Gas-phase Activation Research Articles

Coumarin-DPPO a new bio-based phosphorus additive for poly(lactic acid): Processing and flame retardant application

This study addresses very important aspects of the sustainable development of new flame retardant materials: (i) the preparation of a novel flame retardant (FR) additive from bio-resource, (ii) its use as FR additive in poly(lactic acid) (PLA) based composites and, (iii) the in vitro toxicity assessment of the FR. The synthesis of this bio-based FR additive was achieved through a phospha-Michael addition of diphenylphosphine oxide (DPPO) and the naturally occurring compound coumarin, yielding 4-(diphenylphosphoryl)chroman-2-one (CU-DPPO). The flame-retarded CU-DPPO PLA composites were prepared either via conventional melt blending of commercially available PLA or through reactive extrusion (REX) of L-lactide. Characterization of the composites was performed through nuclear magnetic resonance (NMR), size exclusion chromatography (SEC) and thermogravimetric analysis (TGA). TGA analysis of the FR-PLA composites showed an increase in thermal stability, confirming the beneficial effect of the CU-DPPO additive. Direct insertion probe mass spectrometry (DIP-MS) analysis was used to gain insight on the mechanism of action of the FR additive, suggesting gas-phase activity. Rheological measurements exhibited the thermo-oxidative stabilizing effect in the modified PLA. The flame retardancy of the melt-blended PLA composites with CU-DPPO was investigated by limited oxygen index (LOI), cone calorimetry and vertical burning tests (UL 94 and BKZ-VB). Samples containing 10 wt.% of CU-DPPO showed improved fire performance with a limiting oxygen index (LOI) of 29%, passing Swiss vertical burning test (BKZ-VB) and obtaining a V-0 rating in the UL 94 test. Moreover, a preliminary toxicity assessment of the CU-DPPO, carried out using an established in vitro platform, showing no adverse effects on cell viability.

Boron Carbonitride Films with Tunable Composition: LPCVD and PECVD Synthesis Using Trimethylamine Borane and Nitrogen Mixture and Characterization

This study reports the chemical vapor deposition of amorphous boron carbonitride films on Si(100) and SiO2 substrates using a trimethylamine borane and nitrogen mixture. BCxNy films with different compositions were produced via variations in substrate temperature and type of gas-phase activation. The low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) methods were used. The “elemental composition—chemical bonding state—properties” relationship of synthesized BCxNy was systematically studied. The hydrophilicity, mechanical, and optical properties of the films are discussed in detail. The composition of films deposited by the LPCVD method at temperatures ranging from 673 to 973 K was close to that of boron carbide with a low nitrogen content (BCxNy). The refractive index of these films changed in the range from 2.43 to 2.56 and increased with temperature. The transparency of these films achieved 85%. LPCVD films were hydrophilic and the water contact angles varied between 53 and 63°; the surface free energy was 42–48 mN/m. The microhardness, Young’s modulus and elastic recovery of LPCVD films ranged within 24–28 GPa, 220–247 GPa, and 70–74%, respectively. The structure of the PECVD films was close to that of hexagonal boron nitride, and their composition can be described by the BCxNyOz:H formula. In case of the PECVD process, the smooth films were only produced at low deposition temperatures (373–523 K). The refractive index of these films ranged from 1.51 to 1.67. The transparency of these films achieved 95%; the optical band gap was evaluated as 4.92–5.28 eV. Unlike LPCVD films, they were very soft, and their microhardness, Young’s modulus and elastic recovery were 0.8–1.4 GPa, 25–26 GPa, and 19–28%, respectively. A set of optimized process parameters to fabricate LPCVD BCxNy films with improved mechanical and PECVD films with high transparency is suggested.

