Highest Limiting Oxygen Index Value Research Articles

A novel flame retardant containing phosphorus, nitrogen, and sulfur

In this article, a novel intumescent flame retardant (IFR) PNSFR containing three flame-retardant elements, phosphorus, nitrogen, and sulfur was designed and synthesized. Then a series of flame-retardant thermoplastic polyurethanes (TPU) were prepared using the PNSFR. The effects of the flame retardant on the flammability of TPU/PNSFR composites were investigated by limited oxygen index (LOI) and UL-94 vertical burning. The results showed that TPU containing 10 mass% PNSFR had the highest LOI value (36) and could reach the V-0 rating. The flame-retardant mechanism of PNSFR in TPU was also disclosed using thermogravimetric analysis (TG), scanning electron micrograph, TG-infared spectrometry, and Fourier transform infrared spectroscopy. The sulfur and phosphorus elements of PNSFR can be kept in residual char. Moreover, an optimal loading amount of the IFR in TPU is in favor of forming dense and continuous char layer to prevent heat transfer and the spread of flammable gases. The IFR PNSFR may find potential use for various flame-retardant polyurethanes.

Synthesis of a novel flame retardant containing phosphorus-nitrogen and its comparison for cotton fabric

A new charring agent, a derivative of cyanuric chloride, mono-substituted, dimethyl (4,6-dichloro-1,3,5-triazin-2- yloxy)methylphosphonate (CN), was synthesized in good yield and characterized. Its flame retardant and thermogravimetric properties were compared to those of the di-substituted compound, tetramethyl (6-chloro-1,3,5-triazine-2,4-diyl)bis(oxy)bis (methylene)diphosphonate (CN-1), which was prepared in previous work. All untreated fabric showed limiting oxygen index (LOI) values of about 18 vol% oxygen in nitrogen. Fabrics treated with CN at 5-21 wt% add-ons had high LOI values of 30- 40 vol%, while fabrics treated with CN-1 at 5-19 wt% add-ons had low to high LOI value of 20-36 vol%. In 45 o angle flammability tests, all treated fabrics with CN and CN-1 were passed and some fabrics were not igniting at all. Thermal degradation revealed that onset of degradation and the char yield of CN compound is higher than that of CN-1. Treated fabric with CN, 21 wt% add-on, had an onset of degradation of 240 oC, while fabric treated with CN-1, 19 wt% add-on displayed an onset of degradation of 230 o C. Despite the differences in onset temperature, the two samples provided almost the same char yield at 600 o C, 35 and 36 %. With Fourier transform infrared (FTIR), samples of treated/unburned and treated/burned of CN and CN-1 showed the same functional groups and revealed the disappearance of triazine group and P-O-methyl after burning. Additionally, scanning electron microscopy (SEM) showed that both CN and CN-1 acted as flame retardants by the same mechanism and characterized the surface morphology of the flame retardant treated twill fabrics.

Novel Spirocyclic Phosphazene-Based Epoxy Resin for Halogen-Free Fire Resistance: Synthesis, Curing Behaviors, and Flammability Characteristics

A novel halogen-free fire resistant epoxy resin with pendent spiro-cyclotriphosphazene groups was designed and synthesized via a three-step synthetic pathway. The chemical structures and compositions of spiro-cyclotriphosphazene precursors and final product were confirmed by (1)H, (13)C, and (31)P NMR spectroscopy, mass spectroscopy, elemental analysis, and Fourier transform infrared spectroscopy. The thermal curing behaviors of the synthesized epoxy resin with 4,4'-diamino-diphenylmethane, 4,4'-diamino-diphenyl sulfone, and novolac as hardeners were investigated by differential scanning calorimetry (DSC), and the curing kinetics were also studied under a nonisothermal condition. The evaluation of the thermal properties demonstrated that these thermosets achieved a good thermal resistance due to their high glass transition temperatures more than 150 °C, and also gained high thermal stabilities with high char yields. The flammability characteristics of the spirocyclic phosphazene-based epoxy thermosets cured with these three hardeners were investigated on the basis of the results obtained from the limiting oxygen index (LOI) and UL-94 vertical burning experiments as well as the analysis of the residual chars collected from the vertical burning tests. The high LOI values and UL-94 V-0 classification of these epoxy thermosets indicated that the incorporation of phosphazene rings into the backbone chain imparts nonflammability to the epoxy resin owing to the unique combination of phosphorus and nitrogen following by a synergistic effect on flame retardancy. The epoxy resin obtained in this study is a green functional polymer and will become a potential candidate for fire- and heat-resistant applications in electronic and microelectronic fields with more safety and excellent performance.

