Recent developments in the chemistry of halogen-free flame retardant polymers

Phosphorus-containing polymers synthesised via nitroxide-mediated polymerisation and their grafting on chitosan by grafting to and grafting from approaches

The phosphorus-based methacrylate monomers (h)MAPC1 have been polymerized by NMP and grafted on chitosan.

Intrinsic flame retardant phosphonate-based vitrimers as a recyclable alternative for commodity polymers in composite materials

Vitrimers are a promising alternative to conventional composite materials as they can be recycled and reshaped but still need additives. Herein, intrinsic flame-retardant phosphorus-containing vitrimers are presented, which were used in composites.

Practical Synthesis of Phosphinic Amides/Phosphoramidates through Catalytic Oxidative Coupling of Amines and P(O)-H Compounds

Herein, we report a highly efficient ZnI₂ -triggered oxidative cross-coupling reaction of P(O)-H compounds and amines. This operationally simple protocol provides unprecedented generic access to phosphinic amides/phosphoramidate derivatives in good yields and short reaction time. Besides, the reaction proceeds under mild conditions, which avoids the use of hazardous reagents, and is applicable to scale-up syntheses as well as late-stage functionalization of drug molecules. The stereospecific coupling is also achieved from readily available optically enriched P(O)-H compounds.

Improved thermally stable oligoetherols from 6-aminouracil, ethylene carbonate and boric acid

Syntheses of oligoetherols with a 1,3-pyrimidine ring and boron atoms using 6-aminouracil, ethylene carbonate and boric acid has been proposed. The structure of the obtained products were determined by instrumental methods (IR, 1H-NMR and MALDI-ToF spectra). The physicochemical and thermal properties of oligoetherols were examined. The products were characterized by high thermal stability. Based on the tests performed, it was found that oligoetherols obtained from 6-aminouracil, boric acid and ethylene carbonate are suitable for the manufacturing of polyurethane foams with improved thermal stability and reduced flammability.

One-Step Synthesis of Highly Efficient Oligo(phenylphosphonic Dihydroxypropyl Silicone Oil) Flame Retardant for Polycarbonate

A highly efficient flame retardant and smoke suppression oligomer, oligo(phenylphosphonic dihydroxypropyl silicone oil) (PPSO), was synthesized by a one-step reaction. The chemical structure of PPSO was confirmed by Fourier transform infrared (FTIR), ³¹P nuclear magnetic resonance (³¹P NMR), and ²⁹Si nuclear magnetic resonance (²⁹Si NMR). The flame-retardant effect of PPSO on the polycarbonate (PC) matrix was investigated by limiting oxygen index, UL-94 vertical burning test, and cone calorimetry, respectively. The results showed that PC/PPSO composites passed UL-94 V-0 rate testing with only 1.3 wt. % PPSO. Furthermore, the incorporation of PPSO can suppress the release of smoke. The flame-retardant mechanism was also investigated via thermogravimetric analysis-fourier transform infrared spectroscopy (TG-FTIR), field-emission scanning electronic microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. From the result of pyrolysis gas and char residue, PPSO played a synergistic flame-retardant mechanism including the gas phase and the condensed phase.

Synthesis of Bisphenol A Based Phosphazene-Containing Epoxy Resin with Reduced Viscosity

Phosphazene-containing epoxy oligomers (PEO) were synthesized by the interaction of hexachlorocyclotriphosphazene (HCP), phenol, and bisphenol A in a medium of excess of epichlorohydrin using potassium carbonate and hydroxide as HCl acceptors with the aim of obtaining a product with lower viscosity and higher phosphazene content. PEOs are mixtures of epoxycyclophosphazene (ECP) and a conventional organic epoxy resin based on bisphenol A in an amount controlled by the ratio of the initial mono- and diphenol. According to ³¹P NMR spectroscopy, pentasubstituted aryloxycyclotrophosphazene compounds predominate in the ECP composition. The relative content in the ECP radicals of mono- and diphenol was determined by the MALDI-TOF mass spectrometry method. The organic epoxy fraction, according to gas chromatograpy-mass spectrometry (GC-MS), contains 50-70 wt % diglycidyl ether of bisphenol A. PEO resins obtained in the present work have reduced viscosity when compared to other known phosphazene-containging epoxy resins while phosphazene content is still about 50 wt %. Resins with an epoxy number within 12-17 wt %, are cured by conventional curing agents to form compositions with flame-retardant properties, while other characteristics of these compositions are at the level of conventional epoxy materials.

