Phosphazenes chemistry, review

Fire retardancy is an often occurring theme in phosphazene chemistry and numerous reviews have focused on this subject over the years [ 10,44,387,393,396, 582]. In this article we will treat only aspects related to the flame-retardant properties of aryloxyphosphazene copolymers, which are the subject of the greatest number of applications. 

A review of the applications of Htlckel molecular orbital theory to various aspects of phosphazene chemistry, including... 

Early comprehensive reviews of phosphazene chemistry by Audrieth, Steinman, and Toy (43), Gribova and Ban-Yuan (214), Paddock and Searle (337), Shaw, Fitzsimmons, and Smith (401), and Schmulbach (388) were followed by reviews on specific aspects, such as preparative methods (402), structure and bonding (336, 407), and high polymers (254). Some excellent books dealing with the chemistry of cyclophosphazenes (13, 21, 216) have also appeared. The recent reviews of Allcock (22), Sowerby (418), and Keat and Shaw (249) describe the developments up to 1970-1971. Several short articles on this topic have also appeared from time to time (264, 403, 404, 408). Phosphazene chemistry is now reviewed annually (251). 

Allen, C.W. (1994) Linear, cyclic, and pol3mieric phosphazenes. Coordination Chemistry Reviews, 130, 137-173 AUen, C.W. (1996) Phosphazenes. Organophosphorus Chemistry, 27, 308-351 Kondo, Y., Ueno, M. and Tanaka, Y. (2005) Organic synthesis using organic superbase. Journal of Synthetic Organic Chemistry, 63, 453 63. 

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 nomenclature and numbering system adopted in this article is the one currently widely used in the literature and corresponds closely to the one suggested by Shaw (13,17). Only the chemistry of chlorocyclo-phosphazenes is dealt with in this review. The structural and bonding aspects are not considered here. 

During the past 5 years considerable progress has occurred in the structural chemistry of phosphazenes, substitution reactions, reaction mechanisms, synthetic procedures, and phosphazene high polymers. In this review, a broad outline of cyclophosphazene chemistry will be presented with an emphasis on the most recent work. The chemistry of phosphazene high polymers has been reviewed comprehensively in recent years (21, 22, 24, 412), and this topic will be mentioned only briefly. Cyclophosphazanes (21, 216) and phosphorines containing skeletal heteroatoms other than nitrogen and phosphorus (21, 249) are outside the scope of this review. 

Step-by-step growth of phosphazene chains can be achieved and the five-phosphoms chain can be converted into a dendrimeric stmcture. The fascinating chemistry of dendrimeric phosphors nitrogen molecnlar architecture has been reviewed. ... 

The polymeric phosphazenes are treated in chapter (see Polyphosphazenes) A recent monograph covers the chemistry of polyphosphazenes (nomenclature, synthesis of cyclic monomers , ring opening polymerization, condensation polymerization, substitution, polymer properties, and applications more than 1000 literature citations). Other reviews have also been published recently. Sulfur-containing polyphosphazenes have also been described. ... 

Review papers on cyclic compounds with a phosphazene moiety have covered several areas, viz. metal complexes derived from organo-substituted, polymers with cyclotriphosphazene entities and chemistry of perfluorinated cyclo-phosphazenes. Azaphosphinines have been reviewed in the scope of the phosphorus-carbon heterocyclic chemistry. ... 

Recent developments in the polyphosphazene chemistry have been re-viewed. The role of polyphosphazenes as biodegradable polymers as hydrogels for tissue engineering and as induced helical polymers has been discussed. Preparation and application of poly(thionyl phosphazenes) are discussed in two review chapters. ... 

Interest continues to be shown in acyclic phosphazenes (phosphazo derivatives, phosphine imines, phosphoranimines). Reviews include a comprehensive survey of the chemistry (synthesis, structure, bonding and spectroscopy) of transition metal complexes of phosphoranimines, a survey of recent uses of Ph2P(=NSiMe3)NSiMej as a precursor to transition metal... 

Focused reviews of various aspects of cyclophosphazene chemistry including the relation of exocyclic substituents to polymerizability and synthetic transformations of organometallic and bioactive phosphazenes , a summary of variables involved in the synthesis of bicyclic phosphazenes... 

Reviews of cyclophosphazene chemistry have focused on several important subtopics rather than comprehensive surveys or overviews. A comprehensive review of polymers derived from addition polymers of olefins attached to cyclophosphazenes has appeared. Synthesis, copolymerization and quantitative studies of monomer reactivity are discussed in detail. A comprehensive two part review of hybrid phosphazene-siloxane systems includes cyclophosphazenes with siloxane substituents and polymers derived from hydrosilation of alkenylphosophazenes. A survey of new generation candidates for currrently banned Halon fire extinguishing agents concludes that phosphazenes are superior to halons in lab scale extinguishment tests. ... 

The chemistry of phosphorus-nitrogen compounds is well covered in a series of specialized monographs (some concentrating on phosphazenes), the Royal Chemical Society s Specialist Periodical Reports (annual surveys), and numerous review articles (to be cited in the appropriate place of this chapter). 

Introduction.—Few reviews have appeared dealing with more or less general aspects of cyclophosphazene chemistry. The role of cyclophosphazenes as model compounds for reactions of their polymeric analogues has been discussed some fundamental subjects in the area of phosphorus-nitrogen chemistry such as aminolysis, alcoholysis, hydrolysis, and tautomerization phenomena have also been discussed. An extensive review has appeared dealing with reactions of phosphazenes with alkoxides and aryloxides. ... 

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