Comparison of the effect of montmorillonite, magnesium hydroxide and a mixture of both on the flammability properties and mechanism of char formation of HDPE composites

The effects of pristine (MMT), organo-modified montmorillonite (OMMT), magnesium hydroxide (MDH) and combination of montmorillonites and magnesium hydroxide on the fire retardancy of high density polyethylene were assessed using TGA-FTIR analysis, limiting oxygen index (LOI), UL-94 test and the cone calorimeter. The results indicated that the addition of organo-modified montmorillonite to high density polyethylene HDPE/MDH composites allowed achievement of higher limiting oxygen index values at lower total flame retardants content while fulfilling the fire retardancy requirements. High density polyethylene composites with pristine (MMT) or organo-modified (OMMT) montmorillonite were prepared by melt-blending in a twin-screw co-rotating extruder introducing two methods. In the first method montmorillonites or magnesium hydroxide was directly provided to high density polyethylene matrix to obtain HDPE/MMT, HDPE/OMMT and HDPE/MDH composites. The second method consists of two stages. The extrusion of master batches of ethylene-vinyl acetate copolymer (EVA) with pristine or organo-modified montmorillonite (ratio 1:1) in first stage and dilution of obtained premix in high density polyethylene matrix in second stage. The thermogravimetry coupled with Fourier transform infrared spectroscopy (TGA-FTIR) results indicate that pristine MMT, OMMT, MDH and their combination have an effect on the thermal degradation of HDPE in oxidative atmosphere. Cone calorimetry showed that, montmorillonites shorten times of ignition and reduce peak heat release rates (peak HRRs). Magnesium hydroxide, however delayed ignition owing to loss of water at lower temperatures, reduced the peak HRR. The reduced peak HRRs for OMMT and MDH together can be attributed to the formation of a surface layer which acts as mass and heat barrier to protect the underlying material from further burning. The flame retardant efficiency of magnesium hydroxide in high density polyethylene matrix was improved by application of MMT or OMMT introduced in ethylene-vinyl acetate copolymer.

New routes to flame retard polyamide 6,6 for electrical applications

Polyamide 6,6 is used in many industrial fields such as housing materials, transport or electrical engineering applications. Due to its chemical composition, this polymer is easily flammable. As far as the main applications concern electrical and electronic equipments, its flame-retardant properties become an important requirement. The most discriminating tests are the limiting oxygen index, UL94 and glow wire flammability index. The aim is to obtain high limiting oxygen index values, V0 rating at UL94 test for 1.6- or 0.8-mm-thick samples and a validation at 960°C of the glow wire flammability index. The usual way to fire retard polyamide 6,6 consists of incorporating an important loading of fire-retardant additives, which often reduce the intrinsic properties of the polymer. It is also difficult to combine a thin polymer thickness (e.g. 0.8 mm) and a high amount of additives because of processing issues. In this article, we first carried out a rapid screening to determine the best fire retardant for polyamide 6,6 and its optimized amount to achieve the previously defined fire retardant properties. It was shown that an amount of 23% of aluminium diethylphosphinate Exolit OP1230 allows reaching the requirements. Then, carrying out two different surface treatments (coating of polysiloxanes by plasma-enhanced chemical vapour deposition and use of an intumescent waterborne varnish), we have tried to reach the same results. It was shown that the use of surface treatment alone does not allow reaching the objectives. As a consequence, the combination of the bulk approach at low loadings with the surface treatment was investigated. This new route allows the combination of the condensed phase mechanism of the intumescent barrier with the gas phase mechanism of the OP1230 and leads to very good results: the use of 5% of the flame-retardant additives combined with a 100-µm-thick waterborne intumescent varnish leads to better results than a 23% of additive loading.