Aromatic vs. Aliphatic Hyperbranched Polyphosphoesters as Flame Retardants in Epoxy Resins

The current trend for future flame retardants (FRs) goes to novel efficient halogen-free materials, due to the ban of several halogenated FRs. Among the most promising alternatives are phosphorus-based FRs, and of those, polymeric materials with complex shape have been recently reported. Herein, we present novel halogen-free aromatic and aliphatic hyperbranched polyphosphoesters (hbPPEs), which were synthesized by olefin metathesis polymerization and investigated them as a FR in epoxy resins. We compare their efficiency (aliphatic vs. aromatic) and further assess the differences between the monomeric compounds and the hbPPEs. The decomposition and vaporizing behavior of a compound is an important factor in its flame-retardant behavior, but also the interaction with the pyrolyzing matrix has a significant influence on the performance. Therefore, the challenge in designing a FR is to optimize the chemical structure and its decomposition pathway to the matrix, with regards to time and temperature. This behavior becomes obvious in this study, and explains the superior gas phase activity of the aliphatic FRs.

Novel Nitrogen-Phosphorus Flame Retardant Based on Phosphonamidate: Thermal Stability and Flame Retardancy

A novel nitrogen-phosphorus flame retardant (P-N FR) based on phosphonamidate, dimethyl N,N'-1,3-phenylenebis(P-methylphosphonamidate) (DMPMP), was successfully synthesized and its flame-retarding performances and thermal degradation were compared with those of other P-N FRs and a phosphorus-based FR such as resorcinol bis(diphenyl phosphate) (RDP). DMPMP was applied to acrylonitrile-butadiene-styrene (ABS) and ethylene-vinyl acetate (EVA) to investigate the factors governing the flame-retarding behaviors of P-N FRs which would make them efficient for noncharrable polymers. V-0 ratings were achieved at 20 wt % loading of DMPMP for ABS and at a much lesser amount of DMPMP loading (10 wt %) for EVA. Meanwhile, no rating and V-2 were achieved even at 20-30 wt % loading of other P-N FRs or RDP for ABS and EVA, respectively. The results from thermogravimetric analysis, Fourier transform infrared, and UL-94V indicated that DMPMP is a highly efficient FR and acts mainly in a gas-phase flame-retarding mode of action. The condensed phase of DMPMP also contributed to the flame retardancy property through -NH- groups which tendentiously generate a nitrogen-phosphorus-rich residue because of the intermolecular coupling transesterification reaction. These results demonstrated the assumption that DMPMP has a high P content and good hydrostability, which exhibits good flame retardancy for noncharrable polymers such as ABS and EVA.

Functionalized Cellulose Nanocrystals: A Potential Fire Retardant for Polymer Composites

The flammability of synthetic thermoplastic polymers has been recognized as an increasingly important safety problem. The goal of this study was to evaluate a green and safe fire-retardant system comprising of cellulose nanocrystals (CNC) and zinc oxide nanoparticles (ZnO). CNCs coated with nano ZnO were incorporated in the high-density polyethylene polymer (HDPE) matrix at different concentrations. Fire testing results of different formulations of HDPE containing 0.4 to 1.0% zinc oxide coated CNC exhibited a substantial decrease in the average mass loss, peak heat release rate and total smoke release. The time to ignition exhibited a positive correlation with CNC-ZnO concentration. Modest improvement in the flexural strength and moduli of composites was noticed validating no adverse effects of CNC-ZnO complex. The transmission electron microscopy further confirmed dispersion of nanoparticles as well as the presence of some nanoparticle aggregates in the matrix. The uniform dispersion of CNC-ZnO complex is expected to further improve fire and mechanical properties of polymer.

