Poly phosphazenes

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).  

0)xM]CH20(CH2CH20)yMe (x=l-3, y=l-3)], are available from the sodium salts of the parent alcohols (ROH). Aqueous solutions of the polymers are soluble below the lower critical solubility temperature (LCST) and precipitate above the LCST. Cross-linked films were also examined as hydrogels. The enthalpies of phase separation from water were determined by DSC and found to be related to the determined LCST. Mixed substituent 2-(2-methoxyethoxy)ethoxy and 

Miscellaneous applications of poly(phosphazenes) include ter-butoxycarbonyl protected materials for chemically amplified resists in microlithographythin film electroluminescent devices,optical wave guides, aryloxy derivatives as components of fire-, heat- and impact-resistant materials and components of a low-density, thermoplastic elastomeric, ablative insulation for rocket motors.  

The following compounds have been examined by diffraction methods. All distances are in picometers and angles in degrees. 

Mo(PNMc2)NRAr)3 R=C(CD3)2CH3 Ar=3,5-C6H3Me2 Preliminary data linear MoPN 81 

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As expected, the TgS of the hybrid sulfanuric-phosphazene polymers are much closer to the values reported for poly(phosphazenes) than those of sulfanuric polymers (vide supra). The values for the polymers 14.10a... 

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). 

The poly(phosphazene) backbone can be made to be part of a fully inorganic polymer by replacing the organic substituents with chlorines, thus generating poly(dichlorophosphazene). However, this is a reactive molecule and is more usually employed as the starting material for the preparation of the various partially organic poly(phosphazenes). 

Among other uses, these polymers have been employed in a variety of biomedical applications. Poly(phosphazenes) containing organic side chains, derived from the anaesthetics procaine and benzocaine, have been used to prolong the anaesthetic effect of their precursor drugs. They have also been used as the bioerodable matrix for the controlled delivery of drugs. 

Payne LG, Jenkino SA, Adrianov A, Langer R, and Robert BE. Xenobiotic pol3nners as vaccine vehicles. In Mestecky J (ed). Advances in Mucosal Immunology. New York Plenum Press, pp. 1475-1480. Ibim SM, Ambrosio AA, Larrier D, Allcock HR, and Laurencin CT. Controlled macromolecule release from poly(phosphazene) matrices. J Control Release, 1996, 40, 31-39. 

Regardless of the way in which polydichlorophosphazene is prepared (vide supra), this polymer should be handled almost immediately because of the extreme reactivity of the chlorine atoms attached to the phosphorus of the poly-phosphazene chain toward nucleophilic groups and water. 

As reported in Table 5 and in other recent publications [399,491 ], polymers with very low Tg are expected when the inherent skeletal flexibihty of poly-phosphazenes is coupled with fluorinated alcohols of low dimensions and/or of high chain mobility. In fact, the Tg values for POPs substituted with fluorinated alcohols vary between -50 °C and -90 °C, confirming the extreme chain mobility of these polymers and the existence in them of very low torsional energy barriers. 

Based on the synthesis of polyphosphazenes and of diblock copolyphosp-hazenes by the living cationic polymerization of phosphoranimines [237,241], the triblock poly(phosphazene-ethylene oxide) copolymer XVIII was synthesized by Allcock [223]. 

A recent development has been the synthesis of bioerodible poly-phosphazenes that bear glyceryl side groups (35). The synthesis of these polymers requires a protection-deprotection sequence to reduce the functionality of the glycerol and prevent crosslinking. 

Allcock, H. R., and Kwon, S., An ionically-crosslinkable poly-phosphazene Poly[di(carboxylatophenoxy)phosphazene] and its hydrogels and membranes. Macromolecules. 22. 75, 1989. 

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-... 

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. 

In recent years, many poly(phosphazenes), [RoPN]n, with a variety of substituents at phosphorus have been prepared and they often exhibit useful properties including low temperature flexibility, resistance to chemical attack, flame retardancy, stability to UV radiation, and reasonably high thermal stability. (1,2) Compounds containing biologically, catalytically, or electrically active side groups are also being investigated. (3,4)... 

All of the soluble polymers (1 and 3-6) give high resolution NMR spectra (1H, 13C, and 31P) that are completely consistent with their proposed structures. As observed for other types of poly(phosphazenes), the 31P chemical shifts of these alkyl/aryl substituted polymers are consistently ca. 15-30 ppm upfield from those of the analogous cyclic trimers and tetramers. Some important structural information is provided by 13C NMR spectroscopy, particularly for the phenyl/alkyl derivatives 3 and 4. These polymers are rare examples of phos-phazenes that contain two different substituents at each phosphorus atom in the chain. Thus, they have the possibility of being stereoregular. The fact that the structures are completely atactic, however, is confirmed by the observation of three doublets in the P-Me region of the 13C NMR spectrum (ca. 22 ppm) in a 1 2 1 intensity ratio. 

Thermogravimetric analysis (TGA) of these poly(phosphazenes) shows their decomposition onset temperatures in an inert atmosphere to be ca. 350 to 400°C, depending on the side group. These temperatures are ca. 25-75°C higher than that reported for commercial materials based on the fluoroalkoxy substituted polymer, [(CFgCHjO PN],. (19) Interestingly, methyl rather than phenyl side groups yield the more stable materials, as shown by... 

Tg of-16 °C for the butylamino-substituted hybrid polymer 146 is significantly lower than the value of +8 °C reported for the corresponding poly(phosphazene) [NP(NHtBu)2] as a result of the presence of the small S=0 group. 

Allcock s research led to the development of poly-phosphazene-based PEMs by his small molecule studies of the sulfonation of cyclic trimeric phosphazenes and the surface chemistry of polyphosphazene macromolecules. In a 1993 report, he described the sulfonation of aminophosphazenes with 1,3—propanesultone. While these specific materials are not necessarily ideal as PEMs, this study demonstrated a novel technique for creating sulfonated polyphosphazene materials that may provide more control over the sulfonated polymer product than wholesale sulfonation of a base polymer by a strong sulfonating agent. 

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. 

The phosphoranimine route also allows an alternate route to poly(dichlorophosphazene) by using lV-(trimethylsilyl)-/)/)/>-trichlorophosphoranimine as the monomer. The phosphoranimine route not only efficiently produces alkyl and aryl poly(phosphazene)s but also offers... 

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