Synthesis and properties of flame‐retardant benzoxazines by three approaches

We propose three approaches to obtain flame‐retardant benzoxazines. In the first approach, we synthesize a novel benzoxazine (dopot‐m) from a phosphorus‐containing triphenol (dopotriol), formaldehyde, and methyl amine. Dopot‐m is copolymerized with a commercial benzoxazine [6′,6‐bis(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazineyl)methane (F‐a)] or diglycidyl ether of bisphenol A (DGEBA). The thermal properties and flame retardancy of the F‐a/dopot‐m copolymers increase with the content of dopot‐m. As for the dopot‐m/DGEBA curing system, the glass‐transition temperature of the dopot‐m/DGEBA copolymer is 252 °C, which is higher than that of poly(dopot‐m). The 5% decomposition temperature of the dopot‐m/DGEBA copolymer increases from 323 to 351 °C because of the higher crosslinking density caused by the reaction of phenolic OH and epoxy. In the second approach, we incorporate the element phosphorus into benzoxazine via the curing reaction of dopotriol and F‐a. After the curing, the thermal properties of the F‐a/dopotriol copolymers are almost the same as those of neat poly(F‐a), and this implies that we can incorporate the flame‐retardant element phosphorus into the polybenzoxazine without sacrificing any thermal properties. In the third approach, we react dopo with electron‐deficient benzoxazine to incorporate the element phosphorus. After the curing, the glass‐transition temperatures of polybenzoxazines decrease slightly with the content of dopo, mainly because of the smaller crosslinking density of the resultant polybenzoxazines. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3454–3468, 2006     

Advanced flame‐retardant epoxy resins from phosphorus‐containing diol

Phosphorus‐containing epoxy systems were prepared from isobutylbis(hydroxypropyl)phosphine oxide (IHPO) and diglycidyl ether of bisphenol A (DGEBA). Diethyl‐N,N‐bis(2‐hydroxyethyl) aminomethyl phosphonate (Fyrol 6) could not be incorporated into the epoxy backbone by a reaction with either epichlorohydrin or DGEBA because intramolecular cyclization took place. The curing behavior of the IHPO–DGEBA prepolymer with two primary amines was studied, and materials with moderate glass‐transition temperatures were obtained. V‐0 materials were obtained when the resins were tested for ignition resistance with the UL‐94 test. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3510–3515, 2005     

A novel intumescent flame‐retardant LDPE system and its thermo‐oxidative degradation and flame‐retardant mechanisms

A carbonization agent, 3,9‐di (2‐hydroxyisopropyl)‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro‐[5,5]‐undecane (SPEPO), was synthesized from pentaerythritol (PER), phosphorus trichloride, formic acid, and acetone as raw materials. The structure of SPEPO was characterized by FTIR and ¹H‐NMR. As a carbonization agent and an acid source, SPEPO can form a novel intumescent flame‐retardant (IFR) system for low density polyethylene (LDPE) together with ammonium polyphosphate (APP) and melamine phosphate (MP). The flame retardancy and thermal behavior of the IFR system for LDPE were investigated by limiting oxygen index (LOI), UL‐94 test, and thermogravimetric analysis (TGA). When the weight ratio of SPEPO, APP, and MP is 7:7:1 and their total loading level is 30%, the IFR‐LDPE presents the optimal flame retardancy (LOI value of 27.6 and UL‐94 V‐0 rating). However, SPEPO, APP, or MP can only show a very poor flame‐retardant performance when used alone. This indicates that there is a synergistic effect among SPEPO, APP, and MP. TGA results obtained in air demonstrate that SPEPO has an ability of char formation itself, and the char residue of SPEPO can reach 24 wt% at 700°C. The IFR can change the thermal degradation behavior of LDPE, enhance T_max of the decomposition peak of LDPE, and promote LDPE to form char based on the calculated and the experimental data of residues. According to the results of Py‐GC/MS in combination with FTIR of the char residues at different temperatures, a possible flame‐retardant mechanism has been proposed. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermally stable and flame‐retardant aromatic phosphate and cyclotriphosphazene‐containing polyurethanes: synthesis and properties