Transition metal-free phosphonocarboxylation of alkenes with carbon dioxide via visible-light photoredox catalysis

Catalytic difunctionalization of alkenes has been an ideal strategy to generate structurally complex molecules with diverse substitution patterns. Although both phosphonyl and carboxyl groups are valuable functional groups, the simultaneous incorporation of them via catalytic difunctionalization of alkenes, ideally from abundant, inexpensive and easy-to-handle raw materials, has not been realized. Herein, we report the phosphonocarboxylation of alkenes with CO2 via visible-light photoredox catalysis. This strategy is sustainable, general and practical, providing facile access to important β-phosphono carboxylic acids, including structurally complex unnatural α-amino acids. Diverse alkenes, including enamides, styrenes, enolsilanes and acrylates, undergo such reactions efficiently under mild reaction conditions. Moreover, this method represents a rare example of redox-neutral difunctionalization of alkenes with H-P(O) compounds, including diaryl- and dialkyl- phosphine oxides and phosphites. Importantly, these transition-metal-free reactions also feature low catalyst loading, high regio- and chemo-selectivities, good functional group tolerance, easy scalability and potential for product derivatization.

Improving the Flame Retardance of Polyisocyanurate Foams by Dibenzo[d,f][1,3,2]dioxaphosphepine 6-Oxide-Containing Additives

A series of new flame retardants (FR) based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) incorporating acrylates and benzoquinone were developed previously. In this study, we examine the fire behavior of the new flame retardants in polyisocyanurate (PIR) foams. The foam characteristics, thermal decomposition, and fire behavior are investigated. The fire properties of the foams containing BPPO-based derivatives were found to depend on the chemical structure of the substituents. We also compare our results to state-of-the-art non-halogenated FR such as triphenylphosphate and chemically similar phosphinate, i.e. 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO), based derivatives to discuss the role of the phosphorus oxidation state.

Curing of Epoxy Resin DER-331 by Hexakis(4-acetamidophenoxy)cyclotriphosphazene and Properties of the Prepared Composition

The method of optical wedge revealed that the optimum temperature for compatibility of hexakis(4-acetamidophenoxy)cyclotriphosphazene (ACP) and DER-331 epoxy resin is in the range of 220-260 °C. The interdiffusion time of components at these temperatures is about 30 min. The TGA and differential scanning calorimetry (DSC) methods revealed the curing temperature of 280 °С for this composition. IR spectroscopy confirmed that the reaction between the resin and ACP is completed within 10 min. According to the DSC data, a glass transition temperature of 130 °С was estimated for the cured resin. Combustion test UL-94 demonstrated that the obtained material can be assigned to the fireproof category of V-0. Burning droplets were not formed during the burning. The coke formed during the combustion of samples possessed a dense and porous structure. The shape of pores is closed, while their size is in the range of 0.2-200 µm.

Interface decoration of exfoliated MXene ultra-thin nanosheets for fire and smoke suppressions of thermoplastic polyurethane elastomer

Thermoplastic polyurethane (TPU) has broad applications as lightweight materials due to its multiple advantages and unique properties. Nevertheless, toxicity emission under fire conditions remains a major concern, particularly in building fire scenarios. To circumvent the problem, it is imperative that an effective flame retardant is sought to suppress the flame and release of combustion/smoke products whilst maintaining the favorable material properties of TPU. In the current work, a simple method is proposed for the preparation and utilization of cetyltrimethyl ammonium bromide (CTAB) and tetrabutyl phosphine chloride (TBPC) modified Ti₃C₂ (MXene) ultra-thin nanosheets. During the cone calorimeter tests, significant reduction in peak heat release rate (51.2% and 52.2%), peak smoke production rate (57.1% and 57.4%), peak CO production (39.4% and 41.6%) and peak CO₂ production (49.7% and 51.7%) were recorded by the mere introduction of 2 wt.% CTAB-Ti₃C₂ and TBPC-Ti₃C₂ to TPU. These superior fire safety properties resulting from the significant reduction of the fire, smoke and toxicity hazards are attributed to the excellent dispersion, catalytic and barrier effect of Ti₃C₂ ultra-thin nanosheets in TPU. Future applications of exfoliated MXene nanosheets as flame retardant appear to be very promising.

