Phosphazene properties flame retardancy

Another valuable characteristic of many phosphazene polymers is their flame-retardant behavior and low smoke generation on combustion (13). This property is utilized in commercial appHcations. 

Abstract In this paper the synthesis, properties and applications of poly(organophos-phazenes) have been highlighted. Five different classes of macromolecules have been described, i.e. phosphazene fluoroelastomers, aryloxy-substituted polymeric flame-retardants, alkoxy-substituted phosphazene electric conductors, biomaterials and photo-inert and/or photo-active phosphazene derivatives. Perspectives of future developments in this field are briefly discussed. 

Fire retardancy is an often occurring theme in phosphazene chemistry and numerous reviews have focused on this subject over the years [ 10,44,387,393,396, 582]. In this article we will treat only aspects related to the flame-retardant properties of aryloxyphosphazene copolymers, which are the subject of the greatest number of applications. 

One of the most significant developments in phosphazene chemistry during the past year has been the reported application of alkoxycyclophos-phazenes, [NP(OR)2l3,4, as flame retardants in rayon. This development has, in turn, provided a stimulus for improvements to be made in the large-scale production of chlorocyclophosphazenes. Interest in the properties of the monophosphazenes has again increased considerably. 

In recent years, many poly(phosphazenes), [RoPN]n, with a variety of substituents at phosphorus have been prepared and they often exhibit useful properties including low temperature flexibility, resistance to chemical attack, flame retardancy, stability to UV radiation, and reasonably high thermal stability. (1,2) Compounds containing biologically, catalytically, or electrically active side groups are also being investigated. (3,4)... 

The phosphazene backbone also possesses unusual features that lead to a range of potential applications for these easily processed materials (Figure For example, it is extremely flexible and polyalkoxypho-sphazenes such as the -butoxy derivative [P(0"Bu)2=N] possess glass transition temperatures Tg of below -100 Furthermore, the P-N main chain is thermally and oxidatively stable, optically transparent from 220 nm to the near-infrared region and it imparts flame-retardant properties. 

Among inorganic heterocycles, perhalogenated cyclic phosphazenes occupy a very prominent place as the precursors for polyphosphazenes whose properties can he tuned by changing the substituents on the phosphorus sites (J). The heterocycles, as such, provide a robust framework for building a variety of novel molecules that have high thermal stability and flame retardancy, and have also been used recently to prepare a variety of dendrimers (2). The most widely studied among these are the perchlorinated cyclophosphazenes. Their syntheses reactions, properties, and application potential have been well documented a, 3-7). 

For halogen or alkoxy-substituted polymers Tg values are low (between -60 and —100° C). Alkoxy poly phosphazene with Ci - C3 substituents are elastomers. Higher alkoxy- or aryloxy-substituted polyphosphazenes are thermoplastics. Fluoroalkoxypolyphosphazenes exhibit a good stability toward diluted acids and bases. Some of them have outstanding thermal stability and good flame-retardant properties. 

In addition to certain of the articles cited above, numerous new applications of cyclophosphazenes have been described, almost exclusively in the patent literature. The ever popular flame retardancy property of phosphazenes is again an important area. The use of amidophosphazenes [(NH2)2PN] (n>3) for cellulose fibers is noted, - including an approach which allows the use of the amidophosphazene without previous removal of the difficult to separate NH Cf. Alkoxy (Et,Pr,Bu) phosphazenes combined with siloxanes have also been used in cellulosic fibers. Triallyl-phenoxytriphenoxycyclotriphosphazene is an additive in the production of flame retardant poly (siloxanes). ... 

Although the polyhalophosphazenes have potentially useful physical and mechanical properties, their chemical reactivity and hydrolytic instability rule out their practical use. Luckily, however, an important aspect of the phosphazene polymer system is the relative ease with which the properties can be modified by the introduction of different side groups. Useful properties of such organopoly-phosphazenes include resistance to water, solvents, oils, and so on non-inflanunability and flame retardancy stability to visible and ultraviolet radiation high thermal stability (>200 C) and low-temperature flexibility and elasticity. 

In addition to the organic solvents described above, there are quite a few more organic compounds considered as solvent candidates for Li-ion battery electrolytes. In many cases, these molecules are more appropriate as additives instead of solvents due to the inferior physical and electrochemical properties of the resulting electrolyte if such molecules are used in high concentration. These molecules include the non-fluorinated and fluorinated varieties of alkyl sulfates [113], alkyl sulfites [21, 59, 63], alkyl phosphates [66], and phosphazenes [84]. Some of them have been employed as SEI formation additives or flame retardant additives and will be discussed in the respective sections of Chap. 9. 

Other studies on the flame retardant applications of phosphazene derivatives include the use of cyclotriphosphazenes to improve the flame-retardant properties of epojy composites,using fluorinated phosphazene derivatives as non-flammable electrolytes in lithium ion batteries and utilizing phosphazenes as flame-retardant additives in curing polysiloxanes. °... 

Since both miscible and immiscible phosphazene blends are of considerable interest as membrances, biomaterials, or flame retardant materials, it is worthwhile to study the compatibility of these kinds of blends in more detail in order to understand more about the interaction between the polymer pair and the stability of the blends. Our goal in this study is to prepare PCPP/PS blends and investigate the compatibility and tile properties of the blends by optical clarity, DSC, SEM, FTIR, TGA and LOI. PCPP/PS is chosen in this study because (a) PCPP is known to be flame retardant (5), (b) polystyrene is a well-known versatile organic polymer and has been selected to gi t or blend with phosphazene polymers in most of the polyphosphazene-organic polymer hybrids systems (14,15), and (c) the similarity of aromatic side groups in both of the polymers. In addition, since rcPP has a special thermotropic transition temperature, T(l), and in order to further understand tiie stability of the blends, the compatibility influenced by temperature is also studied before and after T(l) transition by DSC. 

The first phenomenon observed is the improved resistance of these materials to combustion, in a way that they may be classified as intrinsically self-extinguishing substrates. For instance, the LOI value for PTFEP is reported to be 48 [452], which is much higher than reported for classical organic plastics [283], while phosphazene fluoroelastomers have been considered as fire-retardant materials since the very beginning of their preparation and utilization [562]. Similarly to aryloxy- and arylamino- substituted POPs [389,390] (vide infra),it may be expected that the flame-resistance properties of phosphazene fluoroelastomers could be successively exported to stabihze organic macromolecules when blended with these materials. 

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