The effect of different organic modified montmorillonites (OMMTs) on the thermal properties and flammability of PLA/MCAPP/lignin systems

AbstractThe effect of different organic modified montmorillonites (DK1, DK2, and DK4) based on a novel intumescent flame retardant (IFR) poly(lactic acid) (PLA) system is reported. The IFR system was composed of microencapsulated ammonium polyphosphate and lignin. The morphological characterization of PLA/OMMT nanocomposites was conducted by X‐ray diffractometry and transmission electron microscopy. The flame retardant and thermal properties of the composites were evaluated by limiting oxygen index (LOI), vertical burning test (UL‐94), and cone calorimeter. From the results, it could be seen that the sample containing DK2 possessed the best flame retardance, such as lower peak heat release rate (pHRR) and higher LOI value. The thermal degradation and gas products of the samples were monitored by thermogravimetric analysis and thermogravimetric analysis infrared spectrometry. Scanning electron microscopy was used to explore the surface morphology of the char residues. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013

Burning behavior and thermal degradation kinetics of surface photografted polyamide 6.6 fabric

Surface photografting with 2‐hydroxyethyl methacrylate phosphate has been used to improve the flame retardancy of polyamide 6.6 fabrics. Limiting oxygen index tests and vertical burning tests were used to characterize the fire performance. The highest limiting oxygen index value of the grafted sample can reach up to 31.2, which is 58% higher than that of the ungrafted fabric. The thermal stability and char morphology of the polyamide 6.6 fabrics have been characterized by the thermogravimetric analysis and scanning electron microscopy analysis. Kinetic analysis on fabric samples was investigated, and the results show that the activation energy of the grafted sample is higher than that of the ungrafted fabric. Copyright © 2012 John Wiley & Sons, Ltd.

The Effects of Vinyl Acetate and Polyoxyethylene on the Properties of Halogen-Free Flame Retardant EVA Composites

The effect of vinyl acetate (VA) content on the Properties of Intumescent flame retardant ethylene-vinyl acetate copolymer (IFR EVA) material was studied. Ammonium polyphosphate and pentaerythritol (APP/PER) was used to prepare the IFR EVA materials. The burning behavior, thermal stabilization, and mechanical properties of the IFR EVAs composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, and tensile measurements. The content of VA had a large influence on the flame retardancy. The curves of V 1max (the first maximal weight loss rate) and LOI values with respect to the VA values had the same trends. The larger the V 1max value was, the more significant the thermal degradation of the acetate functions. The IFR EVA composites (with 10 wt% VA content) had the highest LOI value with the lowest residual weight. This indicated that the decomposition rate, char-forming rate of the IFR materials had an influence on the flame retardancy of these materials. A good and coherent charred productive layer on VA10 might be produced. The elongation at break of the EVA18 (with the VA content of 18 wt%)/APP/PER IFR system, containing 35 wt% APP/PER, was improved by the incorporation of octene-ethylene copolymer (POE), but the addition of POE decreased the tensile strength of these composites. The initial decomposition temperature for these composites with 5 wt% decomposition (T –0.5 wt%) and residual weight at 800 °C of these composites decreased as the POE content increased. However, all the IFR EVA18 composites containing 35 wt% APP/PER and various contents of POE (from 0 to 20 wt%) could pass the UL V-0 rating and had high LOI values, about 41 vol%. The POE content had little effect on the flame retardancy of the EVA18/APP/PER composites.

Synthesis, characterization and curing properties of a novel cyclolinear phosphazene-based epoxy resin for halogen-free flame retardancy and high performance

A novel cyclolinear phosphazene-based epoxy resin has been synthesized through a four-step synthetic route. The curing behaviors of this epoxy resin with methyl tetrahydrophthalic anhydride, 4,4′-diaminodiphenylmethane, and novolak as hardeners were investigated by differential scanning calorimetry (DSC). The thermal behaviors and stabilities were also evaluated with DSC and thermogravimetric analysis. These thermosets achieved high glass transition temperatures over 150 °C and also gained good thermal stabilities with high char yields. The flammability characteristics of the cyclolinear phosphazene-based epoxy thermosets were investigated by limiting oxygen index (LOI) and UL-94 vertical burning experiments. The high LOI values and UL-94 V-0 classification of these epoxy thermosets indicate that the incorporation of phosphazene rings into the molecular backbone imparts non-flammability to the epoxy resin as a result of the unique combination of phosphorus and nitrogen following by a synergistic effect on flame retardancy. The analysis of the residual chars collected from the UL-94 test demonstrates that cyclotriphosphazene moieties of this epoxy resin can enhance char formation during combustion serving as a barrier against heat and oxygen diffusion, and consequently the flame retardancy of the thermosets is improved significantly.

