Water-soluble polyphosphazenes and their hydrogels

The development of methods for the incorporation of different side groups into polymers is a key step in the generation of specific combinations of properties. Two general methods exist for bringing about variations in polymer side groups: (1) The polymerization of different monomers that bear different side groups, and (2) macromolecular substitution reactions in which side groups already attached to a polymer are replaced by other units. The first method is more widely used than the second, mainly because organic macromolecular side group reactions are often relatively inefficient. Polyphosphazenes are unusual polymers in many ways. But their most significant advantage is the ease with which specific side groups can be linked to the phosphorus-nitrogen backbone by highly efficient substitutive techniques. Thus, by using the synthesis manifold shown it is possible to vary the side group structure over a wide range. Note also that sequential or simultaneous cosubstitution can yield polymers with two or more different types of side groups per chain. This approach also allows the incorporation of side groups that generate water-solubility, hydrogel formation, or hydrophilic surface character. This talk will illustrate these principles at work.