A novel flame retardant (4‐diphenylphosphoryloxyphenoxy)(4‐hydroxyphenoxy)cyclotriphosphazene (PPPZ) was prepared and characterized by FT‐IR, ³¹P‐NMR and ¹H‐NMR spectroscopy. Polyurethanes that contained aromatic phosphate groups attached to cyclotriphosphazene, with various phosphorus contents, were prepared from PPPZ, poly(propylene glycol), 1,4‐butanediol, and 2,4‐toluene diisocyanate by one‐step polymerization. The polymers prepared were characterized by FT‐IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and oxygen index (LOI) measurements. The effect of the concentration of PPPZ on the thermal behavior of the polyurethane was studied. The results indicated that the glass transition temperature (T_g) of the polyurethane increased with the concentration of PPPZ. The PPPZ‐containing polyurethanes exhibited slightly higher temperatures of degradation and higher char yields than PPPZ‐free polyurethanes. Moreover, the LOI of the polyurethanes increased with increasing PPPZ content. Also studied was the possible mechanism of the flame retardancy. Copyright © 2005 John Wiley & Sons, Ltd.     

Facile,one‐pot synthesis of aromatic diamine‐based phosphinated benzoxazines and their flame‐retardant thermosets

Three aromatic diamine‐based, phosphinated benzoxazines ( 7–9 ) were prepared from three typical aromatic diamines—4,4′‐diamino diphenyl methane ( 1 ), 4,4′‐diamino diphenyl sulfone ( 2 ), and 4,4′‐diamino diphenyl ether ( 3 ) by a one‐pot procedure. To clarify the reaction mechanism, a two‐pot procedure was applied, in which the reaction intermediates ( 4–6 ) were isolated for characterization. The structures of intermediates and benzoxazines were confirmed by high resolution mass, IR, and 1D and 2D‐NMR spectra. In addition to self‐polymerization, ( 7–9 ) were copolymerized with cresol novolac epoxy (CNE). After curing, the homopolymers of P( 7–9 ) are brittle while the copolymers of ( 7–9 )/CNE are tough. Dynamic mechanical analysis shows the T_gs of ( 7–9 )/CNE copolymers are 187, 190, and 171 °C, respectively. Thermal mechanical analysis shows the CTEs of ( 7–9 )/CNE copolymers are 46, 38, and 46 ppm, respectively. All the ( 7–9 )/CNE copolymers belong to an UL‐94 V‐0 grade, demonstrating good flame retardancy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Development of novel flame‐retardant thermosets based on boron‐modified phenol–formaldehyde resins

Boron‐containing novolac resins were prepared through the modification of a commercial novolac resin with different contents of bis(benzo‐1,3,2‐dioxaborolanyl) oxide. Their thermal and flame‐retardant properties were measured. Then, they were crosslinked with hexamethylenetetramine, and their thermal, thermodynamomechanical, and flame‐retardant properties were evaluated. Their modification degree was related to the segmental motion of the materials. The crosslinking of the boron‐modified novolac resins with hexamethylenetetramine was slower and not as extensive as that of commercial novolac resins because the nitrogen from intermediate species coordinated with boron. The thermal degradation of the boron‐containing novolac resins generated boric acid at high temperatures and gave an intumescent char that slowed the degradation and prevented it from being complete. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3503–3512, 2006     

The synthesis and properties of a reactive flame‐retardant unsaturated polyester resin from a phosphorus‐containing diacid

A transparent flame‐retardant unsaturated polyester resin (FR‐UPR) was obtained by reacting propylene glycol (PG) with maleic anhydride (MA), phthalic anhydride (PA), and 9,10‐dihydro‐10[2,3‐di(hydroxy carbonyl)propyl]‐10‐phosphaphenanthrene‐10‐oxide (DDP) synthesized from 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and itaconic acid (ITA). The chemical structure of the resulting FR‐UPR was confirmed by FTIR, ¹H‐NMR and ³¹P‐NMR. The average molecular weight and viscosity of the FR‐UPR were determined by gel permeation chromatography (GPC) and viscometer, respectively. Thermal stability was studied by thermogravimetric analysis (TGA) both in air and nitrogen to determine the thermal decomposition mechanism, and the apparent activation energy (E_a) was calculated by both the Kissinger and Ozawa methods. Compared to unsaturated polyester resin (UPR), the higher E_a of FR‐UPR3 implied an improved thermal stability. According to variations of the limited oxygen index (LOI) values, the UL 94 rating of vertical burning test and scanning electron microscopy (SEM) photographs of char residues, the flame retardance of cured FR‐UPR was enhanced with increasing DDP content. The study of fire reaction tests, using a cone calorimeter, suggested that there was a significant reduction of flammability in the FR‐UPR. Copyright © 2010 John Wiley & Sons, Ltd.     

