Polyphosphazene foam

These are inorganic phosphorus polymers— that is, polymers with no carbon in the badcbone chain. The phosphonitrilic polymers, more exactly named polyphosphazenes, have the general formula  

Polyphosphazene compounds have been used in a variety of flame-retardant applications. The phosphazenes have great utUity as flame retardants because of (1) the high percentage of phosphorus present, (2) the simultaneous presence of large amounts of nitrogen, and (3) the possibUity of incorporation of halogens at the same time (10). 

A 1980 Naval Research Laboratory report provides data on the toxic combustion products evolved by burning polyphosphazene foams, with and without fire retardants. Toxicants produced were CO, CO2, 2-chlorobutane, 1-chlorobutane, benzene, toluene, and trichloroethylene (for foams not coated with fire-retardant paints) (11). 

In 1981 lieu et al at the University of Pittsburgh reported on studies comparing the flammability-toxicity of polyphosphazene and polyurethane foams, using the newly proposed Potential Hazard Index (PHI). In these studies polyphosphazene ranked less hazardous than polyurethane foams. Toxic gases evolved by polyphosphazene included CO, HCN, and NO2, with relative proportions dependant on which formulation was under study (12). 

Syntactic foams have been discussed in Chapter 2 on Thermosetting Foams. The discussion following is intended to cover points not made in Chapter 2. 

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MISCELLANEOUS AND SPECIALTY FOAMS (Epoxy Foams, Polyester Foams, Silicone Foams, Urea-Formaldehyde Foams, Polybenzimidazole, Foams, Polyimide Foams, Polyphosphazene Foams, and Syntactic Foams)... 

This specification, prepared by the Navy, covers polyphosphazene elastomeric foam material for thermal insulation on piping, in either sheet or tubing form. Polyphosphazene foam has excellent fire-retardant properties and is suitable for use in the range -20 to 180°F (-29 to 82.TC) in tubular form (Form T). Form S covers sheet form. 

Taylor, Naval Ship RAD Center, Annapolis, MD 1978, NASA TM-78523, N79-12029 Wldenor, W. M. "Polyphosphazene Foam Thermal Insulation" 1981, DTNSRDC TM-28-81-324. 

Aryloxyphosphazene copolymers can also confer fireproof properties to flammable materials when blended. Dieck [591] have used the copolymers III, and IV containing small amounts of reactive unsaturated groups to prepare blends with compatible organic polymers crosslinkable by the same mechanism which crosslinks the polyphosphazene, e.g. ethylene-propylene and butadiene-acrylonitrile copolymers, poly(vinyl chloride), unsaturated urethane rubber. These blends were used to prepare foams exhibiting excellent fire retardance and producing low smoke levels or no smoke when heated in an open flame. Oxygen index values of 27-56 were obtained. 

Widenor, W. M. "Model Fire Tests on Polyphosphazene Rubber and Polyvinylchloride (PVC)/Nitrile Rubber Foams"... 

Ratings of Some Polyphosphazene and Pol)mrethane Foams," Journal of Combustion Toxicology, 8 282-259 (November... 

Among tlie many patent claims for polyphosphazenes are various bioactive or biodegradable materials, foamed products, semi-permeable membranes and immobilised enzymes. Enzymes can be covalently linked to polyphosphazenes and the blood compatibility of heparin is improved by such treatment [92]. 

TE scaffolds made from polymers are available in different formats as already mentioned in Section 4.1. Polymeric scaffolds can be based on fibres, foams, membranes and 3D bulk materials, using simple linear polymers or crosslinking these, ending up with elastomeric or even thermoplastic structures. In general, the usage of polyphosphazenes should also allow the realisation of similar concepts. Nevertheless, in the literature only a relatively small number of examples are given for the fabrication of polyphosphazene-based scaffolds for TE [2-27]. 

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