Surface Reactions of Polyphosphazenes

Some polymers have a specific set of bulk properties that make them ideal for a certain application, but cannot be used because the surface properties are inappropriate. For example, a material may have excellent elasticity but cannot be used in cardiovascular devices because the polymer surface triggers blood clotting. Alternatively, another polymer may have excellent surface biological compatibility but is too brittle for a cardiovascular application. An answer to this problem, like many others, is to select a polymer for its advantageous bulk properties and then carry out property modification reactions on the polymer surface without affecting the bulk material. 

Poly(organophosphazenes) are particularly suited for surface reaction chemistry because a wide variety of primary organic side groups can be utilized, and these can be subjected to a variety or organic transformations. It is also useful that the polymer backbone in most 

Note that many of these surface reactions involve the conversion of a hydrophophic polymer to one with a hydrophilic surface or vice versa. For example, the replacement of trifluoroethoxy groups at the interface by hydroxyl units changes a non-adhesive, highly hydrophobic surface to an adhesive hydrophilic one. Variations in the reaction conditions allow both the depth of transformation and the ratios of the initial to the new surface groups to be controlled. A possible complication that needs to be kept in mind for all of these surface transformations is that polymer molecular motions may bury the newly introduced functional units if the polymer comes into contact with certain media. For example, a hydrophilic surface on a hydrophobic polymer may become buried when that surface is exposed to dry air or a hydrophobic liquid. But this process can be reversed by exposure to a hydrophilic liquid. 

5 Hybrid Systems through Block, Comb, or Ring-Linked Copolymers 

Methods are now available for the hybridization of phosphazenes with other polymer systems in order to combine the special properties of the inorganic macromolecules with those of 

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