Inorganic rubber

These last named materials may be considered as derivatives of the inorganic rubber, polyphosphonitrilic chloride, discovered by Stokes in 1895. This was prepared by the reaction of phosphorus pentachloride with ammonium chloride as follows ... 

In the mid-1970s Firestone announced the availability of PNF Rubber. This rubber has been discussed in Section 13.10 and whilst referred to as a poly(fluoroalkoxyphosphazene) may be considered to be a direct descendant of the inorganic rubber first prepared by Stokes in 1895. 

As early as 1895, the synthesis of polydichlorophosphazene was attempted by H.N. Stokes by thermal ring-opening polymerization of hexachloro-triphosphazene [(NPCl2)3]. The product obtained by H.N. Stokes was a high-molecular weight cross-linked rubbery material called inorganic rubber which is insoluble in all solvents and hydrolytically decomposes into phosphates, ammonia, and hydrochloric acid in the presence of moisture. Because of its insolubility and hydrolytic instability, the polymer found no technological application and remained as a laboratory curiosity. 

Since the initial disclosure by Allcock, workers have sought to answer various questions 1) What is the nature of the polymerization process (mechanism) 2) What is the structure of poly(dichlorophosphazene) that distinguishes it from the insoluble "inorganic rubber (III) 3) The substitution process gives a seemingly endless variety of products. What are the limitations or... 

Figure 2.42 Stress-temperature data on inorganic rubber, in which the upturns in the stress at low temperatures illustrate the reinforcing effects of strain-induced crystallization.73 Reproduced by permission of Pergamon Press.

Stokes was the first person to prepare a polymeric form of these species. He reported that any of the small-molecule cyclic chlorophosphazene compounds, when heated, were transformed into a rubbery material that was later called inorganic rubber. 11 This material swelled in organic solvents such as benzene but it did not dissolve. Stokes also described how inorganic rubber decomposed to reform the cyclic compounds when heated to high temperatures under reduced pressure. His accomplishments at that time are all the more remarkable because these compounds are sensitive to a moist atmosphere in which they are hydrolyzed to ammonium phosphate and hydrochloric acid. 

Use Refractories, especially for steel furnace linings, poly crystalline ceramic for aircraft windshields, electrical insulation, pharmaceuticals and cosmetics, inorganic rubber accelerator, oxychloride and oxysulfate cements, paper manufacture, fertilizers, removal of sulfur dioxide from stack gases, adsorption and catalysis, semiconductors, pharmaceuticals, food and feed additive. 

The chemical origins of this field can be traced back over 150 years to the reports by Liebig, Wohler, and Rose [12,13] that phosphorus pentachloride and ammonia react to yield a white, crystalline, "organic"-type compound since shown to be hexachlorocyclotriphosphazene (5). Later, in 1897, Stokes [14] described the conversion of this compound to an insoluble, hydrolytically sensitive elastomer subsequently known as "inorganic rubber". The intractibility of inorganic rubber is now known to be due to its crosslinked structure, and its hydrolytic sensitivity to the presence of phosphorus-chlorine bonds. 

Butyraldehyde-aniline condensation product Lead dimethyidithiocarbamate accelerator, inorganic rubber Magnesium oxide accelerator, IR... 

The poorly reproducible polymerization is presumably initiated by traces of cationic impurities. The poly(phosphonitrile chlorides) or poly(dichloro-phosphazenes), II, mostly have PCI3 end groups. They depolymerize at higher temperatures to hexachlorocyclotriphosphazene, I, and octachlorocyclo-tetraphosphazene and hydrolyze even in moist air. The products obtained at high yield are cross-linked and exhibit all the properties of inorganic elastomers. Consequently, they are also called inorganic rubbers. 

For other polar substances a region of ideal elasticity is observed, and has been experimentally verified for polyvinyl acetate and for the inorganic rubbers. 

The Stokes s inorganic rubber [NPCUJn did not dissolve in common organic solvents because it was an extensively crosslinked polymer. This suggestion is also home out by the swelling of this polymer in solvents. It is known that crosslinked organic polymers also swell in solvents. 

The degradation of the Stokes s inorganic rubber [NPCUJn in atmosphere occurs presumably because of the sensitivity of the P-Cl bonds towards the hydrolysis reaction. 

Any efifort to make the inorganic rubber into a viable material, therefore, needed to concentrate on solving the above two problems. 

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