Phosphonitrile Polymers

These polymers, also called polyphosphazenes, are useful materials when they are substituted with organic compounds [173]. They are prepared from hexachloro-cyclotriphosphazenes by ring opening polymerizations  

It is believed that the mechanism of polymerization involves an attack by electron-rich nitrogen of one cyclic monomer upon another one. At first, a cation forms through ionization of a phosphorus chloride bond [173]  

This is followed by an attack on another monomer molecule  

alkoxy, and aminocyclotriphosphazenes fail to polymerize. This is believed to be due to an absence of easily ionizable halogen to phosphorus bonds. At the same time, materials that presumably facilitate ionization of the phosphorus to halogen bonds, such as water, carboxylic acids, and metals, accelerate the polymerization [173]. 

Mixed fluoroalkoxy compounds can be used to obtain a variety of properties. The materials find application as elastomers, because they exhibit good chemical resistance and good thermal stability. In addition, many retain the useful elastomeric properties at low temperature. As a result, among other applications, they are attractive for use as sealants and as fuel lines in arctic environment. 

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Why would you predict that the chloro groups in phosphonitrilic polymers would be attacked by water ... 

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 ... 

Phospham or phosphonitrilic amide, PNNH, is a fascinating material also isoelectronic with Si02 [213], Its formula suggests a relationship to LiPN2 with the filled high cristobalite structure, but it is amorphous to X-ray analysis. Phospham has been used in the synthesis of phosphorus-containing nitrides [111], There is an extensive literature on phosphonitrile polymers (for a review, see [214]). 

Phosphonitrilic polymers are self-extinguishing or fire-retardant. This led to the development of flame- and heat-resistant polyimide composites that are prepared from maleimide-substituted phosphazenes. The maleimide group is used for crosslinking. The substituted phosphazene can be illustrated as follows ... 

C.D. Schmulbach, Phosphonitrilic polymers. Prog. Inorg. Chem., 4, 275, 1962. 

FIGURE 1 Schematic synthesis of derivatized phosphonitrilic polymers from (NPCljlj trimer. 

FIGURE 6 Effect of bond alternation and ligand electronegativity on the second hyper-polarizability of the phosphonitrilic polymer. 

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