Chain Extension and Synergistic Flame-Retardant Effect of Aromatic Schiff Base Diepoxide on Polyamide 6/Aluminum Diethylphosphinate Composites

A way to suppress the deterioration in mechanical properties of polyamide 6 (PA6) is required, especially with high loading of flame retardants in the matrix. In this study, a novel aromatic Schiff base diepoxide (DES) was synthesized. It exhibited an efficient chain extension effect on PA6 and a synergistic flame-retardant effect with aluminum diethylphosphinate (AlPi) for PA6. The PA6 composite with 16 wt.% AlPi only passed UL-94 V-0 rating at 1.6 mm thickness, while the combination of 1.5 wt.% DES with 13 wt.% AlPi induced PA6 to achieve a UL-94 V-0 rating at 0.8 mm thickness. The tensile, flexural, and Izod notched impact strengths were increased by 16.2%, 16.5%, and 24.9%, respectively, compared with those of V-0 flame-retarded PA6 composites with 16 wt.% AlPi. The flame-retarded mechanism of PA6/AlPi/DES was investigated by cone calorimetry and infrared characterization of the char residues and pyrolysis products. These results showed that DES had a synergistic effect with AlPi in condensed-phase flame retardation by promoting the production of aluminum phosphorus oxides and polyphosphates in the char residues.

Design and Application of Highly Efficient Flame Retardants for Polycarbonate Combining the Advantages of Cyclotriphosphazene and Silicone Oil

A novel flame retardant (HSPCTP) was successfully designed and incorporated into a polycarbonate (PC) matrix. Combining the advantages of cyclotriphosphazene and silicone oil, PC/HSPCTP composites passed UL-94 V-0 rating testing with only 3 wt% HSPCTP, and their LOI value increased from 25.0% to 28.4%. The findings showed that HSPCTP exhibits both gas-phase and solid-phase flame-retardant effects. Furthermore, the incorporation of HSPCTP into PC could suppress the release of smoke. Finally, the flame-retardant mechanism is discussed in depth.

Phosphine Oxide Containing Poly(pyridinium salt)s as Fire Retardant Materials

Six new rugged, high-temperature tolerant phosphine oxide-containing poly(4,4′-(p-phenylene)-bis(2,6-diphenylpyridinium)) polymers P-1, P-2, P-3, P-4, P-5, and P-6 are synthesized, characterized, and evaluated. Synthesis results in high yield and purity, as confirmed by elemental, proton (¹H), and carbon 13 (¹³C) nuclear magnetic resonance (NMR) spectra analyses. High glass transition temperatures (T_g > 230 °C) and high char yields (>50% at 700 °C) are determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. These new ionic polymers exhibit excellent processability, thin-film forming, high-temperature resistance, fire-resistance and retardation, coating, adhesion, mechanical and tensile strength, and n-type (electron transport) properties. The incorporation of phosphine oxide and bis(phenylpyridinium) moieties in the polymer backbones leads to high glass transition temperatures and excellent fire retardant properties, as determined by microcalorimetry measurements. The use of organic counterions allows these ionic polymers to be easily processable from several common organic solvents. A large variety of these polymers can be synthesized by utilizing structural variants of the bispyrylium salt, phosphine oxide containing diamine, and the counterion in a combinatorial fashion. These results make them very attractive for a number of applications, including as coating and structural component materials for automobiles, aircrafts, power and propulsion systems, firefighter garments, printed circuit boards, cabinets and housings for electronic and electrical components, construction materials, mattresses, carpets, upholstery and furniture, and paper-thin coatings for protecting important paper documents.