The effects of various flame retardants on the combustion of polypropylene: Combining optical diagnostics and pyrolysis fragment analysis

The assessment of the efficacy and mode of action of flame retardants in polymers requires a thorough knowledge of the coupling of the presence of chemical inhibitors with the underlying heat and mass transport processes. In this experimental work, we combine a thermal decomposition analysis with optical combustion diagnostics in different test environments to gain a comprehensive understanding of the relevant sub-processes and demonstrate how this approach provides future opportunities for the research regarding the mode of action of flame retardants. Four different composites of polypropylene (PP) and 10 wt% of selected flame retardants as well as neat PP are prepared. Flame retardants include pentaerythritol spirobis(methylphosphonate) (PSMP), zinc diethylphosphinate (DEPZn), aluminum hydroxide (i.e. aluminum trihydrate, ATH) and ammonium polyphosphate (APP). The released substances in the gas phase are investigated by using thermogravimetric analysis coupled to Fourier-transform infrared spectroscopy (TGA-FTIR), and the burning behavior regarding carbon monoxide concentration and heat release rate (HRR) is studied in cone calorimeter experiments. The ignition and combustion of flame retarded micrometer-sized particles of PP are experimentally investigated in a laminar flat flame burner by means of simultaneous scanning planar laser-induced fluorescence of OH radicals (OH-PLIF) and diffuse back-illumination (DBI) at a repetition rate of 10 kHz. Particles with gas-phase activity show a decreased normalized OH signal intensity during combustion. A dependency of the dimensionless flame radius on the particle size is found which can be linked to the faster heating and pyrolysis of smaller particles compared to large particles and agglomerations. Eventually, the interaction with an external premixed flame and the subsequent extinction of self-sustaining flames of polymer sticks is investigated using OH-PLIF in an adapted horizontal burning test suited for the application of optical diagnostics. This approach allows to link the findings of investigations encompassing multiple scales, resulting in a thorough understanding of both polymer chemistry and combustion dynamics in flame retarded polymers.

Mechanisms for Catalytic CO Oxidation on SiAun (n = 1-5) Cluster.

Significant progress has been made in understanding the reactivity and catalytic activity of gas-phase and loaded gold clusters for CO oxidation. However, little research has focused on mixed silicon/gold clusters (SiAun) for CO oxidation. In the present work, we performed density function theory (DFT) calculations for a SiAun (n = 1-5) cluster at the CAM-B3LYP/aug-cc-pVDZ-PP level and investigated the effects on the reactivity and catalytic activity of the SiAun cluster for CO oxidation. The calculated results show that the effect is very low for the activation barriers for the formation of OOCO intermediates on SiAu clusters, SiAu3 clusters, and SiAu5 clusters in the catalytic oxidation of CO and the activation energy barriers for the formation of OCO intermediates on OSiAu3, OSiAu4, and OSiAu5. Our calculations show that, compared with the conventional small Au cluster, the incorporation of Si enhances the catalytic performance towards CO oxidation.

Insights into the role of water and surface OH species in methane activation on copper oxide: a combined theoretical and experimental study

An integrated theoretical and experimental investigation reveals how the presence of water alters the activity of metal oxide catalysts in gas-phase activation and conversion of methane.

Group 6 germylidyne complexes in the gas phase by LIFDI and APCI mass spectrometry.

Although showing fascinating chemical properties and reactivity in solution, heavier tetrelylidyne complexes with M≡E triple bonds have not been studied in the gas phase before due to their high sensitivity towards air and moisture. We selected four group 6 germylidyne complexes, [Cp(PMe3)2M≡GeArMes] (M = Mo (1-Mo), W (1-W), ArMes = 2,6-dimesitylphenyl) and [Tp'(CO)2M≡GeArMes] (M = Mo (2-Mo), W (2-W), Tp' = κ3-N,N',N''-hydridotris(3,5-dimethylpyrazolyl) borate), for a mass-spectrometric study. Liquid Injection Field Desorption Ionization (LIFDI) proved to be a well-suited technique to ionize these sensitive compounds as the spectra show the molecular ions as radical cations and only minor traces of fragmentation or degradation products. In addition, Atmospheric Pressure Chemical Ionization (APCI) connected to a high-resolving tandem mass spectrometer allowed us to study the gas-phase fragmentation behaviour of these compounds. The fragmentation patterns not only comprise the expected losses of phosphane or carbonyl ligands, respectively, but also indicate C-H bond activation by the electron-deficient metal centre. An enhanced reactivity of the tungsten species is visible in a preferred methyl abstraction in the phosphane complex 1-W compared to 1-Mo. Although degradation in solution before ionization obviously can destroy the M≡Ge triple bond, the cleavage of the M≡Ge bond upon gas-phase activation is not observed for the Mo species and only as a minor pathway for the W compounds, highlighting the high bonding energy between metal and tetrel.

