Synthesis of a novel phosphorus‐containing dicyclopentadiene novolac hardener and its cured epoxy resin with improved thermal stability and flame retardancy

A novel phosphorus‐containing dicyclopentadiene novolac (DCPD‐DOPO) curing agent for epoxy resins, was prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and n‐butylated dicyclopentadiene phenolic resin (DCPD‐E). The chemical structure of the obtained DCPD‐DOPO was characterized with FTIR, ¹H NMR and ³¹P NMR, and its molecular weight was determined by gel permeation chromatography. The flame retardancy and thermal properties of diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with DCPD‐DOPO or the mixture of DCPD‐DOPO and bisphenol A‐formaldehyde Novolac resin 720 (NPEH720) were studied by limiting oxygen index (LOI), UL 94 vertical test and cone calorimeter (CCT), and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. It is found that the DCPD‐DOPO cured epoxy resin possess a LOI value of 31.6% and achieves the UL 94 V‐0 rating, while its glass transition temperature (T_g) is a bit lower (133 °C). The T_g of epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 increases to 137 °C or above, and the UL 94 V‐0 rating can still be maintained although the LOI decreases slightly. The CCT test results demonstrated that the peak heat release rate and total heat release of the epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 decrease significantly compared with the values of the epoxy resin cured by NPEH720. Moreover, the curing reaction kinetics of the epoxy resin cured by DCPD‐DOPO, NPEH720 or their mixture was studied by DSC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44599.     

Novel flame retardant thermosets from nitrogen‐containing and phosphorus‐containing epoxy resins cured with dicyandiamide

A novel phosphorus‐containing epoxy resin (EPN‐D) was prepared by addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and epoxy phenol‐ formaldehyde novolac resin (EPN). The reaction was monitored by epoxide equivalent weight (EEW) titration, and its structure was confirmed by FTIR and NMR spectra. Halogen‐free epoxy resins containing EPN‐D resin and a nitrogen‐containing epoxy resin (XT resin) were cured with dicyandiamide (DICY) to give new halogen‐free epoxy thermosets. Thermal properties of these thermosets were studied by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), thermal mechanical analyzer (TMA) and thermal‐gravimetric analysis (TGA). They exhibited very high glass transition temperatures (T_gs, 139–175°C from DSC, 138–155°C from TMA and 159–193°C from DMA), high thermal stability with T_{d,5 wt %} over 300°C when the weight ratio of XT/EPN‐D is ≥1. The flame‐retardancy of these thermosets was evaluated by limiting oxygen index (LOI) and UL‐94 vertical test. The thermosets containing isocyanurate and DOPO moieties showed high LOI (32.7–43.7) and could achieve UL‐94 V‐0/V‐1 grade. Isocyanurate and DOPO moieties had an obvious synergistic effect on the improvement of the flame retardancy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Development of a DOPO‐containing melamine epoxy hardeners and its thermal and flame‐retardant properties of cured products

In this study, a novel Schiff base of melamine used as flame‐retardant curing agent for epoxy resins, was synthesized via condensation reaction of 4‐hydroxybenzaldehyde with melamine, followed by the addition of 9,10‐dihydro‐9‐oxa‐10‐phosphaphen‐anthrene 10‐oxide (DOPO) to the resulting imine linkage. The structure of DOPO‐containing melamine Schiff base (P‐MSB) was characterized by Fourier transformed infrared spectroscopy, ¹H‐nuclear magnetic resonance (¹H‐NMR) and ³¹P‐NMR. The compound (P‐MSB) was used as a reactive flame retardant in o‐cresol formaldehyde novolac epoxy resin (CNE) to prepare flame‐retardant epoxy resins for electronic application. The thermal and flame‐retardant properties of the epoxy resins cured by various equivalent ratios phenol formaldehyde novolac (PN) and P‐MSB were investigated by the nonisothermal differential scanning calorimetry, the thermogravimetric analysis, and limiting oxygen index test. The obtained results showed that the cured epoxy resins possessed high T_g (165°C) and good thermal stability (T_5%, 321°C). Moreover, the P‐MSB/CNE systems exhibited higher limiting oxygen index (35) and more char was maintained in P‐MSB/CNE systems than that in PN/CNE system and the effective synergism of phosphorus–nitrogen indicated their excellent flame retardancy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improving thermal and flame‐retardant properties of epoxy resins by a novel reactive phosphorous‐containing curing agent