Preparation and flame retardancy of a novel flame‐retardant poly(ethylene‐co‐vinyl acetate)/aluminum hydroxide composites containing phosphorus

AbstractA novel flame‐retardant (SPDH) containing phosphorus was synthesized through the reaction of 10‐(2,5‐dihydroxyphenyl)‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and synthesized intermediate product 3,9‐dichloro‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro[5.5] undecane‐3,9‐dioxide, which was used for optimizing the flame retardancy of ethylene‐vinyl acetate copolymer (EVM) rubber/aluminum hydroxide (ATH) composites. The microstructure of SPDH was characterized and determined by Fourier transform infrared and nuclear magnetic resonance spectroscopy. Thermogravimetric analysis (TGA) showed that SPDH had good charring effect at high temperature (600°C). The flame retardancy of the optimized EVM/ATH composites by SPDH was investigated by limiting oxygen index (LOI), cone calorimeter, and UL‐94 vertical burning tests. A higher LOI value (29.8%) and better UL‐94 rating (V‐0) can be achieved for the optimized EVM/ATH composite (EVM‐7) than EVM/ATH composite without SPDH (EVM‐3) with the total loading of additives. The heat release rate decreased and residual mass increased gradually as the loading of SPDH increased for the optimized EVM/ATH composites. There existed distinct synergistic flame‐retardant effect between SPDH and ATH in EVM matrix. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Effect of Cellulose Acetate Butyrate Microencapsulated Ammonium Polyphosphate on the Flame Retardancy, Mechanical, Electrical, and Thermal Properties of Intumescent Flame-Retardant Ethylene–Vinyl Acetate Copolymer/Microencapsulated Ammonium Polyphosphate/Polyamide-6 Blends

Ammonium polyphosphate (APP), a widely used intumescent flame retardant, has been microencapsulated by cellulose acetate butyrate with the aim of enhancing the water resistance of APP and the compatibility between the ethylene-vinyl acetate copolymer (EVA) matrix and APP. The structure of microencapsulated ammonium polyphosphate (MCAPP) was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and water contact angle (WCA). The flame retadancy and thermal stability were investigated by a limiting oxygen index (LOI) test, UL-94 test, cone calorimeter, and thermogravimetric analysis (TGA). The WCA results indicated that MCAPP has excellent water resistance and hydrophobicity. The results demonstrated that MCAPP enhanced interfacial adhesion, mechanical, electrical, and thermal stability of the EVA/MCAPP/polyamide-6 (PA-6) system. The microencapsulation not only imparted EVA/MCAPP/PA-6 with a higher LOI value and UL-94 rating but also could significantly improve the fire safety. Furthermore, the microencapsulated EVA/MCAPP/PA-6 composites can still pass the UL-94 V-0 rating after treatment with water for 3 days at 70 °C, indicating excellent water resistance. This investigation provides a promising formulation for the intumescent flame retardant EVA with excellent properties.

Synthesis and characterization of P/Si flame retardant and its application in epoxy systems

In this report, a novel phosphorus/silicon‐containing reactive flame retardant, hexa(3‐triglycidyloxysilylpropyl)triphosphazene (HGPP), was synthesized and characterized by Fourier transform infrared spectrometry and nuclear magnetic resonance spectra (1H, 31P, and 29Si), respectively. To prepare cured epoxy, HGPP had been co‐cured with diglycidyl ether of bisphenol‐A (DGEBA) via 4,4‐diaminodiphenylsulfone as a curing agent. The mechanical, thermal, and flame retardant properties of the cured epoxy were evaluated by dynamic mechanical analysis, thermogravimetric analysis, and limiting oxygen index (LOI). According to these results, it could be found that incorporation of HGPP in the cured epoxy system showed good thermal stability, high LOI values, and high char yield at high temperature. As moderate loading of HGPP in the epoxy system, its storage modulus and glass transition temperature were higher than those of neat DGEBA. Copyright © 2011 John Wiley & Sons, Ltd.