Porous structure features of carbon materials with extended-surface

The article provides a general overview of the production methods and applications of carbon materials with a large specific surface area. The following materials were taken as objects for the study: SK-AG-3 granular activated carbon produced by OJSC «Sorbents of Kuzbass», Kemerovo, activated cellulose fiber produced by the Krasnoyarsk Chemical Fiber Plant after carbonation, graphitization, and gas-phase activation at 900 °C in carbon dioxide current, Busofit-T carbon fabric produced by OJSC «SvetlogorskKhimvolokno», thermally expanded fluorinated graphite produced by OJSC «Siberian Chemical Combine». The porous structure of these materials was investigated by low-temperature volumetric nitrogen adsorption at the ASAP 2020 unit. Nitrogen adsorption-desorption isotherms were recorded in a relative pressure range of p/p0 = 0.05÷1.0 at 77 K. The specific surface area was estimated by the BET method based on the adsorption isotherm at p/p0 = 0.05÷0.30. The specific surface area was 485, 1241, 1156 and 290.5 m2/g for activated carbon, activated carbon fibers, Busofit-T fabric and thermally expanded graphite, respectively. The volume of mesopores and their size distribution were calculated by the Barrett-Joyner-Нalenda (BJH) method in a pressure range of p/p0 = 0.35÷0.95. The volume of micropores and their size distribution were calculated by the Horvath-Kawazoe method using the nitrogen adsorption-desorption isotherm in a relative pressure range of p/p0 = 0.00÷0.01. These methods were also used to determine the average diameter of mesopores and micropores. A comparative analysis of the results obtained was carried out. A relationship between the internal structure of the investigated materials and the porous structure properties was traced. It was shown that activated carbon, fibers, and carbon fabrics are microporous materials, and thermally expanded graphite has a mesoporous structure.

Investigation of Charge-State-Dependent Compaction of Protein Ions with Native Ion Mobility-Mass Spectrometry and Theory.

The precise relationship between native gas-phase protein ion structure, charge, desolvation, and activation remains elusive. Much evidence supports the Charge Residue Model for native protein ions formed by electrospray ionization, but scaling laws derived from it relate only to overall ion size. Closer examination of drift tube CCSs across individual native protein ion charge state distributions (CSDs) reveals deviations from global trends. To investigate whether this is due to structure variation across CSDs or contributions of long-range charge-dipole interactions, we performed in vacuo force field molecular dynamics (MD) simulations of multiple charge conformers of three proteins representing a variety of physical and structural features: β-lactoglobulin, concanavalin A, and glutamate dehydrogenase. Results from these simulated ions indicate subtle structure variation across their native CSDs, although effects of these structural differences and long-range charge-dependent interactions on CCS are small. The structure and CCS of smaller proteins may be more sensitive to charge due to their low surface-to-volume ratios and reduced capacity to compact. Secondary and higher order structure from condensed-phase structures is largely retained in these simulations, supporting the use of the term "native-like" to describe results from native ion mobility-mass spectrometry experiments, although, notably, the most compact structure can be the most different from the condensed-phase structure. Collapse of surface side chains to self-solvate through formation of new hydrogen bonds is a major feature of gas-phase compaction and likely occurs during the desolvation process. Results from these MD simulations provide new insight into the relationship of gas-phase protein ion structure, charge, and CCS.

