Polyphosphazene
Encyclopedia
Polyphosphazenes are a class of inorganic
polymer
s with the repeat unit
(-RR'P=N-). The substituents R,R' are usually alkoxy, amino, (R2N), or halogens (such as chloride
or fluoride
).
Ball-and-stick model
of part of a poly(difluorophosphazene) chain, (NPF2)n.
Polyphosphazenes are typically prepared by the thermal ring-opening polymerization of hexachlorophosphazene
(Cl2PN)3 followed by esterification of the intermediate poly(dichlorophosphazene)
with either amines or sodium
salts of alcohols
:
These polymers were popularized by the research group of Harry R. Allcock
at Pennsylvania State University
.
Polyphosphazenes containing polyether side chains are good ionic conductors for lithium triflate. They are among the few polymers that will dissolve such salts. Similarly, the incorporation of acidic functional units into the side groups of polyphosphazene yields proton conductor
s.
Inorganic chemistry
Inorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
s with the repeat unit
Repeat unit
An essential concept which defines polymer structure, the repeat unit or repeating unit is a part of a polymer chain whose repetition would produce the complete polymer by linking the repeat units together successively along the chain, like the beads of a necklace.A repeat unit is sometimes called...
(-RR'P=N-). The substituents R,R' are usually alkoxy, amino, (R2N), or halogens (such as chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
or fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
).
Ball-and-stick model
Ball-and-stick model
In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them...
of part of a poly(difluorophosphazene) chain, (NPF2)n.
Polyphosphazenes are typically prepared by the thermal ring-opening polymerization of hexachlorophosphazene
Hexachlorophosphazene
Hexachlorophosphazene is an inorganic compound with the formula 3. The molecule has a cyclic backbone consisting of alternating phosphorus and nitrogen atoms. It can be viewed as a trimer of the hypothetical compound N≡PCl2...
(Cl2PN)3 followed by esterification of the intermediate poly(dichlorophosphazene)
Poly(dichlorophosphazene)
poly, also called dichlorophosphazine polymer or phosphonitrilechloride polymer, is chemical compound with formula n...
with either amines or sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
salts of alcohols
Alkoxide
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands...
:
- n (Cl2PN)3 → (Cl2PN)3n3n + Nu- → (Nu2PN)3n + 6n Cl-
- where Nu- = NR2-, OR-, F-
These polymers were popularized by the research group of Harry R. Allcock
Harry R. Allcock
Harry R. Allcock is Evan Pugh Professor of chemistry at Pennsylvania State University.Harry Allcock obtained his B.S. in 1953 and his Ph.D. in 1956, both at the University of London. He is notable for his work on the "inorganic rubbers" with a phosphorus-nitrogen backbone . With James E...
at Pennsylvania State University
Pennsylvania State University
The Pennsylvania State University, commonly referred to as Penn State or PSU, is a public research university with campuses and facilities throughout the state of Pennsylvania, United States. Founded in 1855, the university has a threefold mission of teaching, research, and public service...
.
Properties
The properties of polyphosphazenes depend on the nature of the side groups. Most polyphosphazenes are colorless and exhibit high thermal stability, although they are somewhat sensitive to base hydrolysis. For certain alkoxides (e.g. OCH2CF3, derived from trifluoroethanol), the polymers are highly flexible with very low glass transition temperatures. In this respect the polymers resemble the commercially significant siloxanes.Polyphosphazenes containing polyether side chains are good ionic conductors for lithium triflate. They are among the few polymers that will dissolve such salts. Similarly, the incorporation of acidic functional units into the side groups of polyphosphazene yields proton conductor
Proton conductor
A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ are the primary charge carriers.-Composition:For practical applications, proton conductors are usually solid materials. Typical materials are polymers or ceramic. Typically the pores in practical materials are small...
s.