Systems 6 Poly phosphazenes

Cyclophosphazenes are a fascinating group of inorganic heterocyclic compounds whose chemistry is multi-faceted, well developed and reasonably well understood. They are closely related to the linear poly-phosphazenes this relationship is unlike any other existing between ring-polymer systems. Although cyclic siloxanes and polysiloxanes have a close interrelationship, the number and types of cyclophospha-zene derivatives that are known, together with their exact counterparts in polyphosphazenes, underscore the utility of cyclophosphazenes as models for the more complex polyphosphazenes. The literature on cyclophosphazenes has appeared earlier in the form of books (1,2), chapters of books (3-5), authoritative compilations of data (6,7), and several reviews (8-21). The current literature on this subject is reported annually in the Specialist Periodic Reports published by the Royal Society of chemistry (22). This review deals mostly with chlorocyclo-... 

The inorganic poly(phosphazene) backbone has received attention as a PEM candidate. This is an attractive system for study due to its ease of synthesis and subsequent modification by many functional groups. However, these membranes generally show low glass transition temperatures and somewhat poor mechanical properties, and they require cross-linking to enhance their performance in hydrated environments. 

This section is concerned with polymers derived from open-chain phosphazenes, phospha(thia)zenes and related cross-linked materials. Cyclolinear and cyclomatrix materials as well as carbon-chain polymers with cyclophasphazene substituents are covered in Section 3. General and specific reviews have appeared including an overview of recent development in inorganic polymers including poly(phosphazenes), a comprehensive survey of hybrid siloxane-phosphazene systems, water-soluble phosphazenes and related hydrogels, a brief survey of polymerization reactions and mechanisms, and sulfur containing poly(phosphazenes). ... 

Information on the formation of poly(phosphazenes) from small molecule precursors continues to become available. New results in ring-opening polymerization are limited in mixed ring systems. The polymerization of the cabophosphazene, CfCNPcIjNPcI, occurs at relatively mild conditions and can be... 

Since the effect of the nature of the polymer backbone has not been studied extensively using well-defined polymers, it is worth summarizing the observations from less controlled systems based on comparisons of poly(phosphazene), poly(methylsiloxane), poly(vinyl ether), poly(acrylate), poly(me-thacrylate), poly(chloroacrylate), and polystyrene backbones [233-241]. In general, the mesogen is more decoupled from the polymer backbone as the latter s flexibility increases. This is because the dynamics of ordering increase with increasing flexibility, which increases the ability of the mesogenic side-chains to form more ordered... 

S.M. Ibim, et al.. In vitro release of colchicine using poly(phosphazenes) the development of dehvery systems for musculoskeletal use, Pharm. Dev. Technol. 3 (1) (1998) 55-62. 

The delocalization energy is obtained from the difference in the heats of combustion of the monomer and the corresponding monomeric unit of the polymer. In a few systems, such as cyclosiloxanes/poly(siloxanes) or phosphazenes/poly(phosphazenes), the delocalization energies are equal in monomer and polymer. If the monomer is resonance-stabilized and the polymer is not, for example, through absence of planarity, then the resonance energy becomes negative. In the polymerization of benzene to (—CH=CH—) , therefore, A// p will be positive, since is zero. 

A major foctor in the diversity of the pho hazene polymer system, and indeed the reason poly(phosphazenes) are unique among polymers, is the broad range of chemistry that can be carried out on the poly(pho9hazenes) once the backbone has been formed. As mentioned above, the best exanq>les of this are the siniple, yet very... 

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