In an attempt to improve thermal and flame‐retardant properties of epoxy resins efficiently, a new reactive phosphorus‐containing curing agent called 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐yl‐(phenylimino)‐(4‐hydroxyphenyl)me‐thane (DOPO‐PHM) was synthesized and was combined with 4,4′‐diaminodiphenyl methane (DDM) to co‐cure epoxy resins (E51), which covalently incorporated halogen‐free DOPO organ groups into the epoxy networks. The chemical structure of this curing agent was confirmed by FTIR, 1D, and 2D NMR spectra. A reaction mechanism during the preparation was proposed, and the electron effect on the stabilization of the carbocation was discussed. Various DDM/DOPO‐PHM molar ratios were used to get the materials with different phosphorus contents. Their dynamic mechanical, thermal, and flame‐retardant properties were evaluated by dynamic mechanical thermal analysis, thermogravimetric analysis, and limiting oxygen index (LOI) respectively. All samples had a single T_g, showing that these epoxy resins were homogeneous phase for long‐term use in spite of adding DOPO‐PHM. Both char yields (under nitrogen and air atmospheres) increased with the increasing of phosphorus content and the LOI values increased from 24.5 for standard resin to 33.5 for phosphorus‐containing resins, indicating the significant enhancement of thermal stability and flame retardancy. POLYM. ENG. SCI., 54:1192–1200, 2014. © 2013 Society of Plastics Engineers     

Synthesis,thermal and mechanical behavior of a silicon/phosphorus containing epoxy resin

A liquid silicon/phosphorus containing flame retardant (DOPO–TVS) was synthesized with 9,10‐dihydro‐9‐oxa‐10‐phosphapheanthrene‐10‐oxid (DOPO) and triethoxyvinylsilane (TVS). Meanwhile, a modified epoxy resin (IPTS–EP) was prepared by grafting isocyanate propyl triethoxysilane (IPTS) to the side chain of bisphenol A epoxy resin (EP) through radical polymerization. Finally, the flame retardant (DOPO–TVS) was incorporated into the modified epoxy resin (IPTS–EP) through sol–gel reaction between the ethyoxyl of the two intermediates to obtain the silicon/phosphorus containing epoxy resin. The molecular structures of DOPO–TVS, IPTS–EP and the final modified epoxy resin were confirmed by FTIR spectra and ¹H‐NMR, ³¹P‐NMR. Thermogravimetric analysis (TGA), differential scanning calorimetry, and limiting oxygen index were conducted to explore the thermal properties and flame retardancy of the synthesized epoxy resin. The thermal behavior and flame retardancy were improved. After heating to 600°C in a tube furnace, the char residue of the modified resin containing 10 wt % DOPO–TVS displayed more stable feature compared to that of pure EP, which was observed both by visual inspection and scanning electron microscope (SEM). Moreover, the mechanical performance testing results exhibited the modified epoxy resins possessed elevated tensile properties and fracture toughness which is supported by SEM observation of the tensile fracture section. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42788.     

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     

Synthesis and liquid oxygen compatibility of a phosphorous‐containing epoxy resin

