Cage–ladder‐structure, phosphorus‐containing polyhedral oligomeric silsesquinoxanes as promising reactive‐type flame retardants for epoxy resin

Abstract

We synthesized a novel cage-ladder-structure, phosphorus-containing polyhedral oligomeric silsesquinoxane (CLEP-DOPO-POSS) via the hydrolytic condensation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-vinyl trimethoxysilane (VTMS) with 2-(3,4-epoxycyclohexyl) ethyl trimethoxysilane and then incorporated it into epoxy resins (EPs) in different ratios with thermal curing technology. The structure of CLEP-DOPO-POSS was confirmed by Fourier transform infrared spectroscopy, NMR spectroscopy ( 1 H-NMR and 29 Si-NMR), matrix-assisted laser desorption ionization time-of-flight, and X-ray diffraction. The thermal stability, mechanical properties and flame retardancy effect of CLEP-DOPO-POSS on EP were comprehensively evaluated via thermogravimetric analysis (TGA), dynamic mechanical analysis, universal tensile testing, limiting oxygen index (LOI) measurement, UL-94 testing, and cone calorimetry. The flame-retardant mechanism of the EP modified with CLEP-DOPO-POSS was investigated by TGA-IR, TGA-mass spectrometry, and scanning electron microscopy. The experimental results show that CLEP-DOPO-POSS was homogeneously dispersed in the EP matrix. The LOI value reached 31.9, and the UL-94 grade passed V-0 with the presence of only 0.28% P (2.91 phr CLEP-DOPO-POSS). In addition, the EP composite containing CLEP-DOPO-POSS exhibited a better thermal stability and mechanical properties. The flameretardant mechanism was attributed to the quenching effect of the phosphorus-containing free radicals and the formation of phosphorusand silicon-containing char layers in the condensed phase.

A facile approach to prepare cage‐ladder‐structure phosphorus‐containing amino‐functionalized POSS for enhancing flame retardancy of epoxy resins

“…When the content of CLNH 2 -POSS increased from 5 to 7 wt%, T g,tan δ slightly decreased, which may have been due to the greater steric hindrance of the aggregated CLNH 2 -POSS hampering the curing of EP. 15,38 The thermal stability of the samples was systematically investigated by TG analysis under nitrogen atmosphere, the TGA and DTG curves are shown in Figure 10 (a,b), and the results are summarized in Table 5. It can be observed that the T 5% temperature and T max of CLNH 2 -POSS are 242.1 and 473.4 C, respectively, and its char residues at 800 C is 32.8%.The characteristic temperatures of CLNH 2 -POSS are comparable to those of the T A B L E 5 DMA, DSC, and TGA data of CLNH 2 -POSS and EP composites Samples…”

“…39 Besides, the char residues of CLNH 2 -POSS at 800 C increased 37.0% compared with that of CLEP-DOPO-POSS. 15 There is only one-step decomposition for all the EP composites.…”

“…Similar phenomenon has also been reported in epoxy resin modified with CLEP-DOPO-POSS. 15 The morphology of char layers after LOI testing was further investigated by SEM, and the SEM images of EP-0 and EP-3 are shown in Figure 15. Figure 15(a 1 ,a 2 ) show the exterior char layer morphology of EP-0, it can be seen that the exterior char layer of EP-0 presented a loose and discontinuous grain-like structure with some small crevassed and holes.…”

“…The CLEP-DOPO-POSS/EP composites exhibited good flame retardancy due to the good dispersion of CLEP-DOPO-POSS and phosphorus-silicon synergism. 15 Compared to epoxy group, KH540 is an alkoxysilane with aminopropyl group. Through hydrolytic condensation, amino groups could be introduced into the molecular structure of POSS, the reactive amino group of POSS could not only react with the epoxy groups, the reactive amino group would also endow POSS the potential to act as reactive FRs in the flame retardation of polyamide, polyurethane, and polyurea.…”

Synthesis of a novel phosphate‐containing highly transparent PMMA copolymer with enhanced thermal and flame retardant properties

“…Rao et al synthesized a novel liquid phosphorus‐containing polyol and prepared flexible polyurethane foams, which not only improved the flame retardancy of resins but also enhanced their thermal stability. Many other examples illustrate that reactive flame retardants can improve the thermal stability and flame retardancy of the matrix …”