Phosphazenes applications

Diffusion of solutions of Cr, Co and Mn ions through a PTFE membrane allows for separation of Cr from the remaining ions. Thermal stability of polymeric materials is a significant consideration in many poly(phosphazene) applications. The kinetics of the thermal degradation of PTFE are best fit with a model requiring a two step initiation for depolymerization. These steps involve formation of defect units, such as =P(0)NH- and =P(0)N(CH2CFj)-, which become active centers for depolymerization. Mixed... 

Continued commercial interest in poly(phosphazenes) is demonstrated by extensive patent activity and related applications oriented publications (some of which have been noted above). Fire retardency is an ongoing theme in cyclo-and linear phosphazene applications (see section 3). Aryloxy phosphazenes, including a commercial product, Eypel A, have been utilized for components for fire resistance in foam cushioning, rocket motor insulation and electrical wire coating . Alkoxy phosphazene polymers and copolymers impart antistatic properties to silver halide based... 

Applications. Among the P—O- and P—N-substituted polymers, the fluoroalkoxy- and aryloxy-substituted polymers have so far shown the greatest commercial promise (14—16). Both poly[bis(2,2,2-trifluoroethoxy)phosphazene] [27290-40-0] and poly(diphenoxyphosphazene) [28212-48-8] are microcrystalline, thermoplastic polymers. However, when the substituent symmetry is dismpted with a randomly placed second substituent of different length, the polymers become amorphous and serve as good elastomers. Following initial development of the fluorophosphazene elastomers by the Firestone Tire and Rubber Co., both the fluoroalkoxy (EYPEL-F) and aryloxy (EYPEL-A) elastomers were manufactured by the Ethyl Corp. in the United States from the mid-1980s until 1993 (see ELASTOLffiRS,SYNTHETic-PHOSPHAZENEs). 

Figure 12.30 Potential uses of polyphosphazenes (a) A thin film of a poly(aminophosphazene) sueh materials are of interest for biomedical applications, (b) Fibres of poly[bis(trifluoroethoxy)phosphazene] these fibres are water-repellant, resistant to hydrolysis or strong sunlight, and do not burn, (c) Cotton cloth treated with a poly(fluoroalkoxyphosphazene) showing the water repellaney eonferred by the phosphazene. (d) Polyphosphazene elastomers are now being manufaetured for use in fuel lines, gaskets, O-rings, shock absorbers, and carburettor eomponents they are impervious to oils and fuels, do not bum, and remain flexible at very low temperatures. Photographs by eourtesy of H. R. Allcock (Pennsylvania State University) and the Firestone Tire and Rubber Company.

Among other uses, these polymers have been employed in a variety of biomedical applications. Poly(phosphazenes) containing organic side chains, derived from the anaesthetics procaine and benzocaine, have been used to prolong the anaesthetic effect of their precursor drugs. They have also been used as the bioerodable matrix for the controlled delivery of drugs. 

Allcock HR. Qrganometallic and bioactive phosphazenes. J Polym Sci Polym Symp, 1983, 70, 71-77. Allcock HR. Poly(organophosphazenes) Synthesis, unique properties and applications. Makromol Chem... 

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. 

To conclude this synthetic section, it appears very clear that the experimental approaches for preparation of POPs are very numerous and give accessibility to phosphazene polymers and copolymers with different structures and properties. Moreover, it has been recently estimated [10,383] that the total number of polyphosphazenes reported up to now in the literature is about 700, and that these materials can find potential practical application as flame- and fire-resistant polymers [44,283, 384-388] and additives [389, 390] thermally stable macromolecules [391] chemically inert compounds [392] low temper-... 

The general conclusion is that the phosphazene macromolecules synthesized and characterized up to now show a large range of properties and that they can potentially be exploited in many different applicative domains. 

S. H. Rose in 1968 [263, 265] first described the reaction of polydichloro-phosphazene with trifluoroethoxy groups coupled with a second fluorinated alkoxy residue of longer chain. During the successive twenty years they were deeply investigated by Horizon Inc. [263, 265, 502-506, 518, 544, 552-554], AMMRC [396, 452, 555-557], NASA [517, 522, 523], The Firestone Tire and Rubber [393,519,528,530,533,558,559], and Ethyl Co. [507,560,561] for the applications described above (vide supra). 