Gas-phase CO2 activation with single electrons, metal atoms, clusters, and molecules

In this review, the history and outlook of gas-phase CO2 activation using single electrons, metal atoms, clusters (mainly metal hydride clusters), and molecules are discussed on both of the experimental and theoretical fronts. Although the development of bulk solid-state materials for the activation and conversion of CO2 into value-added products have enjoyed great success in the past several decades, this review focuses only on gas-phase studies, because isolated, well-defined gas-phase systems are ideally suited for high-resolution experiments using state-of-the-art spectrometric and spectroscopic techniques, and for simulations employing modern quantum theoretical methods. The unmatched high complementarity and comparability of experiment and theory in the case of gas-phase investigations bear an enormous potential in providing insights in the reactions of CO2 activation at the atomic level. In all of these examples, the reduction and bending of the inert neutral CO2 molecule is the critical step determined by the frontier orbitals of reaction participants. Based on the results and outlook summarized in this review, we anticipate that studies of gas-phase CO2 activations will be an avenue rich with opportunities for the rational design of novel catalysts based on the knowledge obtained on the atomic level.

Retro Diels-Alder Fragmentation of Fulvene-Maleimide Bioconjugates for Mass Spectrometric Detection of Biomolecules.

Diels-Alder chemistry is a well-explored avenue for the synthesis of bioactive materials; however, its potential applications have recently expanded following the development of reactions that can be performed in buffered aqueous environments at low temperatures, including fulvene-maleimide [4 + 2] cycloadditions. In this study, we synthesized two novel amine-reactive fulvene linkers to demonstrate the application of this chemistry for generating mass spectrometry-cleavable labels ("mass tags"), which can be used for the labeling and detection of proteins. Successful conjugation of these linkers to maleimide-labeled peptides was observed at low temperatures in phosphate-buffered saline, allowing the non-destructive modification of proteins with such mass tags. The labile nature of fulvene-maleimide adducts in the gas phase also makes them suitable for both matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometric analysis. Unlike previous examples of MALDI mass tags, we show that fulvene-maleimide cycloaddition adducts fragment predictably upon gas-phase activation without the need for bulky photocleavable groups. Further exploration of this chemistry could therefore lead to new approaches for mass spectrometry-based bioassays.

Bicarbonate buffers can promote crosslinking and alternative gas-phase dissociation pathways for multiprotein complexes

Previously, we have reported the stabilization effect of Hofmeister salts for multiprotein complexes (MPC) in the absence of bulk solvent (J. Am. Chem. Soc.2011,133 (29), 11,358–11367; Angew. Chem. Int. Ed.2012,51 (23), 5692–5695; Angew. Chem. Int. Ed.2013, 52 (32), 8329–8332.). Our efforts sought to bridge the gap between gas-phase protein structures and those found in solution. To reveal more detailed MPC topology information, native ion mobility-mass spectrometry (IM-MS) measurements are often combined with gas-phase activation methods. Conventional activation methods, including collision induced dissociation/unfolding (CID/CIU), however, primarily report information focused on monomeric subunits within the MPC, limiting the topological information obtained. Herein, we describe a simple buffer-doping method that promotes an alternative MPC CID pathway which readily produces product ions that correspond to larger sub-complexes from within some parent assemblies. Interestingly, tetramers exhibiting a dimer of dimers quaternary structure (e.g. hemoglobin and concanavalin A) produce dimeric product ions upon collisional activation following ionization from bicarbonate buffer, in contrast to the commonly observed monomer-ejection CID pathway. In order to both further investigate and validate our native IM-MS, we performed bottom-up proteomics experiments on MPCs housed in bicarbonate buffer. Our efforts revealed evidence of bicarbonate-mediated disulfide bond formation in proximal Cystine residues. We close by discussing the applications for these observations in the context of MPC structure determination by native IM-MS.

