Alkoxy-substituted polyphosphazenes

For halogen or alkoxy-substituted polymers Tg values are low (between -60 and —100° C). Alkoxy poly phosphazene with Ci - C3 substituents are elastomers. Higher alkoxy- or aryloxy-substituted polyphosphazenes are thermoplastics. Fluoroalkoxypolyphosphazenes exhibit a good stability toward diluted acids and bases. Some of them have outstanding thermal stability and good flame-retardant properties. 

A number of chlorinated and fluorinated alkoxy- and aryloxy-substituted polyphosphazenes has been prepared in order to investigate the influence of the side-group on refractive index and birefringence. " New polymers with (4-ethyleneoxy)phenoxy side groups (267) as well as polymers with a combination of phenoxy and ethyleneoxy groups (268) have been prepared aiming at... 

Properties. One of the characteristic properties of the polyphosphazene backbone is high chain dexibility which allows mobility of the chains even at quite low temperatures. Glass-transition temperatures down to —105° C are known with some alkoxy substituents. Symmetrically substituted alkoxy and aryloxy polymers often exhibit melting transitions if the substituents allow packing of the chains, but mixed-substituent polymers are amorphous. Thus the mixed substitution pattern is deUberately used for the synthesis of various phosphazene elastomers. On the other hand, as with many other flexible-chain polymers, glass-transition temperatures above 100°C can be obtained with bulky substituents on the phosphazene backbone. 

Amino, alkoxy, and aryloxy polyphosphazenes are typically prepared by nucleophilic displacement reactions of poly(dihalophosphazenes). Analogous reactions with organometallic reagents, however, result in chain degradation and cross linking rather than in linear, alkyl, or aryl substituted poly(phosphazenes). The thermolysis of appropriate silicon-nitrogen-phosphorus compounds can be used to prepare fully P—C bonded poly(organophosphazenes). The synthesis of two of these materials and their Si—N—P precursors is described here. 

A partial solution to the problem of difunctional reactivity of alkoxy sulfonate nucleophiles during the macromolecular substitution of PDCP was proposed by Ganapathiappan et al. [25] and is presented in Fig. 5. Here the disodium salt of 2-hydroxyethanesulfonic acid is reacted with an excess of linear PDCP in the presence of a phase-transfer catalyst. A partially substituted, crosshnked semi-product is obtained, which is then treated with another nucleophile, the monofunctional sodium salt of 2-(2-methoxyethoxy)ethanol, to displace the sulfonate groups and chlorines attached to phosphorous atoms. It was found that the amount of sulfonate groups incorporated into the polyphosphazene was generally 50% of that initially used in the reaction mixture. 

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