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. 

In conclusion, polymer electrolytes based on phosphazene backbone and containing ether side chains are, after complexation with alkali metal salts, among the highest ionically solvent-free polymer salt complexes, with conductivities in the order of 10" -10" S cm However, these conductivities are still below the value of 10 S cm" which is considered to be the minimum for practical applications. Therefore the design of new polyphosphazenes electrolytes with a higher conductivity and also a higher dimensional stability still remains a challenge for future researchers. 

In conclusion, all these types of light-induced reactions involving polyphosphazenes readily account for the great importance assumed by this topic in the phosphazene domain and for the remarkable application potentials of especially designed phosphazene materials. 

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. 

The use of n-butylamino-derivatives of cyclophosphazenes in flame-proofing cellulose-based fabrics has been described in a patent application. The topic of fiame retardants is also covered in a recent review, where phosphazenes are important because of their relatively high phosphorus and nitrogen contents. 

The hydrido phosphazenes 27 themselves are quite valuable reagents and can be converted into halogenocyclophosphazenes upon treatment with chlorine, bromine, or iodine. The elusive cyclophosphazenes containing a P I bond have been synthesized in this manner (43). Another application of the hydrido phosphazenes is their deprotonation, leading to phosphazene anions, which provide a valuable route for other P-C compounds (161). The phosphazene anions can also be generated by the cleavage of the bicyclophosphazenes 25 with LiBEt3H (163). 

A few applications of acyclic phosphazenes have been mentioned. 

A review of the applications of Htlckel molecular orbital theory to various aspects of phosphazene chemistry, including... 

Thus, important structure/property relationships are emerging that are relevant to electronic and optical materials applications for these materials. In a different vein, side chain crystallization has resulted in the first liquid crystalline inorganic and organometallic macromolecules, viz., unusual poly(dialkoxy-phosphazenes) described by Allcock (p. 250) and Singler (p. 268). 

In the case of poly(alkoxyphosphazenes) (IV) or poly(aryloxyphos-phazenes) (V) a dramatic change in properties can arise by employing combinations of substituents. Polymers such as (NP CHjCF ) and (NP CgH,).) are semicrystalline thermoplastics (Table I). With the introduction of two or more substituents of sufficiently different size, elastomers are obtained (Figure 4). Another requirement for elastomeric behavior is that the substituents be randomly distributed along the P-N backbone. This principle was first demonstrated by Rose (9), and subsequent work in several industrial laboratories has led to the development of phosphazene elastomers of commercial interest. A phosphazene fluoroelastomer and a phosphazene elastomer with mixed aryloxy side chains are showing promise for military and commercial applications. These elastomers are the subject of another paper in this symposium (10). 

Other Applications. Thus far the phosphazene fluoroelastomers (PNF) and aryloxyphosphazene elastomers (APN) have moved to the commercial stage. In addition to elastomers, phosphazenes are being investigated as fluids, resins and plastics. Other areas which hold promise include fire resistant paints (55), fiber blends and additives, agrichemicals and herbicides, drug release agents and electrically conducting polymers (6). 

A big increase in the number of patent applications on this topic is apparent. The area has been reviewed,177-178 and it is clear that the alkoxycyclophosphazenes find the widest range of applications, particularly in improving the flame resistance of rayon179-188 and polyurethanes.189-191 Phenoxy-substituted phosphazenes have attracted less attention.192-194 Oligomeric chlorocyclophosphazenes also have... 

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. 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

Phosphazenes can be polymerized and in many instances their polymers have advantages over the carbon-based polyolefins and polyesters. 45 However, commercial application is not as well developed as for the silicones (R2SiO)JP, (see page 749). Early studies were hampered by the sensitivity of the phosphorus-chlorine bond to... 

Phosphazene polymers are inherently good electrical insulators unless side-group structures allow ionic conduction in the presence of salts. This insulating property forms the basis for applications as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

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 applications. 

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