Polyphosphazenes, chemical structure

When compounds with more comphcated chemical structures were taken into consideration as possible polyphosphazene substituents, the polymers started to show spectroscopic absorptions at wavelengths longer than 240-280 nm. As a consequence, significant photochemical activity started to be observed for POPs, intimately correlated to the photochemical features of these groups. 

Sulfonated aromatic polymers have been widely studied as alternatives to Nafion due to potentially attractive mechanical properties, thermal and chemical stability, and commercial availability of the base aromatic polymers. Aromatic polymers studied in fuel cell apphcations include sulfonated poly(p-phenylene)s, sulfonated polysulfones, sulfonated poly(ether ether ke-tone)s (SPEEKs), sulfonated polyimides (SPIs), sulfonated polyphosphazenes, and sulfonated polybenzimidazoles. Representative chemical structures of sulfonated aromatic polymers are shown in Scheme 3. Aromatic polymers are readily sulfonated using concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or sulfur trioxide. Post-sulfonation reactions suffer from a lack of control over the degree and location of functionalization, and the... 

The poly[organophosphazenes] or polyphosphazenes for short, are a rather new class of polymers of the general chemical structure... 

To conclude this synthetic section, it appears very clear that the experimental approaches for preparation of POPs are very numerous and give accessibility to phosphazene polymers and copolymers with different structures and properties. Moreover, it has been recently estimated [10,383] that the total number of polyphosphazenes reported up to now in the literature is about 700, and that these materials can find potential practical application as flame- and fire-resistant polymers [44,283, 384-388] and additives [389, 390] thermally stable macromolecules [391] chemically inert compounds [392] low temper-... 

Molecular structural changes in polyphosphazenes are achieved mainly by macromolecular substitution reactions rather than by variations in monomer types or monomer ratios (1-4). The method makes use of a reactive macromolecular intermediate, poly(dichlorophosphazene) structure (3), that allows the facile replacement of chloro side groups by reactions of this macromolecule with a wide range of chemical reagents. The overall pathway is summarized in Scheme I. 

Homopolymers possess only one type of repeat unit in the chain structure. Thus, except for the chain ends, the composition is constant throughout the chain. It is also possible to prepare chemical copolymers, in which two chemically different repeat units are distributed along the chain backbone. In terpolymers, there are three different types of repeat units. A chemically copolymeric polyphosphazene is shown in Figure 2.17. Thus, copolymers involve a composition variable since, for example, an AB copolymer... 

This review covers phosphazene literature over the period June 2001 to December 2002 Chemical Abstracts Vols. 135, 136 and 137), and discusses linear phosphazenes including compounds derived thereof (Section 2), cyclophos-phazenes (Section 3) and polyphosphazenes (Section 4). Structural data have been summarized in Section 5. References have been given in Section 6. 

Yashima, E. Maeda, K. Helicity induction on optically inactive polyacetylenes and polyphosphazenes. In Synthetic Macromolecules with Higher Structural Order, Kahn, T. I. M., Ed. ACS Symposium Series 812 American Chemical Society Washington, DC, 2002 pp 41-53. 

Figure 1.10 The synthesis of dendrimeric structures with poly(organo)phosphazene side-arms. DAB diaminobutane and PN polyphosphazene. Reproduced with permission from S.Y. Cho and H.R. Allcock, Macromolecules, 2007, 40, 9, 3115. 2007, American Chemical Society [45]...

From a fundamental physico-chemical point of view, a need exists to compare polyphosphazenes directly with closely related structural analogues in other areas of polymer chemistry. For example, valuable comparisons could be made between polyphosphazenes on the one hand and poly(organosiloxanes) or poly(aldehydes) on the other. Unfortunately, such direct comparisons are not yet possible. The structural analogue of poly(dimethylsiloxane), i.e. [NP(CH3)2]n> not yet been synthesized. Polysiloxanes with alkoxy, aryloxy, or amino residues as the sole side groups are not available. No polyphosphazenes have yet been prepared with two hydrogen atoms on each phosphorus to provide a comparison with poly(oxymethylene). Thus, many synthetic challenges still remain. 

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