Polyphosphazenes history

Of course, not all the phosphazene polymers that have been synthesized are equally important. Many of them, in fact, have a mere academic or speculative interest, and will not be described in this article. A few other classes of POPs, however, do occupy an important place in phosphazene history, and have been seriously considered for industrial development and commercialization. These polymers are basically those in which the properties of the inorganic -P=N- skeleton overlap to the highest extent those of the phosphorus side substituents. In the successive sections of this article we will describe in some detail the most important classes of polyphosphazenes that fulfil this condition. 

Aspects of phosphazene research " and of the history of phosphazenes have been examined. The prototrope equilibrium (Scheme 13) between the polyaminophosphines (NH form) and the polyiminophosphines (polyphosphazene or PH form) has been studied by Quantum Mechanical ab initio calculations. When R = H, the energy difference is in favour of the NH tautomer, but if R = NH2 the more stable is the polyphosphazene form. In fact, the preference for the later increases with the electronegativity of the R substituent, and in agreement with the experimental facts, the calculations showed that the polymerization of the monophosphazanes (1) (see Section 1) should be favourable when the electronegativity of R is about 3. The polyhydrido phosphazene has an helical structure with small bond alternation. The calculations also support the mechanisms for the formation of the polyhydridophosphazene (3) from tris(amino)phosphine P(NH2)3 (la) via its phosphazene (NH2)2HP=NH (2a) tautomer. ... 

The vdues of A// for other polyphosphazenes are also reported in Table 4.4. Unfortunately, the data reported are difficult to compare, since the past history of the samples studied is not always precisely known. There are also no data on the heats of the isotropic transition of these polyphosphazenes. Dilato-metric studies showed [41, 53] that both transitions in polybistrifluoroethoxy-phosphazene are accompanied by a marked abrupt change in volume (Fig. 4.17). It was found that the relative changes in the volume on melting and at the isotropic transition are close, 6%. Similar results have been obtained for poly-... 

The morphology of the crystalline phase and the mesophase is correlated. They are both a function of the method of preparation of the samples, their past thermal history, and the defectiveness of the structure of the macromolecule [65]. Crystalline films of polyphosphazenes, polybistrifluoroethoxyphosphazene in particular, prepared from solution have a spherulitic structure which is preserved after melting of the crystalline phase to a total isotropic transition [41,53,57,62, 66]. On the contrary, optically anisotropic mesomorphic regions in the shape of rods in the microscope, which produce the beginning of crystals of the same... 

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