Native mass spectrometry and gas-phase fragmentation provide rapid and in-depth topological characterization of a PROTAC ternary complex

Proteolysis-targeting chimeras (PROTACs) represent a new direction in small-molecule therapeutics whereby a heterobifunctional linker to a protein of interest (POI) induces its ubiquitination-based proteolysis by recruiting an E3 ligase. Here, we show that charge reduction, native mass spectrometry, and gas-phase activation methods combine for an in-depth analysis of a PROTAC-linked ternary complex. Electron capture dissociation (ECD) of the intact POI-PROTAC-VCB complex (a trimeric subunit of an E3 ubiquitin ligase) promotes POI dissociation. Collision-induced dissociation (CID) causes elimination of the nonperipheral PROTAC, producing an intact VCB-POI complex not seen in solution but consistent with PROTAC-induced protein-protein interactions. In addition, we used ion mobility spectrometry (IMS) and collisional activation to identify the source of this unexpected dissociation. Together, the evidence shows that this integrated approach can be used to screen for ternary complex formation and PROTAC-protein contacts and may report on PROTAC-induced protein-protein interactions, a characteristic correlated with PROTAC selectivity and efficacy.

Experimental Determination of Activation Energies for Covalent Bond Formation via Ion/Ion Reactions and Competing Processes.

The combination of ion/ion chemistry with commercially available ion mobility/mass spectrometry systems has allowed rich structural information to be obtained for gaseous protein ions. Recently, the simple modification of such an instrument with an electrospray reagent source has allowed three-dimensional gas-phase interrogation of protein structures through covalent and noncovalent interactions coupled with collision cross section measurements. However, the energetics of these processes have not yet been studied quantitatively. In this work, previously developed Monte Carlo simulations of ion temperatures inside traveling wave ion guides are used to characterize the energetics of the transition state of activated ubiquitin cation/sulfo-benzoyl-HOAt reagent anion long-lived complexes formed via ion/ion reactions. The ΔH‡ and ΔS‡ of major processes observed from collisional activation of long-lived gas-phase ion/ion complexes, namely collision induced unfolding (CIU), covalent bond formation, or neutral loss of the anionic reagent via intramolecular proton transfer, were determined. Covalent bond formation via ion/ion complexes was found to be significantly lower energy compared to unfolding and bond cleavage. The ΔG‡ values of activation of all three processes lie between 55 and 75 kJ/mol, easily accessible with moderate collisional activation. Bond formation is favored over reagent loss at lower activation energies, whereas reagent loss becomes competitive at higher collision energies. Though the ΔG‡ values between CIU of a precursor ion and covalent bond formation of its ion/ion product complex are comparable, our data suggest covalent bond formation does not require extensive isomerization.

Native Mass Spectrometry and Gas-Phase Fragmentation Provide Rapid and In-Depth Topological Characterization of a PROTAC Ternary Complex

SummaryProteolysis targeting chimeras (PROTACs) represent a new direction in small-molecule therapeutics whereby a heterobifunctional linker to a protein-of-interest (POI) induces its ubiquitination-based proteolysis via recruiting an E3 ligase. We show here that native mass spectrometry and associated gas-phase activation methods combine for an in-depth analysis of a PROTAC-linked ternary complex. Electron-capture dissociation (ECD) of the intact POI-PROTAC-VCB complex (a trimeric subunit of an E3 ubiquitin ligase) promotes significant PROTAC ejection in competition with minor POI dissociation. Collision-induced dissociation (CID) causes elimination of the non-peripheral PROTAC, producing an intact VCB-POI complex not seen in solution but consistent with PROTAC-induced protein-protein interactions. We further used ion mobility spectrometry (IMS) and collisional activation to identify the source of this unexpected dissociation. Together, the evidence shows that this integrated approach can be used to screen for ternary complex formation, PROTAC-protein contacts, and PROTAC-induced protein-protein interactions, a characteristic correlated with PROTAC selectivity and efficacy.