Photocrosslinking and related properties of intumescent flame‐retardant LLDPE/EVA/IFR blends

The photoinitiated crosslinking of halogen‐free flame retarded linear low density polyethylene/poly(ethylene‐co‐vinyl acetate) blends (LLDPE/EVA) with the intumescent flame retardant (IFR) of phosphorous‐nitrogen compound (NP) in the presence of photoinitiator and crosslinker and their characterization of related properties have been investigated by gel determination, heat extension test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), Fourier transfer infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), mechanical properties measurements, limiting oxygen index (LOI), UL‐94, and water resistance test. The data from the gel content and heat extension rate (HER) show that the LLDPE/EVA/IFR blends filled with NP are readily crosslinked to a gel content of above 75% and the HER values reach about 50% by UV‐irradiation of 5 sec under suitable amount of photoinitiator and crosslinker. The data obtained from the CCT and LOI indicate that photocrosslinking can considerably decrease the heat release rates (HRR) by 10–15%, prolongate the combustion time, and increase two LOI values for the LLDPE/EVA/NP blends UV irradiated for 5 sec. The results from TGA and the dynamic FTIR spectra give the evidence that the photocrosslinked LLDPE/EVA/NP samples show slower thermal degradation rate and higher thermo‐oxidative degradation temperature than the uncrosslinked LLDPE/EVA/NP samples. The morphological structures of charred residues observed by SEM give the positive evidence that the compact charred layers formed from the photocrosslinked LLDPE/EVA/NP samples play an important role in the enhancement of flame retardant and thermal properties. The data from the mechanical tests and water‐resistant measurements show that photocrosslinking can considerably improve the mechanical and water‐resistant properties of LLDPE/EVA/NP samples. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of novel flame‐retardant thermosets based on benzoxazine–phenolic resins and a glycidyl phosphinate

Modified novolac resins with benzoxazine rings were prepared and copolymerized with a glycidyl phosphinate. Their curing behavior and the thermal properties of the curing resins were studied. Copolymerization was studied with model compounds considering the functionality of the benzoxazine‐based phenolic resins and the easy isomerization of the glycidyl phosphinate. Phenolic novolac resin acts as an initiator but p‐toluensulfonic acid had to be used to decrease the curing temperature and to prevent glycidyl phosphinate from isomerizing. The materials obtained exhibited high glass‐transition temperatures and retardation on thermal degradation rates. V‐0 materials were obtained when the materials were tested for ignition resistance with the UL‐94 test. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 279–289, 2004     

Synthesis and flame retardant potential of polyols based on bisphenol‐S

Polyether polyols based on bisphenol‐S were prepared by alkoxylation and compared with analogs based on bisphenol‐A, as well as standard aromatic polyester, and polyether polyols for viscosity and temperature stability. Thermo‐oxidative stability was determined by thermo‐gravimetric analysis, pyrolysis gas chromatography/mass spectroscopy, and evolved gas analysis mass spectroscopy. Incorporation of the sulfone moiety was found to dramatically improve the thermo‐oxidative stability of the neat polyol. Significant char formation was observed with gas phase evolution of flame retardant SO₂ and aromatic sulfone only apparent at about 600 °C. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2102–2108     

A flame‐retardant phosphate and cyclotriphosphazene‐containing epoxy resin: Synthesis and properties