A phosphorus‐containing epoxy resin was synthesized successfully by 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and bisphenol F epoxy resin (DGEBF) and its molecular structure was confirmed by FTIR spectra. The results of the liquid oxygen mechanical impact test indicated that the cured phosphorus‐containing epoxy resin did not show any reactions during the 20 times of mechanical impact, which revealed that it was compatible with liquid oxygen. Thermal properties of the cured epoxy resins were evaluated by differential scanning calorimetry and thermal gravimetric analysis. It was found that the cured phosphorus‐containing epoxy resin had a better thermal stability than DGEBF. The enhancement of thermal stability for the epoxy resin was favorable to improve liquid oxygen compatibility. The X‐ray photoelectron spectroscopy analysis confirmed that the mechanical impact resulted in phosphorus‐containing groups on the surface of the cured phosphorus‐containing epoxy resin thermally decomposed to form phosphoric oxyacid which was in accordance with the mechanism that organo‐phosphorus compounds could work in the condensed phase to inhibit the combustion. These results suggest that the phosphorus‐containing epoxy resin has the potential as the matrix of the liquid oxygen composite tank. POLYM. ENG. SCI., 55:651–656, 2015. © 2014 Society of Plastics Engineers     

Phosphorous‐containing epoxy resins from a novel synthesis route

The ? P(O)‐H in 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) was used as an active group to react with the carbonyl group in 4,4′‐dihydroxybenzophenone (DHBP) to result a novel phosphorous‐containing biphenol compound (DOPO‐2OH). Phosphorous‐containing epoxy resins were therefore obtained from reacting DOPO‐2OH with epichlorohydrin or with diglycidylether bisphenol A. The synthesized compounds were characterized with FTIR, ¹H and ³¹P NMR, elemental analysis, and epoxide equivalent weight titration to demonstrate the their chemical structures. Cured epoxy resins were prepared via thermal curing the epoxy resins with various curing agents. Thermal analysis results (differential scanning calorimetry and thermogravimetric analysis) revealed that these cured epoxy resins exhibited high glass transition temperatures and high thermal stability. High char yields at 700°C and high LOI (limited oxygen index) values were also found for the cured epoxy resins to imply that the resins were possessing high flame retardancy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1697–1701, 2002     

Synthesis of phosphorus‐containing polyhedral oligomeric silsesquioxanes via hydrolytic condensation of a modified silane

A simple route to synthesize a new type of phosphorus‐containing polyhedral oligomeric silsesquioxanes (DOPO–POSS) in high yield, by the hydrolytic condensation of a modified silane, is reported. The starting material was a phosphorus‐containing triethoxy silane (DOPO–VTES), which was synthesized by addition reaction between 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and vinyl triethoxy silane (VTES). This product was subjected to hydrolytic condensation using an HCl catalyst in methanol. The new types of phosphorus‐containing POSS were obtained and characterized using ¹H, ¹³C, ²⁹Si‐NMR, MALDI‐TOF MS, XRD, DSC, and FTIR. All of these results suggested that the DOPO–POSS were amorphous mixtures of T₈, T₉(OH), and TGA curve of DOPO–POSS shows that the cage‐like compound has high thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of halogen-free flame retardant epoxy resins with phosphorus-containing siloxanes

Novel epoxy resin modifiers, DOPO–TMDS and DOPO–DMDP were synthesized by addition reaction of divinylsiloxane with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Halogen-free flame retardant epoxy resins were obtained through modification of o-cresol novolac epoxy resin cured by phenol novolac resin using DOPO–TMDS and DOPO–DMDP which were characterized by ¹H NMR, ¹³C NMR, ³¹P NMR and FT-IR measurements. Effects of the phosphorus-containing siloxanes on thermal stabilities, mechanical properties and flame retardant properties of the epoxy resins were investigated. The cured epoxy resins exhibited better mechanical properties and greatly improved flame retardant properties due to the presence of phosphorus-containing siloxanes. The cured epoxy resins with phosphorus loading of 2.0 wt% showed LOI values of 32–33 and achieved UL94V-0 ratings.     