Comparative study on flame retardancy and thermal degradation of phosphorus- and silicon-containing epoxy resin composites

Epoxy composites containing phosphorus and/or silicon were prepared using polyphenylmethoxysilicone (PPMS) and microencapsulated ammonium polyphosphate (MFAPP) as modifiers. Siliconized epoxy copolymer (EPMS) was obtained via the polycondensation of PPMS and diglycidyl ethers of bisphenol A (DGEBA) type epoxy resin. Then MFAPP was added into EPMS or DGEBA based hybrids respectively to improve their flame retardancy further. Thermal and flame retardant properties of EPMS/MFAPP and DGEBA/MFAPP composites were evaluated by Limited Oxygen index (LOI), UL-94 test and thermogravimetric analysis (TGA). The higher LOI value and UL-94 rating confirmed that MFAPP was an effective flame retardant in DGEBA compared with EPMS. A remarkable synergistic effect of phosphorus and silicon on flame retardation of EPMS/MFAPP was not observed. The reason was that the flame retardancy of epoxy composites containing phosphorus was based on solid phase. FTIR spectra of the char residue showed that when MFAPP was added, without sufficient O-H groups in EPMS/MFAPP, an effective insulative layer which protects underlying materials can’t form during combustion.

Study on the flame retardancy of EVM/magnesium hydroxide composites optimized with a flame retardant containing phosphorus and silicon

A novel phosphorus-silicon-containing flame retardant, spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride/9, 10-dihydro-9-oxa-10-phosphaphanthrene-10-oxide/vinyl methyl dimethoxysilane (SPDV), was synthesized successfully and used for optimizing the flame retardancy of ethylene-vinyl acetate copolymer (EVM) rubber/magnesium hydroxide (MDH) composites. The microstructure of SPDV was characterized and determined by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. Thermogravimetric analysis (TGA) showed that SPDV had good charring effect in air even at high temperature (800°C). The flame retardancy of the optimized EVM/MDH composites by SPDV was investigated by limiting oxygen index (LOI), cone calorimeter, and UL-94 vertical burning tests. A higher LOI value (29.4%) and better UL-94 rating (V-0) can be achieved for the optimized EVM/MDH composite (EVM-7) than EVM/MDH composite without SPDV (EVM-3) with the total loading of additives. The HRR decreased and residual mass increased gradually as the loading of SPDV increased for the optimized EVM/MDH composites. There existed distinct synergistic intumescent flame-retardant effect between SPDV and MDH in EVM matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Acoustical and fire-retardant properties of jute composite materials

This research aims to study the acoustical and flammability properties of biodegradable and easily disposable natural fibre jute and its composite for noise reduction in house hold appliances, automotive and architectural applications. Acoustical properties of jute fibre and felt (natural rubber latex jute composite) were measured in terms of normal specific sound absorption coefficient and sound transmission loss whereas fire retardant tests included limiting oxygen, flame propagation and smoke density test. The results illustrate that low density jute is a better sound absorber as compared to high density jute material, moreover natural rubber latex jute composite gives higher sound transmission class value than jute felt/cloth. Results were also compared with commercially available synthetic, non-biodegradable, glass fibre which indicates that the noise reduction coefficient value and sound transmission class rating of natural rubber latex jute felt are comparable to that of the popular fibre glass. Fire retardant tests show composite’s high limiting oxygen index value as compared to fibreboard and other natural sound absorbing material, wool, low smoke density rating and low light absorption with respect to fibre glass as well as self fire extinguishing ability.

A effective flame retardant for epoxy resins based on poly(DOPO substituted dihydroxyl phenyl pentaerythritol diphosphonate)

Poly(DOPO substituted dihydroxyl phenyl pentaerythritol diphosphonate) (PFR) was synthesized via the reaction between 10-(2,5-dihydroxyl-phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-BQ) and pentaerythritol diphosphonate dichloride (SPDPC). The structures of PFR were characterized by Fourier transformed infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance ( 1H NMR). Thermal degradation behaviors and flame retardant properties of the epoxy resin (ER)/PFR systems were investigated from the thermogravimetric analysis (TGA), UL-94 test and the limiting oxygen index (LOI) test. Moreover, the surface morphology of the char residue was studied by scanning electron microscopy (SEM). When the PFR content reached 10 wt%, the epoxy resin system met the UL-94 V0 classification and the LOI value of 30.2. The microscale combustion calorimetry (MCC) was used to evaluate the combustion behaviors of the ER/PFR. It was found that the addition of PFR obviously decreased the value of peak heat release rate and total heat release of the hybrids. The TGA results showed that the epoxy resin with 10 wt% PFR exhibited high char yields. The high char yields and the high limiting oxygen index values were found to certify the excellent flame retardancy of this phosphorus-containing epoxy resin.

