Polyphosphazenes structure-property relationships

The general structure of polyphosphazenes substituted with fluorinated alcohols is described by the Formula below while the basic structure-property relationships for these substrates are collected in Table 9. 

In this section we will describe the general principles that determined the biological applications of polyphosphazenes in different domains, putting an effort into establishing their specific utilization on the basis of structure-property relationships. This argument has been covered by several different review articles in the past [400-406,626] and has been recently highlighted by H. R. Allcock [627] and E. Schacht [407]. 

TABLE 1 Summary of Side Group Structure-Property Relationships in Polyphosphazenes... 

In the rest of this chapter an attempt will be made to describe how this field developed, how polyphosphazenes are synthesized, how the system provides almost unprecedented opportunities for the design of new macromolecules, and how the molecular structure-property relationships have been developed to produce a wide range of advanced materials. 

Enough is now known about the effect of different side groups attached to a polyphosphazene chain to allow some general structure-property relationships to be understood. To a limited extent, these relationships allow the prediction of the properties of polymers not yet synthesized. Some general relationships will be described in the following sections, but specific properties associated with certain side groups are summarized in Table 3.1. 

Recent studies have extended the structure-property relationships in polyphosphazenes to include polymers that show interesting electrical or optical behavior in the solid state. These fall into three categories - (1) polymers that are good solid solvents for salts and which function as solid ionic conductors, (2) species that bear electronically active side groups, and (3) polymers that bear rigid organic units that generate liquid crystalline or non-linear-optical behavior. 

Understanding the relationship between molecular structure and materials piroperties or biological activity is one of the most important facets of biomaterials synthesis and new-drug design. This is especially true for polyphosphazenes, where the molecular structure and properties can be varied so widely by small modifications to the substitutive method of synthesis. 

Table 1 is a summary of current knowledge of the relationship between side group structure in polyphosphazenes and biomedically important properties. Within rather broad limits two or more of these properties can be incorporated into the same polymer by a combination of different side groups attached to the same macromolecular chain. 

Moreover, the molecular structural, synthetic, and property nuances of these polymers illustrate many of the attributes, problems, and peculiarities of other inorganic macromolecular systems. Thus, they provide a "case study" for an understanding of what may lie ahead for other systems now being probed at the exploratory level. In short, an understanding of polyphosphazene chemistry forms the basis for an appreciation of a wide variety of related, inorganic-based macromolecular systems and of the relationship between inorganic polymer chemistry and the related fields of organic polymers, ceramic science, and metals. 

The synthesis of a large number of polyphosphazenes and an investigation of their properties has provided an almost unique opportunity to understand the relationship between the structure and properties in these systemsT A long-range objective is to be able to predict the properties of yet-unsynthesized polymers. 

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