A novel flame‐retardant epoxy resin, (4‐diethoxyphosphoryloxyphenoxy)(4‐glycidoxyphenoxy)cyclotriphosphazene (PPCTP), was prepared by the reaction of epichlorohydrin with (4‐diethoxyphosphoryloxyphenoxy)(4‐hydroxyphenoxy)cyclotriphosphazene and was characterized by Fourier transform infrared, ³¹P NMR, and ¹H NMR analyses. The epoxy resin was further cured with diamine curing agents, 4,4′‐diaminodiphenylmethane (DDM), 4,4′‐diaminodiphenylsulfone (DDS), dicyanodiamide (DICY), and 3,4′‐oxydianiline (ODA), to obtain the corresponding epoxy polymers. The curing reactions of the PPCTP resin with the diamines were studied by differential scanning calorimetry. The reactivities of the four curing agents toward PPCTP were in the following order: DDM > ODA > DICY > DDS. In addition, the thermal properties of the cured epoxy polymers were studied by thermogravimetric analysis, and the flame retardancies were estimated by measurement of the limiting oxygen index (LOI). Compared to a corresponding Epon 828‐based epoxy polymer, the PPCTP‐based epoxy polymers showed lower weight‐loss temperatures, higher char yields, and higher LOI values, indicating that the epoxy resin prepared could be useful as a flame retardant. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 972–981, 2000     

Mechanical and flame‐retardant properties of biodegradable polylactide composites with hyperbranched silicon‐containing polymer

A hyperbranched polymer (HBP‐B2) containing siloxane chains was synthesized via bulk polymerization of diepoxide with a primary amine in the presence of monoepoxide. The weight‐average molecular weight of the prepared polymers was approximately 9200. Composites of polylactide (PLA) with aluminum trihydroxide (ATH) and the HBP‐B2 were prepared via direct melt compounding using a brabender. The test results showed that the LOI could be raised to 34% for the PLA composite with 25 wt% ATH and 5% HBP‐B2. The surface thermal profile of the composite during UL94 V test was further captured by an infrared camera, which was helpful to understand the flame‐retardant properties of the different samples. A V‐0 rating could be achieved by adding ATH and HBP‐B2 to the PLA matrix. Incorporation of HBP‐B2 as a plasticizer could increase the impact strength of a PLA blend or composite. For example, an addition of 10 wt% of HBP and 20 wt% ATH increased the elongation at break from 5% for neat PLA to 155% for the PLA composite.     

Effects of metal oxides on intumescent flame‐retardant polypropylene

Variable amounts of transition metal oxides (MO), such as MnO₂, ZnO, Ni₂O₃, etc., were incorporated into blends of polypropylene (PP)/ammonium polyphosphate (APP)/dipentaerythritol (DPER) with the aim of studying and comparing their effects with main‐group MO on intumescent flame retardance (IFR). The PP/IFR/MO composites were prepared using a twin‐screw extruder, and the IFR behavior was evaluated through oxygen index and vertical burning tests. The progressive enhancement of flame retardancy has proved to be strongly associated with the interaction between APP and MO. With the aid of thermogravimetry (TG) analysis, Fourier transform infrared (FTIR) spectra and scanning electron microscopy, Ni₂O₃ has been shown to be the most effective among the aforementioned three MO. The flame‐retardant mechanism of the IFR system is also discussed in terms of catalytic charring, which relates to complex formation through the d‐orbitals of the transition metal elements. It is considered that the melt viscosity of a PP/APP/DPER blend containing Ni₂O₃ corresponds well to the gas release with increasing temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

The synergistic flame‐retardant effect of O‐MMT on the intumescent flame‐retardant PP/CA/APP systems

The flame retardancy of a novel intumescent flame‐retardant polypropylene (IFR‐PP) system, which was composed of a charring agent (CA), ammonium polyphosphate (APP), and polypropylene (PP), could be enhanced significantly by adding a small amount (1.0 wt%) of an organic montmorillonite (O‐MMT). The synergistic flame‐retardant effect was studied systematically. The thermal stability and combustion behavior of the flame‐retarded PP were also investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical burning test (UL‐94), scanning electronic microscopy (SEM), and cone calorimeter test (CCT). TGA results demonstrated that the onset decomposition temperatures of IFR‐PP samples, with or without O‐MMT, were higher than that of neat PP. Compared with IFR‐PP, the LOI value of IFR‐PP containing 1.0 wt% O‐MMT was increased from 30.8 to 33.0, and the UL‐94 rating was also enhanced to V‐0 from V‐1 when the total loading of flame retardant was the same. The cone calorimeter results showed that the IFR‐PP with 1.0 wt% of O‐MMT had the lowest heat release rate (HRR), total heat release (THR), total smoke production (TSP), CO production (COP), CO₂ production (CO₂P), and mass loss (ML) of all the studied IFR‐PP samples, with or without O‐MMT. All these results indicated that O‐MMT had a significantly synergistic effect on the flame‐retardancy of IFR‐PP at a low content of O‐MMT. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and thermal properties of a novel core‐shell structure flame‐retardant copolymer

