Phosphorus-nitrogen polymers

Synthesis of Phosphorus-Nitrogen Polymers by Using Silicon-Nitrogen-Phosphorus Reagents... 

The most numerous and best known phosphorus-nitrogen polymers are... 

Phosphorus-Nitrogen Polymers. The most extensively investigated class of such polymers is the polyphosphazenes, which have been reviewed in regard to flame retardancy (143) and which are discussed in a separate article in this Encyclopedia. Research on polymeric phosphonamides, phosphoramides, and phosphorimides has not as yet led to commercial results. 

We might expect, therefore, to find phosphorus/nitrogen polymers, (R2PN) , analogous to the silicones, (R2SiO) , that we looked at in Section 10.3. These polymers are indeed known and are called polyphosphazenes in recent years they have found various practical applications. 

An overview of the synthesis and characterization of a unique class of polymers with a phosphorus-nitrogen backbone Is presented, with a focus on poly(dichloro-phosphazene) as a common Intermediate for a wide variety of poly(organophosphazenes). Melt and solution polymerization techniques are Illustrated, Including the role of catalysts. The elucidation of chain structure and molecular weight by various dilute solution techniques Is considered. Factors which determine the properties of polymers derived from poly(dichlorophos-phazene) are discussed, with an emphasis on the role that the organic substituent can play In determining the final properties. 

The study of open-chain polyphosphazenes has attracted Increasing attention In recent years, both from the standpoint of fundamental research and technological development. The polyphosphazenes are long chains of alternating phosphorus-nitrogen atoms with two substituents attached to phosphorus. These polymers have been the subject of several recent reviews (1-3). Interest has stemmed from the continuing search for polymers with improved properties for existing applications as well as for new polymers with novel properties. 

The stable form of nitrogen at room temperature is N2, which has an extraordinarily strong (946 kJ mol-1) triple bond In contrast, white phosphorus consists of P4 molecules (see Chapter 16), and the thermodynamically stable form is black phosphorus, a polymer. At temperatures above 800 °C dissociation to P> molecules does take place, but these are considerably less stable than N2 with a bond energy of488 kJ mol 1. In this case. too. in the heavier element several single bonds arc more effective than the multiple bond. 

Ceramic-type materials that contain no organic linkage units can be prepared by the pyrolysis of cyclic or high polymeric aminophosphazenes. An example is shown in reaction (44). Under appropriate conditions, pyrolysis products that correspond to phosphorus-nitride are formed. Polyphosphazenes that contain both amino and borazine side groups yield phosphorus-nitrogen-boron ceramics following pyrolysis 94,95 The conversion of a formable polymer into a ceramic has many potential advantages for the controlled synthesis and fabrication of advanced ceramics. This principle is discussed in more detail in Chapter 9. 

In this paper, the surface grafting of rayon fabrics with nitrogen and phosphorus containing polymers in cold plasma is studied. The analytical data (IR spectroscopy, TGA, electron microscopy, elemental analysis, etc.) indicate the formation of grafted copolymers. The grafted rayon fabrics present improved flame-retardant properties, the best behavior was proved by those grafted with polyurea of phosphinic acid. 

Our investigations suggest that grafted copolymers are obtained probably by the recombination reactions of the macroradicals generated both on the cellulosic support and on the nitrogen and phosphorus containing polymers. 

It can be presumed that under cold plasma conditions, the nitrogen and phosphorus containing polymers can lead also to the macroradicals through dehydrogenation of CH aromatic and aliphatic or NH groups. 

FIGURE 6.6 Phosphorus-nitrogen intumescent flame retardant. (From Gao, F. et al., Polym. Deg. Stab., 91, 1295, 2006.)... 

Moreover, the development of new strategies for surface modifications of nanoparticles with compounds having FR activity could provide a new field of research on FR systems. The use of novel phosphorus-, nitrogen-, or halogen-containing modifiers, instead of alkylammonium ions, for layered silicates seems promising. FR action conferred by the surface modifier can be combined with action due to composite morphology, particularly when the host polymer is a polymer blend instead of a pure polymer. 

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