Polyphosphazene crosslinking

Fig. 10 Two methods of polyphosphazene crosslinking a using benzophenone and UV irradiation, and b via acid-base complexation with PBI...

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. 

Finally, a new water-soluble polyphosphazene was recently synthesized that has the structure shown in 36 (46). This polymer has two attributes as a biomedical macromolecule. First, the pendent carboxylic acid groups are potential sites for condensation reactions with amines, alcohols, phenols, or other carboxylic acid units to generate amide, ester, or anhydride links to polypeptides or bioactive small molecules. Second, polymer forms ionic crosslinks when brought into contact with di- or trivalent cations such as Ca or Ai3+. The crosslinking process converts the water-soluble polymer to a hydrogel, a process that can be reversed when the system... 

Allcock, H. R., Gebura, M., Kwon, S., and Neenan, T. X., Amphiphilic polyphosphazenes as membrane materials Influence of side group on radiation crosslinking, semipermeability, and surface morphology. Biomaterials. 19. 500, 1988. 

Among the various materials are crosslinked PAN, polyphosphazenes, polyphe-nylenesulfide, polyetheretherketone, and various polymer blends [28-31]. Particularly interesting is the use of zeolites as filler in organic polymers, which aims at improving the performance of (silicone-based) membranes for separations in nonpolar solvents, by adding more cross-links to the membrane material [32, 33]. 

Guo, Q. et al., Sulfonated and crosslinked polyphosphazene-based proton-exchange membranes, J. Membr. Sci., 154, 175, 1999. 

In general, polyphosphazenes are not very resilient to heating, but their thermal decomposition occurs with a high degree of crosslinking and the formation of a dense structure that acts as a flame retardant [3], For some copolymers, the presence of phosphazene sequences enhances the thermal stability. Some other literature reports regarding thermal decomposition of these compounds are given in Table 17.2.1. 

Studies of membranes based on polyphosphazenes, bearing groups other that substituted phenoxy groups, have been continued, in particular to develop materials for specific apphcations. Ion-exchange membranes of cross-linked and non-crosslinked sulfonated [NP(OC6H4Me-3)2]n have been... 

Diffusion coefficients for methanol (concentration range 1.0-5.0 M) in ion-exchange membranes of UV-crosslinked sulfonated poly(bis-3-methoxyphenoxyphosphazene) (134) have been reported to be much smaller than those in Nafion perfluorosulfonic ion-exchange membranes. Application of polyphosphazene-based membranes in methanol-based fuel cells has been reported. ... 

A wide- and small angle X-ray diffraction study of crosslinked (134) has shown the presence of two phases, viz. an amorphous phase and a two-dimensional ordered phase. Changes of the ordered structure depend on the ion-exchange capacity of the polymer and extent of water swelling. Pervaporation membranes have been prepared by thermally crosslinking of polyphosphazenes bearing p-methoxyphenoxy, methoxyethoxyethoxy and o-allylphenoxy groups in the presence of a radical initiator. ... 

These depolymerization reactions are complicated by side reactions. For example, if both P—Cl and P—OCH2CF3 or P—OCgHj units are present in the same reaction system, thermolysis causes elimination of CF3CH2CI or C5H5CI with simultaneous crosslinking of the chains . Clearly, depolymerization and elimination reactions are important in the context of the practical thermal stability of polyphosphazenes. Thus,... 

A decline in catalytic activity with use was detected for reactions catalyzed by either species. Polymers 2 and 7 in the absence of cobalt both revealed excellent stability at 190 C (hydroformylation temperatures). This is illustrated by the TGA curves shown in Figure 4. Curve A shows an onset of decomposition for phosphinated polyphosphazene of 400 C, slightly better than that of phosphinated polystyrene (curve B, 20Z crosslinked curve C, 2Z crosslinked). Loss of phosphorus was observed over a period of 45 hours for a catalyst derived from 2 (2Z DVB crosslinked). The data depicted in Figure 5 reveal benzene, toluene, benzyl alcohol, diphenylphosphine and triphenyl phosphine as cleavage products. If one recalls the previously discussed homogeneous results it should be clear that the PPho is derived from a phosphide intermediate such as 8. ... 

Copolymers containing the isoelectronic Si-0 backbone grafted to the P-N backbone were obtained by using the polyphosphazene anion to open the ring in hexamethylcyclotrisiloxane (23, 24). To avoid crosslinking reactions, a THF solution of the polymer anion at -78 0 was treated with [Me2SiO]3 and the resulting mixture was warmed to room temperature and stirred for two hours. 

Polyphosphazene sulfonic acids [200, 201] offer a unique combination of inorganic backbone with high stability, high ionic density and structural diversity with crosslinking alternatives. Polyphosphazenes with sulfonamide functionalization have been reported with high proton conductivity [202]. 

Q. Guo, P.N. PiNTAURO, H. Tang, S. O Connor, Sulfonated and crosslinked polyphosphazene-based proton-ex-change membranes. Journal of Membrane Science 154 (1999) 175. 

As already reflected by the number of review papers, the interest in biomedical applications of polyphosphazenes continues to grow. The biodegradable polymer NP(NHC6H4C02H-4)i.8(NHC6H4C02H-4)o.2 n has been prepared and fully characterized. The carboxylato groups can react with Ca -ions to form crosslinks and to convert the water-soluble polymer to a hydrogel. Controlled drug release experiments have been carried out for chitosan en-... 

Polyphosphazene elastomers undergo crosslinking when 7-irradiation is performed in a vacuum. The yield of cross-Unking, G(X), varies from about 1 to 12 depending on the percentage of allyl groups in the polymer chain [68]. 

Fig. 3.47. Chemical crosslinking of polyphosphazenes with glucosyl side-groups...

Boston, Ma., March 1999, p.355-6. 012 lONICALLY CROSSLINKED POLYPHOSPHAZENE MICROSPHERES Andrianov A K Chen L Sule S S Avant Immunotherapeutics Inc. 

---