Phosphazene cyclomatrix network polymers: Some aspects of the synthesis, characterization, and flame‐retardant mechanisms of polymer

Abstract

Novel phosphazene cyclomatrix network polymers were synthesized via nucleophilic displacement of activated nitro groups of tri(4-nitrophenoxy)tri(phenoxy)cyclotriphosphazene and hexa(p-nitrophenoxy)cyclotriphosphazene with the hydroxyls of bisphenol A. Both the monomers and polymers were characterized by Fourier transform infrared (FTIR) and 1 H-NMR spectroscopy, and their structures were identified. The thermal and flame-retardant properties of the polymers were investigated with thermogravimetric analysis in air, pyrolysis, and combustion experiments. Both solid and gaseous degradation products were collected in a pyrolysis process and analyzed with FTIR spectroscopy, gas chromatography/mass spectrometry, and scanning electron microscopy. The results demonstrated that the cyclomatrix phosphazene polymer would have excellent thermal stability and flame-retardant properties if it could form a crosslinked phosphorous oxynitride structure during pyrolysis or combustion. A flame-retardant mechanism of "intumescent" was proposed to elucidate the pyrolysis and combustion process.

Synthesis, characterization, thermal properties and flame retardancy of a novel nonflammable phosphazene-based epoxy resin

“…There have been many proposals for the flame-retardant mechanisms of the phosphazene-based polymers, such as the gas phase mechanism [21], the condensed phase mechanism [22], and the phosphorus-nitrogen synergism mechanism [23]. On the basis of the investigation on the thermal decomposition and flame retardancy of phosphazene-based epoxy resin in this article, the flame retardancy of the phosphazene-based polymers results from not a sole mechanism but comprehensive effects including: (1) the cyclotriphosphazene moieties can produce phosphoric acid or metaphosphoric acid during pyrolysis, which acts in the condensed phase promoting char formation on the surface as a barrier to inhibit gaseous products from diffusing to the flame and to shield the polymer surface from heat and air; (2) the cyclotriphosphazene moieties can release the inflammable gases such as CO 2 , NH 3 and N 2 during burning to dilute the hot atmosphere and cool the pyrolysis zone at the combustion surface; (3) these mentioned inflammable gases can cut off the supply of oxygen; (4) the cyclotriphosphazene moieties can also produce the phosphinylidyne free radicals (PO ), which can annihilate H and OH free radicals so as to terminate the combustion reaction [37]. However, the chemical transformations of the cyclotriphosphazene moieties and their participation in all stages of the combustion process for the phosphazene-based polymers are not yet fully understood, and a further intensive study is still necessary to clarify the flameretardant mechanisms of the phosphazene-based polymers.…”

Synthesis of tris(phenoxy)trifluorocyclotriphosphazenes and study of its effects on the flammable, thermal, optical, and mechanical properties of bisphenol-A polycarbonate

“…Among these additives, phosphazenes with an alternating P-N backbone not only have a wide range of thermal and chemical stabilities [7,8], but also provide thermal and flame-retardant properties to reinforce polymers and composites [9,10] that have attracted widespread attention [11,12]. In the condensed phase, the phosphorusbased flame retardants are particularly effective on polymers containing oxygen [13,14].…”

Syntheses and Characterization of Four Phosphaphenanthrene and Phosphazene-based Flame Retardants

“…6,7 There has also been great interest from the flame retardant community regarding phosphorus containing molecules (e.g., 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) for epoxy) and nitrogen-phosphorus containing molecules (e.g., Hexa-chloro-cyclotriphosphazene (HCCP) for epoxy, PLA, polybenzoxazines) as environmentally friendly alternatives to the existing, and often used, harmful halogenated flame retardants. [8][9][10][11][12] However, the above-mentioned reactive DOPO, phosphazene compounds and their derivatives could only be introduced to thermosets mainly through chemical reaction, which has restricted their application in many cases. [15][16][17] In this paper, the versatile Atherton-Todd reaction and the Kabachnik-Fields reaction were used to obtain novel derivatives containing phosphaphenanthrene and cyclotriphosphazene double functional groups which can be used as intumescent flame retardant additives.…”