Cyclophosphazene monomer

Synthesis of Cyclophosphazene Monomers Containing Vinyl Groups... 

The P-NMR data along with the melting pointT)oiling point data for a few selected cyclophosphazene monomers are given in Table 4.1. 

One of the recent methods that has been applied for preparing polymers containing cyclophosphazene rings as pendant groups is by ring-opening metathesis polymerization (ROMP). The principles involved in the application of this strategy to cyclophosphazene monomers are as follows. 

Cyclolinear polymers contain cyclophosphazenes as a repeat unit of a polymer chain. Cyclomatrix polymers contain crosslinked cyclophosphazene units. These polymers have not been studied as well as the other members of the phosphazene polymer family. Some of the strategies that have been employed for the preparation of these types of polymers are discussed in this section. The preparation of cyclolinear polymers depends on the design of cyclophosphazene monomers that retain two reactive sites. A few strategies for achieving the synthesis of such monomers are shown in Fig. 4.21 [17],... 

The task of preparing appropriate cyclophosphazene monomers for cyclolinear polymers consists of the following. N3P3CI6 consists of six reactive P-Cl units. Clearly this compound as such would not be a suitable monomer for preparing soluble cyclolinear polymers. Recall that condensation polymers involving organic monomers relied on difunctional monomers such as diols, diacids, diamines etc. Replacing four chlorine at-... 

The utility and practical applications of the cyclolinear and the cyclomatrix polymers have not yet been established and perhaps this would depend on improved design of the cyclophosphazene monomers. 

However, not all of the vinyloxyphosphazene monomers will undergo radical polymerization) those with amino substituents are unreac-tive. The i C nmr data indicate that these species electronically resemble vinyl ethers (which do not undergo radical polymerization) whereas the reactive derivatives resemble vinyl acetate. These data demonstrate an excellent example of electronic effect transmission in cyclophosphazene systems. 

In phosphazene chemistry, preparation and reactions of small molecule, linear phosphazenes continue to attract interest. This year numerous papers have explored the utility of the aza-Wittig reaction in the synthesis of complex molecules with particular reference to nitrogen heterocycles. In cyclophosphazene chemistry, the shift of emphasis to materials which are monomers themselves or models for phosphazene polymers is apparent. The synthesis and characterization of poly(phosphazenes) is an active area with extensive interest in phosphazene based polyelectrolytes being noted. Solid state NMR has been shown to be a valuable tool for the study of both structure and phase changes in poly(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. ... 

Unlike the isoelectronic cyclophosphazenes only six-membered rings have been well characterized for oligomers of the —NS(0)E— (E = F, Cl, alkyl, aryl or R2N) monomer unit. The trimeric chloride is best prepared by treating of SOClj with sodium azide in... 

The cocrystaUization of latent organic host molecules - such as ureas, perhydrot-riphenylene, cyclophosphazenes, and steroids - with guest molecules produces inclusion complexes (Figure 32.1). If polymerizable monomers can be incorporated... 

Linear one-dimensional polymers have been obtained by polymerisation of various acrylic monomers inside the cavities of (7.345a). Cyclophosphazenes can be used as scaffolds for the construction of muti-site ligands [22]. 

Most of the polymers that contain cyclophosphazenes as pendant groups are prepared by polymerizing cyclophosphazene containing vinyl monomers. The vinyl group is attached to the cyclophosphazene ring either directly or through a spacer group. Recently, alternative procedures are also... 

Since cyclophosphazene-containing vinyl monomers are really a special case of CH2=CHG type of monomers where G is a cyclophosphazene group, in principle all the polymerization methods for polymerizing conventional vinyl monomers should also be equally effective for this system. In practice, however, only the free-radical methods have so far been found to be successful. Recently, ring-opening metathesis polymerization has also been successfully implemented in this system. The apparent limitations of the other methods of polymerization with respect to the cyclophosphazene-containing vinyl monomers arise from the following factors ... 

In the monomers 4 and 5 the vinyl group is directly attached to the cyclophosphazene unit and these monomers are 1,1-disubstituted ethylenes of the type RRC=CH2- Monomer 6 also belongs to this type although the cyclophosphazene is separated from the vinyl unit by means of the phenyl group which ftmctions as a. spacer. 

In all of the above monomers the vinyl group is attached to the cyclo-phosphazene ring by means of a P-C bond. A simpler way of preparing the cyclophosphazene containing vinyl monomers is to use oxygen nucleophiles. 

The cyclophosphazene group does not undergo degradation during the process of polymerization. The P-NMR chemical shifts of the co-polymers are similar to those observed for the monomers. 

The maximum incorporation of cyclophosphazene in the copolymer occurs in the case of the least sterically hindered monomer 6 (in the copolymer 20). The maximum amount of cyclophosphazene incorporation in 20 has been estimated to be about 67%. In contrast, the incorporation of the sterically hindered monomer N3P3F5[C(CH3)=CH2] 4 in its polystyrene copol nners 19 is considerably less. Up to a maximum of 38% incorporation has been observed. 

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