Inorganic polymers: examples and applications

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

In nature, there are organoelement, organic and inorganic polymers. Inorganic materials include materials whose main chain is inorganic, and the side branches are not hydrocarbon radicals. Elements of III-VI groups of the periodic table of chemical elements are most prone to the formation of polymers of inorganic origin.

Classification

Organic and inorganic polymers are being actively studied, their new characteristics are being determined, so a clear classification of these materials has not yet been developed. However, certain groups of polymers can be distinguished.

Depending on structure:

• linear;
• flat;
• branched;
• polymer nets;
• three-dimensional and others.

Depending on the backbone atoms that make up the polymer:

• homochain type (-M-)n – consist of one kind of atoms;
• heterochain type(-M-L-)n - consist of different types of atoms.

Depending on origin:

• natural;
• artificial.

To classify substances that are macromolecules in the solid state as inorganic polymers, they must also have a certain anisotropy of the spatial structure and corresponding properties.

Key Features

More common are heterochain polymers, in which alternation of electropositive and electronegative atoms occurs, for example, B and N, P and N, Si and O. Get heterochain inorganic polymers (NP) can be using polycondensation reactions. The polycondensation of oxoanions is accelerated in an acidic medium, while the polycondensation of hydrated cations is accelerated in an alkaline medium. Polycondensation can be carried out both in solution and in solids in the presence of high temperature.

Many heterochain inorganic polymers can only be obtained under conditions of high-temperature synthesis, for example, directly from simple substances. The formation of carbides, which are polymeric bodies, occurs when certain oxides interact with carbon, as well as in the presence of high temperature.

Long homochain chains (with degree of polymerization n>100) form carbon and group VI p-elements: sulfur, selenium, tellurium.

Inorganic polymers: examples and applications

The specificity of NP lies in educationpolymeric crystalline bodies with a regular three-dimensional structure of macromolecules. The presence of a rigid framework of chemical bonds provides such compounds with significant hardness.

This property makes it possible to use inorganic polymers as abrasive materials. The use of these materials has found the widest application in the industry.

The exceptional chemical and thermal resistance of NP is also a valuable property. For example, reinforcing fibers made from organic polymers are stable in air up to a temperature of 150-220 ˚C. Meanwhile, boron fiber and its derivatives remain stable up to a temperature of 650 ˚С. That is why inorganic polymers are promising for creating new chemically and heat-resistant materials.

Practical value is also of NP, which are both close in properties to organic, and retain their specific properties. These include phosphates, polyphosphazenes, silicates, polymeric sulfur oxides with various side groups.

Carbon polymers

Assignment: “Give examples of inorganic polymers,” often found in chemistry textbooks. It is advisable to carry it out with the mention of the most outstanding NP - carbon derivatives. After all, this includes materials with unique characteristics: diamonds, graphite and carbine.

Carbine is an artificially created, little-studied linear polymer with unsurpassed strength indicators that are not inferior, but according to a number of studies andsuperior to graphene. However, carbine is a mysterious substance. After all, not all scientists recognize its existence as an independent material.

Outwardly looks like a metal-crystalline black powder. It has semiconductor properties. The electrical conductivity of carbyne increases significantly under the action of light. It does not lose these properties even at temperatures up to 5000 ˚С, which is much higher than for other materials of this purpose. The material was received in the 60s by V. V. Korshak, A. M. Sladkov, V. I. Kasatochkin and Yu. P. Kudryavtsev by catalytic oxidation of acetylene. The most difficult thing was to determine the type of bonds between carbon atoms. Subsequently, a substance with only double bonds between carbon atoms was obtained at the Institute of Organoelement Compounds of the USSR Academy of Sciences. The new compound was named polycumulene.

Graphite - in this material polymer ordering extends only in the plane. Its layers are connected not by chemical bonds, but by weak intermolecular interactions, so it conducts heat and current and does not transmit light. Graphite and its derivatives are fairly common inorganic polymers. Examples of their use: from pencils to the nuclear industry. By oxidizing graphite, intermediate oxidation products can be obtained.