Synthesis and properties of phosphorus‐containing advanced epoxy resins. II

Two phosphorus‐containing diacids were synthesized from 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and either maleic acid or itaconic acid and then reacted with diglycidyl ether of bisphenol A (DGEBA) to form two series of advanced epoxy resins. Reaction conditions, such as reaction time, temperature and catalyst, are discussed in this article. After curing with 4,4'‐diaminodiphenyl sulfone (DDS), thermal properties of cured epoxy resins were studied using dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA). The flame retardancy of cured epoxy resins was evaluated using a UL‐94 measurement. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 228–235, 2000     

Synthesis and properties of novel phosphorus‐containing bismaleimide/epoxy resins

A novel soluble phosphorus‐containing bismaleimide (BMI) monomer, bis(3‐maleimidophenyl)phenylphosphine oxide (BMIPO), was synthesized by the imidization of bis(3‐aminophenyl) phenylphosphine oxide, in which its structural characterization was identified with ¹H‐NMR, ¹³C‐NMR, and Fourier transform infrared spectra. The BMIPO resin, with five‐membered imide rings and high phenyl density, was an excellent flame retardant with a high glass‐transition temperature (T_g), onset decomposition temperature, and limited oxygen index. In phosphorus‐containing BMI/epoxy/4,4′‐methylene dianiline (DDM)‐cured resins, homogeneous products were obtained from all proportions without phase separation. Because of the higher reactivity of BMIPO/DDM relative to that of 4,4′‐bismaleimidodiphenylmethane (BMIM)/DDM, the increase in the BMIPO/BMIM ratio in this blending resin increased the recrosslinking hazards of the postcuring stage and so lowered the T_g value and thermal stability. The thermal stability of the BMI/epoxy‐cured system was lower than that of the epoxy‐cured system because of the introduction of a phosphide group into BMIPO, whereas for the T_g value and flame retardancy, the former was significantly higher than the latter: the higher the BMIPO content in the blend, the higher the flame retardancy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2080–2089, 2002; DOI 10.1002/app.10607     

Improving thermal and flame‐retardant properties of epoxy resins by a new imine linkage phosphorous‐containing curing agent

A new reactive phosphorus‐containing curing agent with imine linkage called 4, 4′‐[1, 3‐phenyl‐bis(9, 10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐yl)dimethyneimino)]diphenol (2) was synthesized both via two‐pot and one‐pot procedure. The chemical structure of this curing agent was confirmed by FTIR, ¹H, ¹³C, and ³¹P NMR spectra. A series of thermosetting systems were prepared by using conventional epoxy resins (E51), 4, 4′‐diaminodiphenyl methane (DDM) and (2). Resins with different phosphorus contents were obtained by changing the DDM/(2) molar ratios. Their dynamic mechanical thermal, thermal and flame‐retardant properties were evaluated by dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), and limiting oxygen index (LOI), respectively. All samples had a single T_g, which showed that these epoxy resins were homogeneous phase. Both the two char yields under nitrogen and air atmospheres increased with increasing content of (2) and the LOI values increased from 24.5 for standard resin to 37.5 for phosphorus‐containing resin, which indicated that incorporation of (2) could impart good thermal stability and excellent flame retardancy to the conventional epoxy thermosets. POLYM. ENG. SCI., 56:441–447, 2016. © 2016 Society of Plastics Engineers     

Effect of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide on liquid oxygen compatibility of bisphenol a epoxy resin

In this study, bisphenol A epoxy resin (DGEBA) was chemically modified by 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), and the molecular structure of the modified epoxy resin was characterized by Fourier transform infrared spectra. The effects of DOPO on liquid oxygen compatibility of DGEBA were calculated using mechanical impact method. The results indicated that epoxy resin (EP‐P1)/4,4‐diaminobisphenol sulfone (DDS) was compatible with liquid oxygen. When compared with EP/DDS, differential scanning calorimetry and thermogravimetry analyses showed that EP‐P1/DDS and EP‐P2/DDS had much higher glass transition temperatures and char yield. X‐ray photoelectron spectroscopic analysis suggested that phosphorus atoms on the surface of EP‐P1/DDS and EP‐P2/DDS could act in the solid phase to restrain the incompatible reaction, which was in accordance with the flame‐retardant mechanism of phosphorus‐containing compounds. The compatibility mechanism of EP‐P1/DDS was further proposed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40848.     

