Novel Flame Retardants Containing 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and Unsaturated Bonds: Synthesis, Characterization, and Application in the Flame Retardancy of Epoxy Acrylates

Preparation and chromatographic evaluation of 9-oxa-10-phosphophenanthrene 10-oxide bonded phenyl stationary phase and investigation of its retention mechanism through nuclear magnetic resonance spectroscopy

BACKGROUND

In reversed-phase liquid chromatography, the C18 alkyl bonded phase, as the primary stationary phase, is widely used in pharmaceutical and food analysis. The phenyl bonded phase often serves as a complementary choice to the C18 phase to enhance the separation performance of specific categories of compounds. However, both C18 and the currently available phenyl bonded phase chromatography columns show room for further optimization in improving the separation efficiency of specific compound classes, such as dihydroflavonoids. Additionally, the potential role and impact of introducing phosphorus groups into chromatographic stationary phases have not been fully explored, indicating a promising direction for research.

RESULTS

In the present work, we prepared a novel phenyl stationary phase by bonding 9-oxa-10-phosphaphenanthrene 10-oxide onto silica gel. The obtained material was characterized by scanning electron microscopy, fourier transforms infrared spectroscopy, and elemental analysis. The results show that 9-oxa-10-phosphaphenanthrene 10-oxide was successfully bonded on the silica surface with a load of 3.90 %. Further chromatographic characterization in high-performance liquid chromatography exhibited high column efficiency (40,792 plates m-1 for the determination of biphenyl) and good stability (RSD of 0.28 %∼5.38 %). Moreover, we made a detailed study of the column separation mechanism by nuclear magnetic resonance spectroscopy titration experiment. Comparing to commercial phenyl column, the proposed stationary phase showed shorter retention time and higher throughput. In addition, the stationary phase has a strong ability to separate multiple types of compounds, which provides a new strategy for the separation of complex samples, such as active ingredients in traditional Chinese medicine.

SIGNIFICANCE

We have developed a novel phenyl column and conducted a comprehensive examination of its chromatographic performance, demonstrating excellent separation capabilities and high efficiency for both nonpolar and moderately polar aromatic compounds. Additionally, we explored the impact of phosphorus-containing groups on the separation performance of chromatographic stationary phases.

Effect of flame retardants on mechanical and thermal properties of bio-based polyurethane rigid foams

A soy oil-based polyol (HSBP) was synthesized from epoxidized soy oil through a ring-opening reaction with distilled water. A phosphorus-containing flame retardant (DOPO–HSBP) was synthesized through the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and HSBP. A nitrogen-containing flame retardant (T–D) was prepared by the reaction of diethanolamine with glycol diglycidyl ether. The structures of HSBP, DOPO–HSBP, and T–D were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (¹H NMR). The flame-retardant rigid polyurethane foam (PPUFs and NPUFs) was prepared successfully by mixing HSBP, DOPO–HSBP, and T–D. The effects of DOPO–HSBP content on the mechanical, thermal, and flame-retardant properties of PPUFs and NPUFs were investigated by tensile tests, thermogravimetric analyses (TGA), limiting oxygen index (LOI), and UL-94 vertical burning level. The morphology of PPUFs and NPUFs was studied via scanning electron microscopy (SEM). With the increase in the percentage of DOPO–HSBP added, the flame retardant property of rigid polyurethane foam (RPUF) was greatly improved. When the phosphorus-containing flame retardant DOPO–HSBP was added to 50% of the RPUF with the nitrogen-containing flame retardant T–D, the LOI value of the foam increased from 18.3 to 25.5, and the UL-94 result was classified as “V-0” with almost no effect on the mechanical properties of the RPUF. The results showed that the phosphorus and nitrogen synergistic flame retardants of DOPO–HSBP and T–D can endow excellent flame retardant properties to RPUF without affecting its mechanical properties.

A vegetable oil-based polyurethane rigid foam containing a phosphorus–nitrogen dualflame retardant system was prepared, and the foam exhibited not only excellent flame retardant properties but also good mechanical properties.

Zinc-Catalyzed Phosphonylation of Alcohols with Alkyl Phosphites

In the presence of a catalytic amount of either Zn(acac)₂ or bis(2,2,6,6-tetramethyl-3,5-heptanedionato)zinc(II) (Zn(TMHD)₂), primary, secondary, and tertiary alcohol substituents on a wide range of substrates, including acyclic and cyclic structures, carbohydrates, steroids, and amino acids, reacted with dimethyl phosphite to afford the corresponding H-phosphonate diesters in high to excellent yields.