Diamond - its properties are fundamentally different. Diamond is a spatial (three-dimensional) polymer. All carbon atoms are held together by strong covalent bonds. Because this polymer is extremely durable. Diamond does not conduct current and heat, has a transparent structure.

Boron polymers

If you are asked what inorganic polymers you know, feel free to answer - boron polymers (-BR-). This is a fairly extensive class of NPs, widely used in industry and science.

Boron carbide - its formula looks more correct like this (B12C3) n. Its unit cell is rhombohedral. The framework is formed by twelve covalently bonded boron atoms. And in the middle of it is a linear group of three covalently bonded carbon atoms. The result is a very strong structure.

Borides - their crystals are formed similarly to the above-described carbide. The most stable of these is HfB2, which melts only at 3250°C. TaB2 is noted for the highest chemical resistance - neither acids nor their mixtures act on it.

Boron nitride - often referred to as white talc for its resemblance. This similarity is really only superficial. Structurally, it is similar to graphite. Get it by heating boron or its oxide in an ammonia atmosphere.

Borazon

Elbor, borazone, cyborite, kingsongite, cubonite are superhard inorganic polymers. Examples of their application: the manufacture of grinding wheels, abrasive materials, metal processing. These are chemically inert substances based on boron. Hardness is closer than other materials to diamonds. In particular, borazon leaves scratches on diamond, the latter also leaves scratches on borazon crystals.

However, these NDs have several advantages over natural diamonds: they have a greaterheat resistance (withstand temperatures up to 2000 ° C, diamond is destroyed at rates in the range of 700-800 ° C) and high resistance to mechanical stress (they are not so fragile). Borazon was obtained at a temperature of 1350 °C and a pressure of 62,000 atmospheres by Robert Wentorf in 1957. Similar materials were obtained by Leningrad scientists in 1963.

Inorganic sulfur polymers

Homopolymer - this modification of sulfur has a linear molecule. The substance is not stable, with temperature fluctuations it breaks up into octahedral cycles. It is formed in the case of a sharp cooling of the sulfur melt.

Polymer modification of sulfur dioxide. Very similar to asbestos, has a fibrous structure.

Selenium polymers

Grey selenium is a polymer with helical linear macromolecules nested in parallel. In chains, selenium atoms are covalently bonded, while macromolecules are linked by molecular bonds. Even molten or dissolved selenium does not break down into individual atoms.

Red or amorphous selenium is also a polymer of a chain, but of a slightly ordered structure. In the temperature range of 70-90 ˚С, it acquires rubber-like properties, turning into a highly elastic state, which resembles organic polymers.

Selenium carbide, or rock crystal. Thermally and chemically stable, sufficiently strong spatial crystal. Piezoelectric and semiconductor. Under artificial conditions, it was obtained by reacting quartz sand and coal in an electric furnace at a temperature of about 2000 ° C.

Other Selenium Polymers:

• Monoclinicselenium - more ordered than amorphous red, but inferior to gray.
• Selenium dioxide, or (SiO2)n, is a three-dimensional network polymer.
• Asbestos is a polymer of selenium oxide with a fibrous structure.

Phosphorus polymers

There are many modifications of phosphorus: white, red, black, brown, purple. Red - NP fine-crystalline structure. It is obtained by heating white phosphorus without air at a temperature of 2500 ˚С. Black phosphorus was obtained by P. Bridgman under the following conditions: pressure 200,000 atmospheres at a temperature of 200 °C.

Phosphornitride chlorides are compounds of phosphorus with nitrogen and chlorine. The properties of these substances change with increasing mass. Namely, their solubility in organic substances decreases. When the molecular weight of the polymer reaches several thousand units, a rubbery substance is formed. It is the only sufficiently heat-resistant carbon-free rubber. It only breaks down at temperatures above 350 °C.

Conclusion

Inorganic polymers are mostly substances with unique characteristics. They are used in production, in construction, for the development of innovative and even revolutionary materials. As the properties of known NPs are studied and new ones are created, the scope of their application expands.