Synthesis of DOPO‐based pyrazine derivative and its effect on flame retardancy and thermal stability of epoxy resin

Abstract

A novel DOPO-based pyrazine derivative 6-((2-hydroxyphenyl)(pyrazin-2-ylamino) methyl)dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DHBAP) was triumphantly synthesized by a two-step addition reaction using 2-aminopyrazine, 2hydroxybenzaldehyde and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as reactants, and characterized by Fourier-transform infrared (FTIR), 31 P nuclear magnetic resonance (NMR) and 1 H NMR. Afterwards, the addition type flame retardant (DHBAP) was utilized to modify epoxy resin (EP) by blending method.When the content of DHBAP in neat EP was 8 wt%, it reached to the V-0 rating and the limited oxygen index (LOI) value up to 34.0%. Furthermore, according to the cone calorimeter (CC) test results, the heat release rate (HRR), total heat release (THR), smoke produce rate (SPR) and total smoke production (TSP) of EP/8% DHBAP decreased by 26.3%, 21.3%, 37.0% and 60.9% when compared with neat EP, respectively, indicating that DHBAP had good inhibition on heat and smoke releases. Eventually, the flame-retardant mechanism of DHBAP was further explored by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results showed that DHBAP had good flame-retardant activity in the gasous-condensed two phases. KEYWORDSDOPO, epoxy resin, flame retardancy, mechanism, pyrazine 1 | INTRODUCTION Epoxy resin (EP) has extensive applications in automotive, defense, aerospace, and electrical industry because of good mechanical properties and chemical stability. 1-4 Unfortunately, EP is a flammable material, which limits its further application. Consequently, it is an important task to impart flame retardancy of EPs.So as to improve its flame-retardant properties, the combination of flame retardant with EP has been recognized to be an effective way.Traditionally, halogen-containing flame retardants are widely utilized because of their gaseous phase activity. 5-7 However, halogenated retardants can produce lots of smoke and toxic gases when they are burning, which have many negative effects on the environment and human. 8,9 In recent years, researchers have developed many types of halogen-free flame retardants, such as boron, 10-13 phosphorus, [14][15][16][17][18][19] silicon, 20-22 sulfur, 23-26 graphene 27,28 and nitrogen-containing compounds. 29-31 Among them, phosphorus-containing flame retardant is the most widely used because of its good gaseous phase effect. 15,[32][33][34] Currently, DOPO and its derivatives are widely concerned for their excellent flame-retardant efficiency. Since DOPO has an active P-H group, it is easy to cleave to form H· and DOPO radicals, and can be used as an antioxidant by quenching oxygen radicals. 35,36 Due to the active group in DOPO, DOPO can react with compounds containg unsaturated bonds, such as schiff base, carbon carbon double bond and ketone, leading to various approaches to synthesize new DOPO derivatives. 37 Schäfer et al added DOPO to the EP, and the sample passed the V-0 rating, whereas the phosp...

Low flammability and smoke epoxy resins with a novel DOPO‐based imidazolone derivative

“…As shown in Figure 2A, the multi-peaks at 10 to 10. existence of chiral carbon atoms. 33 The above NMR results further confirmed that the target product DHI was successfully synthesized.…”

“…According to the literature, the synergistic systems such as DOPO/maleimide, 23,24 DOPO/silsesquioxane, [25][26][27] DOPO/ cyclotriphosphazene 28,29 and DOPO/triazine, [30][31][32] Figure 1 showed IR spectra of DOPO and DHI. As to DOPO, the characteristic peak at 2436 cm −1 was attributed to P-H bond, 33 which was observed to disappear significantly for DHI, indicating DOPO had successfully participated in reaction. Moreover, the peaks at 3435, 3300, 1685 and 1477 cm −1 were attributed to -OH, N-H bond, imidazoline ring and benzene ring, respectively.…”

A novel nitrogen, phosphorus, and boron ionic pair compound toward fire safety and mechanical enhancement effect for epoxy resin

“…The 1 HNMR, 11 B NMR, and 31 P NMR of DTPA and AZB were recorded using a Bruker AVANCE AV II-400 NMR instrument, and using DMSO-d 6 as a solvent.…”

“…It is well known that 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives display superior flame retardant properties as consequence of activity in both the gaseous and condensed phases. [11][12][13][14] Many DOPO-based flame retardants with excellent flammability inhibiting properties have been reported. [15][16][17][18][19][20] A flame retardant derived from DOPO and triazole has been prepared.…”

Transparent low‐flammability epoxy resins with improved mechanical properties using tryptamine‐based DOPO derivative

“…The drawback of EP/7.5APP/ 2.5BPOPA thermoset was its lack of transparency. Other low‐flammability EPs also showed low transparency or no transparency, for example, chitosan‐based DOPO derivatives synthesized by Liu et al and pyrazine‐based DOPO derivative synthesized by Tang et al . The utilization of these materials would be limited by their lacks of transparency and aesthetics .…”