A Review of a Class of Emerging Contaminants: The Classification, Distribution, Intensity of Consumption, Synthesis Routes, Environmental Effects and Expectation of Pollution Abatement to Organophosphate Flame Retardants (OPFRs)

Organophosphate flame retardants (OPFRs) have been detected in various environmental matrices and have been identified as emerging contaminants (EC). Given the adverse influence of OPFRs, many researchers have focused on the absorption, bioaccumulation, metabolism, and internal exposure processes of OPFRs in animals and humans. This paper first reviews the evolution of various types of flame retardants (FRs) and the environmental pollution of OPFRs, the different absorption pathways of OPFRs by animals and humans (such as inhalation, ingestion, skin absorption and absorption), and then summarizes the environmental impacts of OPFRs, including their biological toxicity, bioaccumulation, persistence, migration, endocrine disruption and carcinogenicity. Based on limited available data and results, this study also summarizes the bioaccumulation and biomagnification potential of OPFRs in different types of biological and food nets. In addition, a new governance idea for the replacement of existing OPFRs from the source is proposed, seeking environmentally friendly alternatives to OPFRs in order to provide new ideas and theoretical guidance for the removal of OPFRs.

Preparation, characterization and flame retardancy of phosphorus-containing poly-styrene-acrylate emulsion

Phosphorus (P)-containing monomer (P-monomer) was firstly prepared by condensation reaction between 2-hydroxyethyl methacrylate and phosphorus pentoxide (P₂O₅) and then used to prepare P-containing poly-styrene-acrylate (P-PSA) emulsion by semi-continuous emulsion polymerization. The components of the prepared P-monomer were characterized by potentiometric titration method. The chemical composition of the P-PSA co-polymer was studied by Fourier-transform infrared spectra. The storage stability properties of P-PSA emulsion were tested by Ca²⁺, centrifugal and mechanical stability tests. The thermal stability and flame retardancy of the P-PSA co-polymer were studied by thermogravimetric analysis, limiting oxygen index and UL-94 method. The results show that stable P-PSA emulsions can be successfully prepared, and the latex particles present a spherical structure. When the P-monomer content is 30 wt%, the P-PSA co-polymer can pass the UL-94 test (V0 level) and the char yield is 54 wt% at 700°C. Scanning electron microscopy results indicate that incorporation of the P-monomer shows a condensed-phase flame-retardant effect. This study provides useful suggestions for the application of the flame-retardant P-PSA emulsion in the coating industry.

Functionalization of MXene Nanosheets for Polystyrene towards High Thermal Stability and Flame Retardant Properties

Fabricating high-performance MXene-based polymer nanocomposites is a huge challenge because of the poor dispersion and interfacial interaction of MXene nanosheets in the polymer matrix. To address the issue, MXene nanosheets were successfully exfoliated and subsequently modified by long-chain cationic agents with different chain lengths, i.e., decyltrimethylammonium bromide (DTAB), octadecyltrimethylammonium bromide (OTAB), and dihexadecyldimethylammonium bromide (DDAB). With the long-chain groups on their surface, modified Ti3C2 (MXene) nanosheets were well dispersed in N,N-dimethylformamide (DMF), resulting in the formation of uniform dispersion and strong interfacial adhesion within a polystyrene (PS) matrix. The thermal stability properties of cationic modified Ti3C2/PS nanocomposites were improved considerably with the temperatures at 5% weight loss increasing by 20 °C for DTAB-Ti3C2/PS, 25 °C for OTAB-Ti3C2/PS and 23 °C for DDAB-Ti3C2/PS, respectively. The modified MXene nanosheets also enhanced the flame-retardant properties of PS. Compared to neat PS, the peak heat release rate (PHRR) was reduced by approximately 26.4%, 21.5% and 20.8% for PS/OTAB-Ti3C2, PS/DDAB-Ti3C2 and PS/DTAB-Ti3C2, respectively. Significant reductions in CO and CO2 productions were also obtained in the cone calorimeter test and generally lower pyrolysis volatile products were recorded by PS/OTAB-Ti3C2 compared to pristine PS. These property enhancements of PS nanocomposites are attributed to the superior dispersion, catalytic and barrier effects of Ti3C2 nanosheets.

