Phosphazene side groups

PHOSPHINE-BOUND TRANSITION METAL CATALYSTS VINYL POLYMERS WITH PHOSPHAZENE SIDE GROUPS... 

Vinyl polymers with phosphazene side groups... 

A number of recently reported synthetic methods include the formation of organic polymers with pendent cyclic or linear phosphazene side groups (reactions 7-9) and a process for the preparation of linear polymers in which phosphazene rings are linked together by organic oligomer chains using acyclic diene metathesis (ADMET) techniques (reaction 10). ... 

The data produced to date suggests that if the poly(organo) phosphazene side groups are carefully selected, the degradation products are nontoxic [25, 48, 69]. That the backbone degradation products consist of a benign mixture of phosphates and ammonia is well proven [46]. Phosphates have a well-known metabolic... 

However, membranes were not prepared from solution casting due to the crystalline form of the sulfonated polymer. In another report by Fei et al., a hybrid polymer with a polynorbomene backbone and pendent sulfonated cyclic phosphazene side groups was synthesized [93]. Co gamma radiation cross-linking was applied after the polymer film was cast, in order to restrict water swelling. The prepared membranes had relatively low lEC ranging from 0.267 to 0.49 mmol g. It was also found that there... 

Fei, S.-T., Wood, R. M., Lee, D. K., Stone, D. A., Chang, H.-L., AUcock, H. R., Inorganic-organic hybrid polymers with pendent sulfonated cychc phosphazene side groups as potential proton conductive materials for direct methanol fuel cells. Journal of Membrane Science, 2008, 320, 206-214. 

Phosphazene polymers are inherently good electrical insulators unless side-group stmctures allow ionic conduction in the presence of salts. This insulating property forms the basis for appHcations as wire and cable jackets and coatings. Polyphosphazenes also exhibit excellent visible and uv radiation transparency when chromophoric substituents are absent. 

Poly[bis(amino)phosphazenes] XVI and a series of polyphosphazenes bearing Methoxy-ethoxyethoxy and alkylamine side groups XVII have been synthesized and complexed with LiCl04 by Chen-Yang [623,624]. 

The connection between hydrophobicity and tissue compatibility has been noted for classical organic polymers (19). A key feature of the polyphosphazene substitutive synthesis method is the ease with which the surface hydrophobicity or hydrophilicity can be fine-tuned by variations in the ratios of two or more different side groups. It can also be varied by chemical reactions carried out on the organo-phosphazene polymer molecules themselves or on the surfaces of the solid materials. 

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

With this synthetic and molecular structural diversity, polyphosphazene chemistry has developed into a field that rivals many areas of organic polymer chemistry with respect to the tailored synthesis of polymers for specific experimental or technological uses. Indeed, hybrid systems are also available in which organic polymers bear phosphazene units as side groups. This is discussed in another Chapter. 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

Figure 6. General structure for phosphazenes with mesogenic side groups. Example is a mixed substituent polymer (VII) where R represents the trifluoroethoxy group and the mesogen with flexible spacer is represented by the curlicue and rectangular box.

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)... 

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... 

Cyclic and High-Polymeric Phosphazenes as Carrier Molecules for Carboranyl, Metallo, or Bioactive Side Groups... 

Metallophosphazenes with Phosphorus-Metal Bonds. Until recently, the chemistry of cyclic and high polymeric phosphazenes was essentially the chemistry of their organic derivatives (Scheme 1). However, a discovery reported in 1979 (31) opened up a new field of metallophosphazene chemistry in which transition metals form the nucleus of the side group structure and are linked to the skeleton through phosphorus-metal bonds. These species are of theoretical and potentially practical importance, and I will summarize briefly some of the main features known at this time. 

A number of liquid crystalline polyphosphazenes with mesogenic side groups have been prepared (48—50). Polymers with nonlinear optical activity have also been reported (51). Polyphosphazene membranes have been examined for gas, liquid, and metal ion separation, and for filtration (52—54). There is interest in phosphazene—organic copolymers, blends, and interpenetrating polymer networks (IPNs) (55—61) to take advantage of some of the special characteristics of phosphazenes such as flame retardance and low temperature flexibility. A large number of organic polymers with cydophosphazene substituents have been made (62). 

In addition to linear polyphosphazenes with one type of side group, as shown in 3.1, other molecular architectures have also been assembled. These include polyphosphazenes in which two or more different side groups, R1 and R2, are arrayed along the chain in random, regular, or block distributions (3.2-3.4). Other species exist with short phosphazene branches linked to phosphorus atoms in the main chain (3.5,3.6). Also available are macromolecules in which carbon or sulfur replace some of the phosphorus atoms in... 

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