Polymers containing cyclophosphazene rings

One of the recent methods that has been applied for preparing polymers containing cyclophosphazene rings as pendant groups is by ring-opening metathesis polymerization (ROMP). The principles involved in the application of this strategy to cyclophosphazene monomers are as follows. 

An organic polymer containing a cyclophosphazene ring as a pendant group... 

There are many other polymers that are related to the polyphosphazene family. Thus, there are polymers which are actually made up of an organic backbone but contain a cyclophosphazene ring as a pendant group appended in their side chain. Other polymers that are related to polyphosphazenes are those that contain a third hetero atom in the backbone. Examples of such polymers are shown in Fig. 3.2. 

Polymer 2 (Fig. 4.1) is an example of a condensation polymer where a difionctional cyclophosphazene can react with an organic or an inorganic difiinctional reagent to afford a linear polymer. These polymers contain the cyclophosphazene ring as a repeat motif in the polymer backbone. These polymers have also been termed cyclolinear polymers. In this type of polymers also, the scope for variation is considerable, although in practice this has not been realized. Polymers of the type 3 (Fig. 4.1) are examples of in-termolecularly crosslinked cyclophosphazenes. These are reminiscent of thermoset polymers such as phenol-formaldehyde or melamine-formaldehyde resins. The presence of the cyclophosphazene units in the crosslinked matrix is expected to impart special properties. However, this family of polymers also has not yet fulfilled the promise that they seem to hold. 

Most of the polymers that contain cyclophosphazenes as pendant groups are prepared by polymerizing cyclophosphazene containing vinyl monomers. The vinyl group is attached to the cyclophosphazene ring either directly or through a spacer group. Recently, alternative procedures are also... 

There have been few important advances in this area during the past year. The first crystal structure of a phosph(m)azene, Bu (Me3Si)NP=NBu, has been reported, and the claim made last year, of the formation of a compound containing a phos-phazene linkage which forms part of a four-membered ring, has been shown to be erroneous. The formation and properties of cyclophosphazenes (mainly amino-derivatives) and the phosphazene polymers have been reviewed. The patent literature is the most important growth area, particularly where flameproofing applications are concerned. 

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