Polyphosphazenes applications

Biomedical Applications. In the area of biomedical polymers and materials, two types of appHcations have been envisioned and explored. The first is the use of polyphosphazenes as bioinert materials for implantation in the body either as housing for medical devices or as stmctural materials for heart valves, artificial blood vessels, and catheters. A number of fluoroalkoxy-, aryloxy-, and arylamino-substituted polyphosphazenes have been tested by actual implantation ia rats and found to generate Httle tissue response (18). 

Applications. Polymers with small alkyl substituents, particularly (13), are ideal candidates for elastomer formulation because of quite low temperature flexibiUty, hydrolytic and chemical stabiUty, and high temperature stabiUty. The abiUty to readily incorporate other substituents (ia addition to methyl), particularly vinyl groups, should provide for conventional cure sites. In light of the biocompatibiUty of polysdoxanes and P—O- and P—N-substituted polyphosphazenes, poly(alkyl/arylphosphazenes) are also likely to be biocompatible polymers. Therefore, biomedical appHcations can also be envisaged for (3). A third potential appHcation is ia the area of soHd-state batteries. The first steps toward ionic conductivity have been observed with polymers (13) and (15) using lithium and silver salts (78). 

Whilst exhibiting the excellent low-temperature flexibility (with a Tg of about -80°C) and very good heat resistance (up to 200°C) typical of a silicone rubber, the fluorosilicones also exhibit good aliphatic oil resistance and excellent aging resistance. However, for some applications they have recently encountered a challenge from the polyphosphazenes (see Section 13.10). 

Applications. Many applications have been proposed for polyphosphazenes, particularly the non-cyclic polymers of high molecular weight, but those with the most desirable properties are extremely expensive and costs will have to drop considerably before they gain widespread use (cf. silicones, p. 365). The cheapest compounds are the chloro series... 

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.

Potin P and Jaeger RD. Polyphosphazenes Synthesis, structures, properties, applications. Eur Polym J, 1991, 415, 341-348. 

Allcock HR. Chemistry and Applications of Polyphosphazenes. Hoboken, NJ Wiley-Interscience, 2003, p. 504. 

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-... 

A new series of properties are expected for polyphosphazenes when the percentage of inorganic elements inherently present in the -P=N- skeleton is artificially enhanced by introducing fluorinated alcohols as side phosphorus substituents. This facilitates their application in different fields. 

In conclusion, polyphosphazenes containing fluoroalkoxy groups as side phosphorus substituents constitute one of the most relevant class of macromolecules of this family and have attracted remarkable interest in the past because of their outstanding properties and wide range of applicability, especially in low and high temperature domains, and have received renewed interest in more recent times [399,457]. 

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 this section we will describe the general principles that determined the biological applications of polyphosphazenes in different domains, putting an effort into establishing their specific utilization on the basis of structure-property relationships. This argument has been covered by several different review articles in the past [400-406,626] and has been recently highlighted by H. R. Allcock [627] and E. Schacht [407]. 

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. 

Allcock HR (2002) Chemistry and applications of polyphosphazenes. Wiley Interscience, Hoboken, New Jersey... 

All cock HR (2002) Chemistry and applications of polyphosphazenes. Wiley Interscience, Hoboken, New Jersey, p 690, Appendix 2, Table II.A Cowie JMG, Sadaghianizadeh K (1988) Polym Commun 29 126 Cowie JMG, Sadaghianizadeh N (1988) Makromol Chem, Rapid Commun 9 387 Allcock HR, Olmeijer DL, O Connor JM (1998) Macromolecules 31 753... 

Unique combinations of properties continue to be discovered in inorganic and organometallic macromolecules and serve to continue a high level of interest with regard to potential applications. Thus, Allcock describes his collaborative work with Shriver (p. 250) that led to ionically conducting polyphosphazene/salt complexes with the highest ambient temperature ionic conductivities known for polymer/salt electrolytes. Electronic conductivity is found via the partial oxidation of unusual phthalocyanine siloxanes (Marks, p. 224) which contain six-coordinate rather than the usual four-coordinate Si. 

Polyphosphazenes comprise some of the most intensively studied inorganic macromolecules. They include one of the oldest known synthetic polymers and many of the newest. In molecular structural versatility, they surpass all other inorganic polymer systems (with over 300 different species now known), and their uses and developing applications are as broad as in many areas of organic polymer chemistry. 

The development of synthetic routes to new polyphosphazene structures began in the mid 1960 s (2-4). The initial exploratory development of this field has now been followed by a rapid expansion of synthesis research, characterization, and applications-oriented work. The information shown in Figure 3 illustrates the sequence of development of synthetic pathways to polyphosphazenes. It seems clear that this field has grown into a major area of polymer chemistry and that polyphosphazenes, as well as other inorganic macromolecules, will be used increasingly in practical applications where their unique properties allow the solution of difficult engineering and biomedical problems. 

The study of open-chain polyphosphazenes has attracted Increasing attention In recent years, both from the standpoint of fundamental research and technological development. The polyphosphazenes are long chains of alternating phosphorus-nitrogen atoms with two substituents attached to phosphorus. These polymers have been the subject of several recent reviews (1-3). Interest has stemmed from the continuing search for polymers with improved properties for existing applications as well as for new polymers with novel properties. 

Today commercial applications for polyphosphazene specialty elastomers exist In aerospace, marine, oil exploration and Industrial fields. This paper describes the properties and applications for this unique class of elastomers. 

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