Synthesis and Application in Polypropylene of a Novel of Phosphorus-Containing Intumescent Flame Retardant

A novel phosphorus-containing triazine oligomer poly(2-morpholinyl-4-penta-erythritol phosphate-1,3,5-triazine) (PMPT) was synthesized as a kind of tri-component intumescent flame retardant (IFR). The chemical structure of PMPT was characterized by FTIR, 1H-NMR and 31P-NMR, and the mechanical and flammability properties of FR-PP were measured. The FTIR results showed that the expected chemical reactions had happened at each step. The 1H-NMR and 31P-NMR spectra also agreed with the chemical structure of PMPT. The slight effect of PMPT on the mechanical properties of FR-PP suggested that PMPT and PP are compatible. The high limited oxygen index (LOI) values of FR-PP revealed that PMPT was an efficient IFR and there was the synergistic effect between PMPT and ammonium polyphosphate/ pentaerythritol (APP/PER).

Synergistic Flame-Retarded Effect of Synthetic Dawsonite on an EVA/Magnesium Hydroxide System

A novel halogen-free flame-retardant system composed of dawsonite and magnesium hydroxide was used for flame-retarded ethylene vinyl acetate. The thermal and fire properties of flame-retarded ethylene vinyl acetate system were evaluated by thermagravimetric analysis (TGA), limiting oxygen index (LOI) and UL-94 test while the structure of combustion residue was characterized by scanning electron microscopy (SEM). The highest LOI value and the V-0 grade of the composites were attained by the 5 wt% incorporation of dawsonite. These advancements are ascribed to the char stabilizer effect of fibrous-like combustion residue of dawsonite leading to increased strength of the residue.

Thermally stable and flame retardant low dielectric polymers based on cyclotriphosphazenes

We prepared thermally stable, low dielectric polymers by thermal polymerization of cyclotriphosphazenes bearing acetylene or styrene groups. Homosubstituted cyclotriphosphazene 1, containing acetylene groups, was synthesized by reaction of hexachlorocyclotriphosphazene with sodium salts of 4′-trimethylsilylethynyl-1,1′-biphenyl-4-ol and subsequent removal of trimethylsilyl groups under basic conditions. Heterosubstituted cyclotriphosphazene 2 was prepared using 4-phenylphenol as a cosubstituent. Cyclotriphosphazene 3 with styrene groups was prepared by reaction of hexachlorocyclotriphosphazene with sodium salts of 4-hydroxystyrene. Highly cross-linked polymers were obtained by thermal polymerization of the cyclotriphosphazenes at 200 °C for 1 and 2 and at 150 °C for 3. The 5% weight loss temperatures of the cross-linked polymers of compounds 1–3, measured by TGA, were above 470 °C. The flame-retardant property of the polymers was evaluated by measuring LOI (limiting oxygen index) values. The polymers of cyclotriphosphazenes 1–3 showed very high LOI values of 52, 50 and 49, respectively. We also prepared copolymers of cyclotriphosphazene 3 with styrene by UV irradiation in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone). In the TGA thermograms, the copolymers showed good thermal stability, nearly comparable to the homopolymer of 3 when the composition of 3 was higher than 60%. The dielectric properties of the polymers were measured by a metal–insulator–metal method. The polymer obtained from acetylene-containing cyclotriphosphazene 1 showed dielectric constant and dielectric loss values of about 3.12 and 0.0016, respectively, at 1 GHz. The polymer of cyclotriphosphazene 3 showed a dielectric constant of 2.4 and a dielectric loss of 0.0014 at 1 GHz.

Development of flame retardant phosphorus- and silicon-containing polybenzoxazines

The copolymerisation of benzoxazine of bisphenol A and diglycidyl ether of (2,5-dihydroxyphenyl)diphenyl phosphine oxide or diglycidyloxymethylphenylsilane has been studied. In all samples the molar ratio of the benzoxazine–epoxy system was varied to achieve different phosphorus or silicon contents. Their thermal, dynamic-mechanical and flame retardant properties were evaluated. The high limiting oxygen index values confirmed that the phosphorus-containing benzoxazine–epoxy resins are effective flame retardants, but no efficiency of silicon on flame retardation was observed.