In order to improve the flame retardancy of polystyrene (PS), a phosphorus and nitrogen comonomer, named AC₂NP₂, was synthesized and then incorporated into various amounts of PS by seeded emulsion polymerization. The modified methacrylate (AC₂NP₂) was used as the core phase, the styrene as the shell phase, then flame‐retardant effect copolymers with core‐shell structure were prepared successfully. The particle size was ranged from 40 to 60 nm, and the structure and properties of the copolymers were characterized in detail. Notably, despite a few amounts of the AC₂NP₂ units in the copolymers, all the copolymers exhibited significantly enhanced thermal stability and reduced flammability as compared with pure PS. Furthermore, from differential scanning calorimetry test, it was observed that the glass transition temperature was tinily influenced with the incorporation of commoner. The incorporation of P‐N comonomer into PS backbone did not lead to negative effect on the glass transition behavior of PS.     

Crystallization and flame‐retardant properties of polylactic acid composites with polyhedral octaphenyl silsesquioxane

To develop environmental‐friendly and flame‐retarded polymer composites, bio‐based polylactic acid (PLA) was loaded with thermally stable polyhedral octaphenyl silsesquioxane (OPS). Pure PLA and PLA/OPS composites with the OPS of 1, 3, 5, and 10 wt% were prepared by extrusion and injection molding, respectively. The scanning electron microscopy (SEM), polarized optical microscope (POM), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and thermal gravimetric analysis (TGA) were used to analyze the dispersion of the OPS in the PLA matrix and the effects of OPS on the crystallization and thermal stability properties of PLA/OPS composites, respectively. Limited oxygen index (LOI) and cone calorimeter (CONE) measurements were used to study flame retardancy of PLA and PLA/OPS composites. In order to study the flame‐retardant mechanism, the char residues were investigated by SEM, Fourier transform infrared spectra (FTIR), and X‐ray photoelectron spectroscopy (XPS). TGA‐FTIR was used to analyze the gaseous products of their thermal decomposition. The results show that the OPS particles were submicron in the PLA and could increase the crystallization rate of PLA and form small‐sized secondary α‐form crystalline compared with the pure PLA spherulite. The PLA and OPS decomposed individually in the PLA/OPS composites by TGA. According to the LOI tests, the PLA with the OPS loading exhibited very small reduction of LOI. However, the CONE tests indicated that the OPS could improve the flame retardancy of the PLA by means of low peak heat release rate and average heat release rate. It was obtained that the degree and type of the PLA crystalline for the pure PLA and PLA/OPS affect their flame retardancy. In the max thermal decomposition stage of PLA and PLA/OPS, their gaseous products were similar; at high temperatures, the PLA/OPS produced simple and clear gaseous products of PLA with solid SiO₂ in the gas phase.     

Highly efficient multielement flame retardant for multifunctional epoxy resin with satisfactory thermal,flame‐retardant,and mechanical properties

Multifunctional epoxy resins with excellent, thermal, flame‐retardant, and mechanical properties are extremely important for various applications. To solve this challenging problem, a novel highly efficient multielement flame retardant (PMSBA) is synthesized and the flame‐retardant and mechanical properties of modified epoxy resins are greatly enhanced without significantly altering their and thermal properties by applying the as‐synthesized PMSBA. The limiting oxygen index value reaches up to 29.6% and could pass the V‐0 rating in the UL‐94 test with even low P content (0.13%). Furthermore, cone calorimetry results demonstrate that 30.3% reduction in the peak heat release rate for the sample with 10.0 wt% PMSBA is achieved. X‐ray photoelectron spectroscopy and scanning electron microscopy indicate that Si‐C, Si‐N, and phosphoric acid derivative can be transformed into a multihole and intumescent char layer as an effective barrier, preserving the epoxy resin structure from fire. More importantly, mechanical properties such as impact strength, tensile strength, and flexural strength are also increased by 63.86%, 33.54%, and 15.65%, respectively, which show the incorporation of PMSBA do not deteriorate the mechanical properties of modified epoxy resins. All the results show that PMSBA is a promising strategy for epoxy resin with satisfactory, thermal, flame‐retardant, and mechanical properties.     

