Phosphazenes, generalizations

Methylcarbazolyl/methylcarbazolyl, methylanthryl Copoly(phosphazenes) (General formula [(RO) i(R O) 2- PN] ) R R Phenyl/p-ethylphenylene 100-94 frans-Planar XRl 27... 

In this context, phosphoranimine compoimds (both homosubstituted with an unique group or bearing two different groups at the phosphorus) play a fundamental role because their polymerization under different experimental conditions eventually leads to fully substituted polyphosphazenes with no residual chlorines on the phosphazene skeleton. The general scheme of the phosphoranimine polymerization processes is reported in Fig. 10. 

The general conclusion is that the phosphazene macromolecules synthesized and characterized up to now show a large range of properties and that they can potentially be exploited in many different applicative domains. 

Table 9 General characteristics of fluorinated phosphazene polymers and copolymers ...

The most known and investigated substrate of this class is poly[bis(trifluo-roethoxy)phosphazene], PTFEP, a polymer formally derived by the general formula above by putting x=y=l and Z=R The general structure of this compound is shown below. 

When x=l and y=2,3,4,. and Z=H or F, a new class of polyphosphazene substrates is obtained, which derive from the simultaneous substitution of two different fluorinated alcohols of different lengths on the same polydichloro-phosphazene macromolecule. The general structure of the substrates is reported below. 

In the frame of photochemical research, phosphazene polymers have also been exploited in combination with external reagents able to selectively absorb impinging light and induce reactivity on these materials. The general reaction scheme is shown below. 

Although poly(organo)phosphazenes have been characterized using dilute solution techniques (4-10), attempts to characterize polydichlorophosphazene directly have been limited (11,12,13). The presence of gel and the fact that polydichlorophosphazene is moisture sensitive generally have precluded an accurate analysis of its molecular weight and molecular weight distribution... 

This chapter covers the literatures of phosph(v)azenes. The general pattern of development in this area is similar to that observed in previous yearly reviews with additional interest being shown in polyphosphazenes and in a variety of molecular orbital calculations of both linear and cyclic phosphazenes. 

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.

The true value of the chloropolymer (I) lies in its use as an intermediate for the synthesis of a wide variety of polytorgano-phosphazenes) as shown in Figure 1. The nature and size of the substituent attached to the phosphorus plays a dominant roll in determining the properties of the polyphosphazene. Homopolymers prepared from I, in which the R groups are the same or, if different, similar in molecular size, tend to be semi-crystalline thermoplastics. If two or more different substituents are introduced, the resulting polymers are generally amorphous elastomers. (See Figure 1.)... 

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. 

In summary, this new and general method of synthesizing both cyclic and polymeric phosphazenes (eq 6)... 

Temperature intervals between the Tg and the Tm of polyphosphazenes are unusually small and generally fall outside the frequently cited empirical relation 0.5 < Tg/Tm (K) 0.67. This behavior could be related to complications in the first-order transition generally found with organo-substituted phosphazenes. Two first-order transitions within a temperature interval of... 

IF the product were a monomer, its structure could be drawn as Cl2PsN, which is analogous to organic nitriles. R—C=N. For this reason the original names used for these compounds were phosphonitriles, phosphonitrilic chloride, etc. However, the products are actually either cyclic or linear polymers of general formula [NPC ,] . Thus, by analogy with benzene, borazine. etc., these compounds hove become known as phosphazenes. The rn jor product of the reaction in Eq. 16.47 and the easiest to... 

The amides of phosphorus can be similarly obtained, using either PC13, POCl3 or PC1S, for example.24 27 However, with PC15 only secondary amines yield amides,27 primary amines generally giving phosphazene derivatives.28... 

All phosphazenes, whether cyclic or chain-like, contain the formally unsaturated group P=N with four-coordinate P and two-coordinate N atoms. Based on available experimental data, the following generalizations may be made in regard to their structure and properties ... 

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