Inorganic backbone polymers

In many respects, the polyphosphazenes are the prototype inorganic backbone polymers, that exemplify the principles of ring-opening and condensation polymerization, macromolecular substitution reactions and their potential for molecular design, and an enormous range of derivatives with the same backbone but different organic side groups. 

Figure 3. Some examples of inorganic backbone polymers (R, and R2 may be organic).

Over the past two-and-a-half decades, efforts to develop new inorganic backbone polymers have steadily intensified. Two primary reasons account for this rising interest. First, materials requirements for advancing technologies have precipitated the need to look beyond primarily carbon-based polymers. Second, unique characteristics of the commercially successful poly(siloxanes) and the tremendous versatility and significant commercial potential of the poly(phosphazenes) have heightened awareness of the potential of inorganic polymers as sources for new materials. 

This is also a further example of a spiro-polymer as well as being of the inorganic backbone type. 

Silicones are probably best known for their application as sealants and as release materials for pressure sensitive adhesives [107]. The silicone polymer combines an inorganic backbone made from silicon-oxygen bonds with organic substitution on the silicon atom. This repeating unit, shown below is called a siloxane. 

Poly(phosphazenes) are similar, partly inorganic polymers in that they consist of inorganic backbone, in this case of nitrogen and phosphorus atoms. They are separated formally by alternating single and double bonds and carry organic groups on the phosphorus atoms (10.3). 

In fact, considering the basic structure of these materials (vide supra), it can be immediately realized that the basic features of poly(organophosphazenes) are the result of two main contributions. The first one is fixed and is basically related to the intrinsic properties of the -P=N- inorganic backbone, while the second is variable and mostly connected to the chemical and physical characteristics of the phosphorus substituent groups. Skeletal properties in phos-phazene macromolecules intrinsically due to the polymer chain are briefly summarized below. 

The biomedical uses of polyphosphazenes mentioned earlier involve chemistry that could in principle be carried out on a classical petrochemical-based polymer. However, in their bioerosion reactions, polyphosphazenes display a uniqueness that sets them apart. This uniqueness stems from the presence of the inorganic backbone, which in the presence of appropriate side groups is capable of undergoing facile hydrolysis to phosphate and ammonia. Phosphate can be metabolized, and ammonia is excreted. If the side groups released in this process are also metabolizable or excretable, the polymer can be eroded under hydrolytic conditions without the danger of a toxic response. Thus, poljnners of this tjT are candidates for use as erodible biostructural materials or sutures, or as matrices for the controlled delivery of drugs. Four examples will be given to illustrate the opportunities that exist. 

Electrochemistry of a Conductive Organic Polymer with an Inorganic Backbone... 

The primary approach to the development of main group inorganic polymer chemistry has been in the preparation, characterization and utilization of polymers with an inorganic backbone which may, or may not, be protected by organic substituents (la). Important members of this class of materials which are discussed in this volume and elsewhere include ... 

Andrianov, K. A. Polymers with Inorganic Backbones, Moscow, ANSSSR 1962, (Rqss.)... 

Radiation grafting can be performed with the monomers being neat or dissolved. In some cases, the use of solvents can produce graft copolymers with unique properties. Solvents, which wet and swell the backbone polymers, often assist grafting. Certain additives, including mineral acids and inorganic salts such as lithium perchlorate, as well as monomers such as divinyl benzene (DVB) and trimethylolpro-pane triacrylate (TMPTA), improve grafting yields.237... 

The use of polyamide solutions for the preparation of graft copolymers is restricted to monomer and initiator systems able to be dissolved and stand strongly polar media such as phenols, organic or inorganic strong adds, or aqueous salt solutions, which are common solvents for the backbone polymer. 

Allcock. H.R. Polyphosphazenes New Polymers with Inorganic Backbone Atoms, Science, 193, 1214-1219 (1976). 

Andrianov KA (1962) Polymers with inorganic backbones. Ac.Sci. Moscow, pp 106-184, 202-236 [in Russian]... 

Andrianov K.A., Polymers With Inorganic Backbones of Macromolecules, Moscow, Izd AN SSSR, 1962, p. 144. (Rus)... 

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