A molecularly engineered bioderived polyphosphate for enhanced flame retardant, UV-blocking and mechanical properties of poly(lactic acid)

Polylactic acid (PLA) represents one of most promising bioplastics in response to the increasing global microplastics pollution issue facing the entire ecosystem. Nevertheless, PLA is inherently flammable and also prone to UV-light attack, significantly restricting its wide applications in packaging, fibers and electronics industry. Despite high effectiveness in PLA, existing polyphosphate-based flame retardants are usually synthesized mainly from non-degradable petrochemical compounds and their functions are limited to improving flame retardancy of the polymeric matrix. We, herein, report the synthesis of a novel multifunctional bioderived polyphosphate (PPD) for PLA by using plant-derived diphenolic acid as a starting material. Our results reveal that the addition of 6 wt% of PPD enables PLA to achieve a desirable UL-94V-0 rating and a high LOI value of 27.1% due to its high gas-phase activity, which means that the final PLA fully meets the demanding flame retardancy requirement in industry. Moreover, the resultant flame-retardant PLA shows a high ultraviolet protection factor (UPF) value of 403, which indicates its excellent UV protection capability. Because of the fine and uniform dispersion of PPD within the resin matrix and their strong interfacial interactions, the PLA/6% PPD shows a 31% increase in impact toughness and a slight improvement in tensile strength compared to the bulk PLA. This work provides a strategy to synthesize a multifunctional bio-based polyphosphate flame retardant, which holds great promise for extending the practical applications of PLA with excellent flame retardancy, UV-blocking and mechanical performances.

Digital ion trap mass analysis of high mass protein complexes using IR activation coupled with ion/ion reactions

Native mass spectrometry (MS) focuses on measuring the masses of large biomolecular complexes and probing their structures. Large biomolecular complexes are readily introduced into mass spectrometers as gas-phase ions using electrospray ionization (ESI); however, the ions tend to be heavily adducted with solvent and salts, which leads to mass measurement errors. Various solution clean-up approaches can reduce the degree of adduction prior to introduction to the mass spectrometer. Gas-phase activation of trapped ions can provide additional adduct reduction, and charge reduction ion/ion reactions increase charge state separation. Together, gas-phase activation and charge reduction can combine to yield spectra of well separated charge states for improved mass measurements. A simple gas-phase collisional activation technique is to apply a dipolar DC (DDC) field to opposing electrodes in an ion trap. DDC activation loses its efficacy when ions are trapped at low q values, which is true of the high m/z ions generated by charge reduction ion/ion reactions. Digital ion trapping (DIT) readily traps high m/z ions at higher q values by varying trapping frequency rather than amplitude, but the low frequencies used to trap high m/z ions also decreases the efficacy of DDC activation. We demonstrate here using ions derived from GroEL that IR activation of ions shows no discrimination against high m/z ions trapped with DIT, because they can be focused equally well to the trap center to interact with the IR laser beam. Following pump out of excess background gas, IR activation can also induce efficient dissociation of the GroEL complex. This work demonstrates that IR activation is an effective approach for ion heating in native MS over the unusually wide range of charge states accessible via gas-phase ion/ion reactions.

Can an Elusive Platinum(III) Oxidation State be Exposed in an Isolated Complex?

Platinum(IV) complexes are extensively studied for their activity against cancer cells as potential substitutes for the widely used platinum(II) drugs. PtIV complexes are kinetically inert and need to be reduced to PtII species to play their pharmacological action, thus acting as prodrugs. The mechanism of the reduction step inside the cell is however still largely unknown. Gas-phase activation of deprotonated platinum(IV) prodrugs was found to generate products in which platinum has a formal +3 oxidation state. IR multiple photon dissociation spectroscopy is thus used to obtain structural information helping to define the nature of both the platinum atom and the ligands. In particular, comparison of calculations at DFT, MP2 and CCSD levels with experimental results demonstrates that the localization of the radical is about equally shared between the dxz orbital of platinum and the pz of nitrogen on the amino group, the latter acting as a non-innocent ligand.