Synthesis,thermal properties,and flame retardance of the epoxy‐silsesquioxane hybrid resins

Epoxy/silsesquioxane‐OH (EP‐SDOH, ED) hybrid resins were prepared from cyclohexyl‐disilanol silsesquioxane (SDOH) and diglycidyl ether of bisphenol A via the reaction between silanol and the oxirane group, with the cobalt naphthanate as a catalyst. It was found that incorporation of SDOH allows the reaction between oxirane ring and Si? OH, and the silsesquioxane cage structure can be the main chain or as the side chain of the hybrid resin. The EP‐SDOH hybrid resins with various SDOH contents were cured by 4,4′‐diaminodiphenylsulphone, and the curing reaction was investigated by differential scanning calorimetry. The curing characteristics of EP‐SDOH hybrids had been observed to be influenced by the content of SDOH in the hybrid. The differential scanning calorimetry thermograms indicated that the EP‐SDOH hybrid exhibited a higher initial temperature, peak temperature, as well as final temperature than those of the pure epoxy resin when cured by the same curing agent 4,4′‐diaminodiphenylsulphone. The curing kinetic parameters were calculated by using the Ozawa method and the results indicated that EP‐SDOH hybrids possess the same curing mechanism as the pure epoxy resin. The properties of the cured EP‐SDOH hybrid resins such as the glass transition temperature (T_g), dynamic mechanical analysis, thermal stability, as well as the flame retardance were also investigated, and the results showed that introducing silsesquioxane‐OH unit into epoxy resin successfully modified the local structure, made the chain stiffness, restrict the chain mobility, and eventually improved thermal stability and flame retardance of epoxy resin. POLYM. ENG. SCI., 47:225–234, 2007. © 2007 Society of Plastics Engineers.     

Studies on UV‐stable silicone–epoxy resins

Silicone–epoxy resins were synthesized through hydrosilylation of 1,2‐epoxy‐4‐vinyl‐cyclohexane with 1,3,5,7‐tetramethycyclotetrasiloxane. The silicone–epoxy resins showed high reactivity in the presence of aluminum complex/silanol compound catalysts. Curing of the resins was effected at extremely low concentrations of the aluminum acetylacetonate/Ph₂Si(OH)₂ catalyst to give hard materials with optical clarity. For the silicone–epoxy resins containing Si? H bonds, Al(acac)₃ alone is effective for the curing. The cured silicone–epoxy resins showed excellent UV resistance. An improvement in the lifetime of UV‐LEDs was achieved using the silicone–epoxy compositions as encapsulant. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3954–3959, 2007     

Flame retardancy effects of phosphorus‐containing compounds and cationic photoinitiators on photopolymerized cycloaliphatic epoxy resins

This study presents a promising ultraviolet (UV)‐curable epoxy resin formulation with improved flame‐retardant properties. The formulation is based on the cycloaliphatic epoxide 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane carboxylate (ERL4221) and a novel silicon, phosphorous containing flame‐retardant additive. The additive, 1,3,5,7‐tetramethyl‐1,3,5,7‐tetra 2‐(6‐oxido‐6‐H‐dibenzo(c,e) (1,2)oxaphosphorin‐6‐yl) ethylcyclotetrasiloxane (DOPO‐SiD), was synthesized by the addition reaction of 1,3,5,7‐tetramethyl‐1,3,5,7‐tetravinylcyclotetrasiloxane (D₄Vi) with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO). Formulations containing the cycloaliphatic epoxy resin ERL4221 and the flame‐retardant DOPO‐SiD additive were prepared in various concentrations and crosslinked by UV irradiation. The effects of DOPO‐SiD and photoinitiators, such as the cyclopentadienyl iron complex of carbazole (In‐Fe) and diphenyl‐(4‐(phenylthiol) phenyl) sulfonium hexafluorophosphate (In‐S), on the flame‐retardant properties and thermal stabilities of UV‐cured ERL4221/DOPO‐SiD composites were investigated with limiting oxygen index, UL‐94 vertical test, and thermogravimetric analysis, respectively. The results showed that DOPO‐SiD can increase the thermal stabilities of the ERL4221/DOPO‐SiD. The char yield was improved when DOPO‐SiD and In‐Fe were simultaneously used. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40011.     

