Phosphazene High Polymers

Allcock, H. R., and Fuller, T. J., Phosphazene high polymers with steroidal side groups. Macromolecules. 13, 1338, 1980. 

Work on phosphazene high polymers continues to attract increased interest. Advances in the study of the ring-opening polymerization, and physical characterization in the solid state, of the materials produced by these reactions have been reported. 

Macromolecular Substitution Route. The current surge in poly-phosphazene research Is mainly a result of the development in the mid 1960 s (2-4) of a substitutive route to the synthesis of organo phosphazene high polymers. Before that time, only a sporadic interest in the subject existed because the known polymers, cross linked poly(dihalophosphazenes), (1,5) were insoluble and hydrolytically unstable. 

For these reasons, small molecules have played a crucial role in the development of phosphazene high-polymer chemistry.117 In particular, the substitution reactions, reaction mechanisms, NMR spectroscopy, and X-ray diffraction analysis of small-molecule cyclic phosphazenes, such as 3.2 or 3.3 have provided information that could not be obtained directly from the high polymers. 

In this paper we consider two specific challenges. First, how might transition metals be linked to phosphazene high polymers Such systems are of interest as immobilized catalysts or materials with unusual electrical properties. Second, how can bioactive agents be attached to polyphosphazenes to prepare, for example, targeted, slow release chemotherapeutic agents ... 

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. 

Recent developments in phosphazene high polymer chemistry have been summarized (7). 

Finally, carborane units have been attached to phosphazene high polymers by reactions of lithiocarboranes with (NPCl2) . These reactions are summarized in Eq. 

H.R. Allcock, P.E. Austin, T.X. Neenan, Phosphazene high polymers with bioactive substituent groups prospective anesthetic aminophos-phazenes. Macromolecules 15 (3) (1982) 689-693. 

Allcock, H.R., Pucher, S.R., Fitzpatrick, R.J. and Rashid, K. (1992) Antibacterial acthity and mutagenicity studies of water-soluble phosphazene high polymers. Biomaterials, 13(12), 857-862. 

Allcock H R, Phosphazene high polymers . In Comprehensive Polymer Science, ed. G Allen, 4, Pergamon Press, New York, USA, 1989. 

See Elastopiers.synthetic-phosphazenes Inorganic high polymers. 

Current progress in the synthesis and properties of pyrrolylphosphazenes is summarized. The differences in reactivity of the cyclic trimer (NPC12)3, and high polymer (NPC12)X, toward the pyrrolide nucleophile are discussed. Efforts to induce electronic conductivity in the polyphosphazenes are reviewed with particular emphasis on polybis (pyrrolyl) phosphazene. 

Linkage of Transition Metals to Phosphazene Rings and High Polymers... 

The halogen atoms remaining can then be replaced by organic residues such as trifluoroethoxy units. High polymers can also be prepared by ring-opening polymerization of the chlorocyclo-phosphazene, XXVIII. Compounds of this type can be converted to nldo-carboranes in the presence of base, but these do not form metallo-derivatlves, presumably for sterlc reasons (29). 

Figure 3.5 Schematic representation of the effect of steric hindrance generated by bulky side groups on a cyclic trimeric and a high polymeric phosphazene. Depolymerization of a high polymer to a cyclic trimer relieves the intramolecular crowding.

Most chemists begin their training by learning about small molecules rather than polymers. The reasons for this are both traditional and practical. Small molecules are often easier to synthesize, purify, and characterize than are polymers. Moreover, in phosphazene chemistry it is easier to study small-molecule reactions, reaction mechanisms, and molecular structures than it is to obtain comparable information at the high-polymer level. 

It is exceedingly difficult to determine the molecular structure of a synthetic macromolecule. X-ray diffraction—the ultimate structural tool for small-molecule studies—yields only limited information for most synthetic high polymers, and crucial data about bond lengths and bond angles are difficult to obtain.47 However, that same information can be obtained relatively easily from single crystal X-ray diffraction studies of cyclic trimers, tetramers, and short-chain linear phosphazene oligomers. The information obtained may then be used to help solve the structures of the high polymeric counterparts. 

Figure 3.7 P NMR spectra of cyclic trimeric and high polymeric phenyl-fluoro phosphazenes. Note (1) the shift in the whole spectrum that occurs in moving from a cyclic small-molecule phosphazene to a related high polymer, and (2) the chemical shift and splitting pattern that results from phosphorus coupling to the two fluorine atoms or to one fluorine. Spectra provided by W. D. Coggio.

Phosphazene Rings and High Polymers Linked to Transition Metals or Biologically Active Organic Species... 

Species IV were prepared from -bromophenoxy-substituted phosphazene trimers and high polymers, by metal-halogen exchange to yield the -lithio-derivative, followed by reaction with diphenylchlorophosphine. Both cyclic trimers and high polymers containing the pendent phosphine reacted with H2Os(CO)3q,... 

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). 

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