Synergistic Effects of Flame Retardants on the Flammability and Foamability of PS Foams Prepared by Supercritical Carbon Dioxide Foaming

Halogen-free flame-retardant polystyrene (PS) foams prepared by supercritical carbon dioxide (SC-CO₂) foaming have been achieved. The flame-retardants include expandable graphite (EG) and melamine phosphate (MP), and their influence on the foamability, decomposition behavior, fire performance, and mechanical properties of PS foams were investigated. It has been shown that flame retardants can generate inert gases and catalyze the char formation from PS, and the formed thick char layer with a notable barrier property can greatly decrease the heat release of PS foams. The addition of triphenyl phosphate (TPP) or hexaphenoxycyclotriphosphazene (HPCTP), which acts as a flame-retardant plasticizer, can obviously improve the foamability and fire performance of the foams. TPP or HPCTP can generate active phosphorous species and phenoxyl radicals to enhance the gas phase flame-retardant effect; therefore, the flame-retarded PS foams (with 25 wt % MP/EG) achieve HF1 and V-0 ratings, with limiting oxygen index (LOI) values of 30.1 or 29.6%, respectively. The numerical assessment of synergistic effects of TPP and HPCTP on further enhancing flame retardancy of PS foams has been provided by the microcalorimeter (MCC) test. Further X-ray photoelectron spectroscopy (XPS) investigation on char residues of PS foams demonstrates the formation of the P-O-C and other stable structures.

Synthesis of a DOPO-triazine additive and its flame-retardant effect in rigid polyurethane foam

A DOPO (9,10-dihydro-9-oxa-10-phosphaphen-anthrene-10-oxide)-based halogen-free flame retardant (ODOPM-CYC) was synthesized and incorporated in rigid polyurethane foam (RPUF). The structure of ODOPM-CYC was characterized by Fourier transform infrared spectra (FTIR), 1H NMR and 31P NMR. The effects of ODOPM-CYC on the flame resistance, mechanical performances, thermal properties and cell structure of RPUF were also investigated. The results showed that the incorporation of ODOPM-CYC strikingly enhanced flame retardant properties of RPUF. The flame retarded RPUF acquired a limiting oxygen index (LOI) value of 26% and achieved UL-94 V-0 rating with the phosphorus content of 3 wt%. The smoke production rate (SPR) also showed an obvious decrease and total smoke release (TSR) was 39.8% lower than that of neat RPUF. Besides, the results demonstrated that the incorporation of ODOPM-CYC provided RPUF better thermal stability but did not show any obvious influence on its thermal conductivity.

Cardanol and Eugenol Based Flame Retardant Epoxy Monomers for Thermostable Networks

Epoxy materials have attracted attention for many applications that require fireproof performance; however, the utilization of hazardous reagents brings about potential damage to human health. Eugenol and cardanol are renewable, harmless resources (according to ECHA) that allow the achievement of synthesis of novel phosphorylated epoxy monomers to be used as reactive flame retardants. These epoxy building blocks are characterized by ¹H NMR and ³¹P NMR (nuclear magnetic resonance) and reacted with a benzylic diamine to give bio-based flame-retardant thermosets. Compared to DGEBA (Bisphenol A Diglycidyl Ether)-based material, these biobased thermosets differ by their cross-linking ratio, the nature of the phosphorylated function and the presence of an aliphatic chain. Eugenol has led to thermosets with higher glass transition temperatures due to a higher aromatic density. The flame-retardant properties were tested by thermogravimetric analyses (TGA), a pyrolysis combustion flow calorimeter (PCFC) and a cone calorimeter. These analyses demonstrated the efficiency of phosphorus by reducing significantly the peak heat release rate (pHRR), the total heat release (THR) and the effective heat of combustion (EHC). Moreover, the cone calorimeter test exhibited an intumescent phenomenon with the residues of phosphorylated eugenol thermosets. Lastly, the higher flame inhibition potential was highlighted for the phosphonate thermoset.

