Aryloxy Side Groups

Second, as a logical development of the first approach, polyphosphazenes have been synthesized that bear phosphine units connected to aryloxy side groups (37). The phosphine units bind organometallic compounds, such as those of iron, cobalt, osmium, or ruthenium (38). In several cases, the catalytic activity of the metal is retained in the macromolecular system (39). A similar binding of transition metals has been accomplished through nido carboranyl units linked to a polyphosphazene chain (40). 

Conversely, if the polymer could be made by some other route (for example, by macromolecular substitution), it might be stable at moderate temperatures where the rate of depolymerization is very slow, but would depolymerize to the cyclic trimer or tetramer when heated to higher temperatures. In fact, this behavior is found for uncross-linked polymers such as [NP(OPh)2] , that appear to be kinetically stabilized at moderate temperatures, but are sufficiently destabilized thermodynamically by the bulky aryloxy side groups that they depolymerize when heated above 150-200 °C. 

Commercial development of polyphosphazenes began with the production of high performance elastomers with fluoroalkoxy or aryloxy side groups. Other polyphosphazenes are used in medical devices.36 Another development is the use of... 

Other Direct Functionalization Reactions. In addition to the above processes, other direct functionalization reactions at the molecular level include the addition of organosilicon hydrides to allyl groups at the terminus of aryloxy side groups (56), the free-radical grafting of epoxy-, organosilyl-, or pyridine-bearing vinyl compounds to p-methylphenoxy side units (57), the quatemization of pendent tertiary amino groups, and... 

It should be noted that oils derived from the cyclic trimeric phosphazene 2 with fluorinated aryloxy side groups have been used as disk drive lubricants, partly because of their high levels of hydrophobicity, and liquids with similar structures but with fluoroalkoxy and aryloxy substituents have been developed as high performance hydraulic fluids for similar reasons. 

Polyphosphazenes that bear -D-glucosyl side groups cosubstituted with methyl-amine, alkoxy or aryloxy side groups have been symthesized (Allcock et al, 1991) (Figure 22) resulting in a range of polymers with varying water solubility, hydrophilic-ity or hydrophobicity. 

Another example of a non degradable pendant chain system involves the chemical linkage of catecholamines, such as dopamine, to amino-aryloxy side groups by diazo-coupling techniques (Allcock et al, 1983) (Figure 26). 

Figure 28 Structure of polyphosphazenes with fluoroalkoxy or aryloxy side groups.

The advantage of this synthesis protocol is the freedom to time the polymer composition and properties by varying the initial aryloxy side group ration, the degree of lithiation, and the amount of ester hydrolysis. 

Polyphosphazenes may provide particular advantages over their organic counterparts in the field of biomedical applications. For artificial organ research, materials can be synthesized that have specific surface properties, extreme stability under hydrolytic or oxidative conditions, and minimal interactions with blood or living tissues. Polymers that possess fluoroalkoxy or aryloxy side groups... 

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