active impact on their flame retardancy. Approving flame retardancy of the ternary composites was certified by the high limiting oxygen index (LOI), UL‐94 rating of V‐0, and low heat release rate (HRR) and total heat release (THR). For instance, in contrast with pure CE matrix, peak of HRR (pk‐HRR), average of HRR (av‐HRR), THR, and average of effective heat of combustion (av‐EHC) of CEP/BN_{0.5 μm}/10 composite were decreased by 51.7%, 33.8%, 18.7%, and 18.9%, respectively. Thermal gravimetry analysis (TGA) showed that the addition of BN fillers improves the thermal stability of the composites. Moreover, the ternary composites possess good dielectric properties. Their dielectric constants (ε) are less than 3, and dielectric loss tangent (tgδ) values are lower than neat CE resin.     

Enhanced thermal properties and flame retardancy of unsaturated polyester‐based hybrid materials containing phosphorus and silicon

A phosphorus and silicon containing liquid monomer (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide–vinyltrimethoxysilane (DOPO–VTS)) was synthesized by the reaction between DOPO and VTS. DOPO–VTS and methacryloxypropyltrimethoxylsilane were introduced into unsaturated polyester resin to prepare flame retardant UPR/SiO₂ (FR‐UPR/SiO₂) hybrid materials by sol–gel method and curing process. DOPO–VTS contributes excellent flame retardancy to UPR matrix, which was confirmed by the limiting oxygen index and microscale combustion calorimeter results. The thermogravimetric analysis (TGA) results indicate that the FR‐UPR/SiO₂ hybrid materials possess higher thermal stability and residual char yields than those of pure UPR at high temperature region. The thermal degradation of materials was investigated by TGA/infrared spectrometry (TG‐IR) and real‐time infrared spectrometry (RT‐IR), providing insight into the thermal degradation mechanism. Moreover, scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) were used to explore the morphologies and chemical components of the residual char. Copyright © 2013 John Wiley & Sons, Ltd.     

The non-halogen flame retardant epoxy resin based on a novel compound with phosphaphenanthrene and cyclotriphosphazene double functional groups

A novel flame retardant additive hexa-(phosphaphenanthrene -hydroxyl-methyl-phenoxyl)-cyclotriphosphazene (HAP-DOPO) with phosphazene and phosphaphenanthrene double functional groups has been synthesized from hexa-chloro-cyclotriphosphazene, 4-hydroxy-benzaldehyde and 9,10-dihydro-9-oxa-10- phosphaphenanthrene 10-oxide(DOPO). The structure of HAP-DOPO was characterized by Fourier transformed infrared (FT-IR) spectroscopy and ¹H nuclear magnetic resonance (¹H NMR) and ³¹P nuclear magnetic resonance (³¹P NMR). The additive HAP-DOPO was blended into diglycidyl ether of bisphenol-A (DGEBA) to prepare flame retardant epoxy resins. The flame retardant properties and thermal properties of the epoxy resins cured by 4, 4′-Diamino-diphenyl sulfone (DDS) were investigated from the differential scanning calorimeter (DSC), the thermogravimetric analysis (TGA), UL94 test, the limiting oxygen index (LOI) test and Cone calorimeter. Compared to traditional DOPO-DGEBA and ODOPB-DGEBA thermosets, the HAP-DOPO/DGEBA thermosets have higher T_gs at the same UL94 V-0 flammability rating for their higher crosslinking density and have higher char yield and lower pk-HRR at same 1.2 wt.% phosphorus content which confirm that HAP-DOPO has higher flame retardant efficiency on thermosets. The scanning electron microscopy (SEM) results shows that HAP-DOPO in DGEBA/DDS system obviously accelerate formation of the sealing, stronger and phosphorus-rich char layer to improve flame retardant properties of matrix during combustion.