Phosphorus nitrogen chain

T)oly (fluoroalkoxyphosphazenes) (PFAP) (I) are semi-inorganic poly-mers that contain a phosphorus nitrogen chain. Pendant fluoroalkoxy groups are attached to the phosphorus to impart hydrolytic stability and hydrocarbon resistance. 

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 largest group of inorganic heteroatomic chain compounds with considerable industrial potential is the phosphazenes,18,23 which are based on a phosphorus-nitrogen skeleton. The electronegativity difference here (xp = 2.19, xn = 3.04) is less than in the siloxane link, but some multiple bonding is involved between N and P, which strengthens the framework. The... 

Polyphosphazenes represent a new approach to the design and synthesis of side-chain liquid crystal polymers. Polyphosphazenes are inorganic main-chain polymers consisting of alternating phosphorus-nitrogen atoms in the main chain with two substituents attached to each phosphorus atom. The top of Figure 1 shows the general structure for a side chain liquid crystal polymer a polymer... 

The content of elements in the nutritional chain is affected by chemical characteristics of the elements, soil composition, plant species, time of harvesting and many other factors. For example, changes of pH of soils after applications of calcium can be manifested in plants by an increased intake of molybdenum and reduced concentrations of copper, iron, manganese and zinc. An increased intake of phosphorus, nitrogen and potassium by plants is manifested by a reduction in the intake of sodium and magnesium by farm animals. Intense fertilization with nitrogen-containing compounds also induces a decrease of the content of copper and zinc in plants, which is manifested adversely in the intake of these elements by animals [5]. 

The conformations of these large rings are irregular and demonstrate the flexibility of the phosphazene chains, which allows the formation of phosphorus-nitrogen rings of practically any size. 

Polyphosphazenes (Figure 4.31) contain alternating phosphorus-nitrogen double and single bonds and side-chain functionalities that can be varied to... 

McWilliams AR, Manners I (2004) Polythionylphosphazenes inorganic polymers with a main chain of phosphorus, nitrogen and sulfiir(VI) atoms. In Gle-ria M, De Jaeger R (eds) (2004) Phosphazenes - a world-wide insight. Nova Science, New York pp 191-208... 

For example, a difunctional reagent (a diamine or diol) could crosslink the chains. Third, as mentioned previously, the possibility exists that the cleavage of phosphorus-nitrogen skeletal bonds might become competitive with phosphorus-halogen bond cleavage. A few examples will illustrate some of the specific restrictions that have been identified. 

The phosphorus-nitrogen bonds of the skeleton are far less susceptible to free-radical induced chain cleavage than are the carbon-carbon or carbon-oxygen bonds of conventional macromolecules. The flame-resistance of most poly-phosphazenes is an added advantage. 

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