Effects of an Organic-Inorganic Hybrid Containing Allyl Benzoxazine and POSS on Thermal Properties and Flame Retardancy of Epoxy Resin

A novel organic-inorganic hybrid containing allyl benzoxazine and polyhedral oligomeric silsesquioxane (POSS) was synthesized by the thiol-ene (click) reaction. The benzoxazine (BOZ)-containing POSS (SPOSS-BOZ) copolymerized with benzoxazine/epoxy resin was used to prepare composites of SPOSS-PBZ-E nanocomposites(NPs). The polymerization behavior was monitored by FTIR and non-isothermal differential scanning calorimetry (DSC), which showed that the composites had completely cured with multiple polymerization mechanisms according to the oxazine ring-opening and epoxy resin (EP) polymerization. The thermal properties of the organic-inorganic polybenzoxazine (PBZ) nanocomposites were analyzed by DSC and thermogravimetric analysis (TGA). Furthermore, the X-ray diffraction analysis and the scanning electron microscopy (SEM) micrographs of the SPOSS-PBZ-E nanocomposites indicated that SPOSS was chemically incorporated into the hybrid nanocomposites in the size range of 80-200 nm. The flame retardancy of the benzoxazine epoxy resin composites was investigated by limiting oxygen index (LOI), UL 94 vertical burn test, and cone calorimeter tests. When the amount of SPOSS reached 10% or more, the vertical burning rating of the curing system arrived at V-1, and when the SPOSS-BOZ content reached 20 wt %, the thermal stability and flame retardancy of the material were both improved. Moreover, in the cone calorimeter testing, the addition of SPOSS-BOZ hindered the decomposition of the composites and led to a reduction in the peak heat release rate (pHRR), the average heat release rate (aHRR), and the total heat release (THR) values by about 20%, 25%, and 25%, respectively. The morphologies of the chars were also studied by SEM and energy dispersive X-ray spectroscopy (EDX), and the flame-retardant mechanism of POSS was mainly a condensed-phase flame retardant. The ceramic layer was formed by the enrichment of silicon on the char surface. When there are enough POSS nanoparticles, it can effectively protect the combustion of internal polymers.

Synthesis of Resorcinol-Based Phosphazene-Containing Epoxy Oligomers

Phosphazene-containing epoxy-resorcinol oligomers (PERO) are synthesized in one stage with the direct interaction of hexachlorocyclotriphosphazene (HCP), resorcinol, and epichlorohydrin in the presence of solid NaOH. Depending on the initial ratio of HCP:resorcinol, PERO contains from 20 to 50 wt.% phosphazene component (2.0–4.8% of phosphorus) and have an epoxy group content up to 30 %. Products are characterized using ¹H and ³¹P NMR spectroscopy, MALDI-TOF mass spectrometry, and elemental analysis. According to mass spectrometry, the phosphazene fractions of PERO include up to 30 individual compounds with a predominance of cyclotriphosphazenes with one unsubstituted chlorine atom and four or five glycidyl groups. PERO has a lower viscosity in comparison with similar resins based on bisphenol A, which can simplify their use as a binder for polymer composites, adhesives, and paints.

Gradient-Structured Nonflammable Flexible Polymer Membranes

Herein, we report the formation and properties of a rare example of high-performance composite membranes from polybisbenzimidazobenzophenanthroline-dione (BBB) that do not sustain a flame or burn with smoke nor show melt dripping. In addition, this material possesses a low density and very high thermal stability (char yield as high as 80-94%), strength, and flexibility. Such membranes are highly desirable for battery separators, protective clothing, construction, and automobiles. Because BBB is an insoluble and infusible polymer, the composite membranes were made using a bottom-up vacuum-assisted self-assembly method with an aqueous dispersion of short BBB fibers and Hec. The use of water as the solvent, upscalability, and excellent flame retardancy in combination with low density, flexibility, and low thermal conductivity of the composite membranes make the preparation method and membranes highly promising for future use in real applications.