Multifunctional marine bio-additive with synergistic effect for non-toxic flame-retardancy and anti-microbial performance

Flame-retardants and biocides are well-established functional additives that enhance key properties of polymer and porous materials. Conventional additives and their secondary emissions may render materials hazardous in the long-term, incrementing human exposure to a toxic load of persistent bio-cumulative substances in the indoor built environment. The present study developed a novel multifunctional green additive formulated for the optimization of thermoplastic-lignocellulose hybrid sheet materials engineered for indoor building applications. The compound was developed from two marine bio-materials, Kelp Macroalgae (Eklonia spp.) and Bivalve mollusc shells (Veneridae spp.), selected due to their exceptional properties for these functions, as result of the complex mixture of biogenic carbonate/halide/oxide inorganic phases intricately connected through a hierarchical structure. Oxidative flame propagation was investigated under fire conditions and thermal degradation coupled with gas analysis was investigated under inert gas purge for the temperature range 30–1300 °C. The microbial biomass was analysed with culture-dependent and independent methods. The marine panel prototypes exhibited superior flame-retardant characteristics as result of synergistic mechanisms occurring at the solid-gas interface through the disruption of volatiles flame reactions in the gas-phase, endothermic reactions, and self-catalytic activation. This resulted in self-extinguishing, flame-inhibition, slow-flame propagation rate; and the formation of hierarchically porous carbonaceous phase of high-adsorptive capacity. The biodegradation and ecotoxicity analyses indicated very low-moisture absorption and a possible inhibitory effect on microbial development due to the CaCO3/alginate destabilizing effect on the cell membrane. This promising result demonstrates that the synergistic effect of the marine additive has high-potential rendering the novel hybrid materials non-toxic, biodegradation resistant, whilst increasing the recyclability potential at their end-of-life.

An efficient organic/inorganic phosphorus–nitrogen–silicon flame retardant towards low-flammability epoxy resin

In this paper, an organic/inorganic phosphorus–nitrogen–silicon flame retardant (DPHK) was synthesized by Kabachnik-Fields reaction and the sol-gel method, then it was used as a reactive flame retardant to prepare flame-retardant and smoke-suppressant epoxy resins (EP). The influence of DPHK on the flame retardancy of EP was investigated by limiting oxygen index (LOI), vertical burning test (UL-94 V) and cone calorimeter (CC) test. The results revealed that the EP containing only 3 wt% DPHK achieved UL-94 V-0 rating, and the corresponding LOI value reached 29%. Furthermore, the cone calorimeter results demonstrated that the DPHK effectively reduced the heat release rate (HRR) and total release rate (THR) of the EP. Compared with EP, the peak of heat release rate (PHRR) and THR of 4%DPHK-EP reduced by 36% and 30%, respectively. More importantly, the incorporation of DPHK suppressed the release of toxic fuel (CO) and smoke of EP, meanwhile, the increased char residue and CO/CO2 ratio of the DPHK-EP samples proved that DPHK presented not only the condensed-phase activity but also gas-phase activity. Furthermore, the involved gases and char residues were studied by using thermogravimetric analysis coupled with coupled with Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), scanning electronic microscope together with the energy dispersive X-ray spectrometer (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results certified the charring effect of the phosphaphenanthrene group and the enhancing effect of the silicon group. Subsequently, the flame inhibition effect and lesser combustible gases release enhanced the flame-retardant properties of EP.

1-Dopyl-1,2-(4-hydroxyphenyl)ethene: A flame retardant hardner for epoxy resin

Treatment of desoxyanisoin with 9,10-dihydro-9-oxaphosphaphenathrene-10-oxide (DOPO) in the presence of an acid catalyst generates an adduct, 1-dopyl-1,2-(4-methoxyphenyl)ethene which may be readily converted to the corresponding diphenolic compound, 1-dopyl-1,2-(4-hydroxyphenyl)ethene (BDE). This material behaves as an effective curing agent for the diglycidyl ether of bisphenol A (DGEBA) to provide a thermally stable (Tdec 417 °C) resin with Tg of 146 °C. This polymer displays outstanding flammability characteristics – an LOI of 36 (compared to 19 for conventionally cured resin), a total heat release of 20 kJ/g and a UL 94 V0 rating. The flame retardant impact of the incorporation of this hardner into the resin is due both to its structure (promotes char formation for solid phase activity) and the presence of the DOPO substituent (promotes gas-phase activity).