Study on the modification of epoxy resin by a phosphorus‐ and silica‐containing hybrid

A novel phosphorus‐ and silica‐containing hybrid (DPS) was synthesized by the reaction between diethyl phosphate (DEP) and polyhedral oligomeric siloxanes (POS) formed by hydrolysis condensation of 3‐glycidoxypropyltrimethoxysilane (GPTMS). The novel phosphorus‐ and silica‐containing hybrid was characterized by the flourier transform infrared spectroscope (FT‐IR), silicon nuclear magnetic resonance, and gel permeation chromatography (GPC). Then, the determination of the activation of the reaction between epoxy resin and phosphorus‐, and silica‐containing hybrids was studied by differential scanning calorimeter (DSC). In the presence of catalyst, the activation energies of the curing reaction were 63.3 and 66.7 kJ/mol calculated by Kissinger model and Ozawa model respectively. The thermal and flame retardant properties of the cured epoxy modified by DPS were determined by differential scanning calorimeter (DSC), thermal gravimetric analysis (TGA), and limited oxygen index (LOI). The results revealed that those properties were improved in comparison with unmodified epoxy resin. In addition, scanning electron microscopy (SEM) was used to investigate the morphology of the cured epoxy resin modified by DPS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of organo‐phosphorus and nano‐clay materials on the thermal and fire performance of epoxy resins

The results of flame retardance and thermal stability of a reactively modified organo‐phosphorus diglycidylether of bisphenol‐A and an organo‐phosphorus tetraglycidyl diaminodiphenylmethane are reported here. The organo‐phosphorus epoxy resins were synthesized by the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and diglycidyl ether of bisphenol‐A and tetraglycidyl diaminodiphenylmethane, respectively, and then cured with a mixture of 3,5‐diethyltoluene‐2,4‐diamine and 3,5‐diethyltoluene‐2,6‐diamine. In addition to this, between 5 and 7.5% of organically modified polymeric layered silicate nano‐clay was also added to neat epoxy resin or to the phosphorus‐modified epoxy resin to investigate any synergies, or otherwise, a combination of clay and phosphorus on the flame, degradation, and thermal properties are also reported. The reaction kinetics of phosphorus‐modified and epoxy cure were studied by FTIR, ¹H‐NMR, and DSC. Thermal properties and morphology of the final product were analyzed by thermogravimetric analysis, dynamic mechanical thermal analysis, X‐ray diffraction, and cone calorimetry. Improvement in flame retardance by cone calorimetry was demonstrated by the addition of only 3% phosphorus or 7.5% clay into the epoxy compared with unmodified epoxy resins, whereas no evidence of synergy for a phosphorus and clay combination was found. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1233–1253, 2004     

Phosphorus‐containing terephthaldialdehyde adducts—Structure determination and their application as flame retardants in epoxy resins

Two novel phosphorus‐rich prepolymers based on epoxy novolac and terephthaldialdehyde and potential flame retardants, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and 2,8‐dimethyl‐phenoxaphosphin‐10‐oxide (DPPO) were synthesised. The resultant flame‐retardant epoxy resins were cured with 4,4′‐diaminodiphenylmethane (DDM) and 4,4′‐diamino‐dicyclohexylmethane (PACM). Their flammability and burning behavior were characterised by UL 94 and LOI and compared with analogue prepolymers based on diethylphosphite (DEPP). The glass transition temperatures were determined by DSC measurements. Furthermore, the structures of two exemplary molecules based on p‐tolylaldehyde adducts were examined by XRD and NMR analysis to determine the possibilities of linking the two novel DOPO and DPPO derivatives to the backbone of the epoxy resin. Additionally, the char yields were determined by TG analysis and thermal desorption mass spectroscopy of the thermosets used and compared with each other to obtain more information about the possible mode of flame‐retardant action of the different phosphorus compounds. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008