Synthesis of DOPO-HQ-functionalized graphene oxide as a novel and efficient flame retardant and its application on polylactic acid: Thermal property, flame retardancy, and mechanical performance

The fabrication of biodegradable polymer nanocomposites with improved flame retardancy has been an urgent task in practical because of the huge benefits of biodegradable polymers. In this work, 10-(2,5-dihydroxyl phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ)-functionalized graphene oxide (GO) (FGO-HQ) was used as a novel and highly efficient flame retardant (FR) to improve the flame retardancy of polylactide (PLA) nanocomposites. Contributed by the bi-phase flame retardant action, including the physical barrier char in solid phase and the decreased flammable volatiles in gas phase, the resultant PLA/FGO-HQ nanocomposites presented excellent flame resistance at the loading of 6 wt% FR: UL-94 reached V-0 rating; peak heat release rate (PHRR) and total heat release (THR) decreased by 24.0% and 43.0%, respectively; smoke production rate (SPR) and total smoke release (TSR) decreased by 46% and 83%, respectively. For further confirming its flame-resistance mechanism, thermogravimetric analysis/infrared spectrometry (TG-IR) and Fourier transform infrared spectra (FT-IR), scanning electron microscope (SEM), and Raman spectroscopy were employed. Results indicated that the incorporation of FGO-HQ can effectively reduce the evaporation of flammable gaseous product in gas phase through quenching free radicals. Meanwhile, graphitized carbons are formed in the residual char and PLA/FGO-HQ sample can achieve a good thermal stability in the combustion with phosphorus-containing compounds and aromatic structure in the solid phase. Furthermore, the tensile strength of PLA nanocomposites presented good mechanical properties with the addition of FR as well. These results suggested that the incorporation of FGO-HQ FR not only improve the flame retardancy and thermal stability of biodegradable polymer nanocomposites but also without sacrificing their mechanical properties.

Superior flame retardancy and smoke suppression of epoxy-based composites with phosphorus/nitrogen co-doped graphene

Phosphorus and/or nitrogen doping is an effective method of improving the physical and chemical properties of reduced graphene oxide (rGO). In this work, phosphorus and nitrogen co-doped rGO (PN-rGO), synthesized using a scalable hydrothermal and microwave process, was used as an additive to improve the flame retardancy of epoxy resin (EP) for the first time. Chemical structure and morphology characterization confirmed that the nitrogen and phosphorus atoms were doped into the graphite lattice adopting pyrrolic-N, pyridinic-N, quaternary-N and pyrophosphate and metaphosphate forms. Doping increased the oxidization resistance of rGO and the thermal-oxidative stability of its composites' char, while also improving the catalytic charring ability of polymer. Both effects resulted in the formation of a stable char protective layer during burning and to a significant improvement in flame retardation and smoke suppression in the final composites. The peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) for the EP-based composite (containing 5 wt% PN-rGO) decreased by 30.9%, 29.3% and 51.3%, respectively, compared to neat EP. Our work has produced a promising graphene-based flame retardant additive for the mass production of high-performance composites, also expended the application of heteroatom-doped graphene.

Two high-efficient DOPO-based phosphonamidate flame retardants for transparent epoxy resin

In this work, two kinds of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based phosphonamidate flame retardants named 4,4′-diamino-diphenyl methane (DDM)-DOPO and morpholine (MPL)-DOPO are successfully synthesized by the classic Atherton–Todd reaction, and their chemical structures are characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Epoxy composites containing DDM-DOPO or MPL-DOPO are prepared, which still retain relatively high transparency compared with pure epoxy resin (EP). Its fire behavior is studied in terms of vertical burning test (UL-94), limiting oxygen index (LOI), and cone calorimeter tests. The LOI values can achieve 30% and UL-94 test past V-0 rating for DDM-DOPO-modified epoxy composites with 0.25 wt% phosphorus content. The cone calorimeter results indicate that the modified epoxy composites can release less heat and smoke compared with pure EP. Also, thermal degradation behavior and flame-retardant mechanism of epoxy composites are investigated by thermogravimetric analysis and thermogravimetric analysis/infrared spectrometry. The results indicate that two DOPO-based phosphonamidates show a significant gaseous-phase effect on reducing the release of combustible volatiles.

Novel flame retardancy effect of phenethyl-bridged DOPO derivative on epoxy resin

A series of flame-retardant epoxy resins (EPs) containing either phenethyl-bridged 9 or 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative (bisDOPO) were prepared. The flame-retardant properties of bisDOPO on EP composites were characterized by the limiting oxygen index (LOI), the UL-94 vertical burning, and the cone calorimeter test (CCT).The LOI of the EP/bisDOPO composites increased from 21.8% to 38.0%, and the hybrids with the 10 wt% bisDOPO obtained a V-0 rating in the UL94 vertical burning test. The char residue following the CCT showed intumescent structures with continuous and compact surfaces that can effectively suppress the spread of the flame and extinguish the fire. This was confirmed through both visual observation and scanning electron microscopy (SEM) measurements. The flame-retardant mechanism was studied by Fourier transform infrared spectroscope (FTIR), thermogravimetric analysis/infrared spectrometry, SEM/energy-dispersive X-ray, and pyrolysis-gas chromatography/mass spectrometry. Overall, bisDOPO was an effective flame retardant with potential applications within EP.

Flame-retardant effect of a phenethyl-bridged DOPO derivative and layered double hydroxides for epoxy resin

Flame-retardant epoxy resin (EP) composites were prepared by the incorporation of a phenethyl-bridged DOPO derivative (DiDOPO) and modified layered double hydroxide (OLDH).

Novel phosphorus–nitrogen–silicon flame retardants and their application in cycloaliphatic epoxy systems

In this work, we prepared two novel reactive-type halogen-free and UV-curable phosphorus–nitrogen–silicon synergistic flame retardants.