Flame retardant high oleic sunflower oil‐based thermosetting resins through aza‐ and phospha‐michael additions

Phosphorus‐containing thermosetting resins derived from high oleic sunflower oil were prepared through phospha‐Michael addition of a difunctional secondary phosphine oxide, the 1,3‐bis(phenylphosphino)propane dioxide on the α,β‐unsaturated ketone derived from high oleic acid (ETR). The aim of this approach was to introduce phosphorus and to crosslink the material in one single step. Materials with increasing aromatic content were also prepared by addition 4,4′‐diaminodiphenylmethane and co‐crosslinking through aza‐Michael addition. The kinetics of the phospha and aza‐Michael additions was investigated using the enone derivative of methyl oleate (EO) in presence of BF₃·Et₂O as catalyst and in absence of catalyst at different temperatures. Competitive experiments showed that phospha‐Michael addition proceeds faster than the aza‐Michael addition. The new triglyceride‐based thermosets containing up to 4.2% of P, were characterized and their thermal and flame retardant properties evaluated. Limiting oxygen index values increase from 21.5 for the phosphorus free material up to 38.0 for the final material with 4.2% P content. These results demonstrate that the flame retardant properties of vegetable oil‐based thermosets can be significantly improved by adding covalently bonded phosphorus to the polymer. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of chalcone‐containing methacrylate‐based hydrogen bonded side chain liquid crystalline polymer and its dielectric properties

In this work, a new methacrylate‐based hydrogen bonded side chain liquid crystalline polymer having chalcone moieties (HBCP) was prepared from poly(4‐(3‐(pyridin‐4‐yl)acryloyl) phenyl methacrylate) and 11‐(4‐cyanobiphenyl‐4(‐oxy) undekan‐1‐ol (LC11)) by molecular self‐assembly processes via hydrogen bond formation between nitrogen of the HBCP and hydroxyl group of the LC11. The formation of H bond was confirmed by using Fourier transform infrared (FTIR) spectroscopy. The phase transition temperatures and liquid crystalline phases of the HBCP were examined by DSC and POM measurements. The dielectric properties of HBCP have been determined by impedance analyzer within the frequency interval of 100 Hz–15 MHz. According to Cole–Cole plot, the equivalent circuit of the LC system has been found as a capacitor in parallel with a resistor. The resonance frequency, f_r, of the R–C circuit has also been calculated as 1.59 MHz by phase angle versus frequency curve. The dielectric relaxation type of HBCP has been determined as nearly‐Debye type because the absorption coefficient, α, equals to 0.01655. From the conductivity point of view, HBCP displays dc conductivity at the low and high frequency regions that correspond to 100 Hz–12 kHz and 3.3 MHz–15 MHz, respectively. On the other hand, it has been revealed that the ac conductivity of the LC system investigated obeys Super Linear Power Law (SLPL) at the intermediate frequency domain. Copyright © 2015 John Wiley & Sons, Ltd.     

Novel flame‐retardant thermosets: Diglycidyl ether of bisphenol A as a curing agent of boron‐containing phenolic resins

Boron‐containing novolac resins were synthesized by the modification of a commercial novolac resin with different contents of bis(benzo‐1,3,2‐dioxaborolanyl)oxide. These novolac resins were crosslinked with diglycidyl ether of bisphenol A (DGEBA), and their thermal, thermodynamomechanical, and flame‐retardant properties were evaluated. The boron‐containing novolac resins were less thermally stable than the unmodified novolac resin. Their modification degree and DGEBA content were related to the crosslinking density of the materials. The boron‐containing novolac resins generated boric acid at high temperatures and gave an intumescent char that slowed down the degradation and prevented it from being total. They also showed good flame‐retardant properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1701–1710, 2006