It is amazing how diverse the objects around us and the materials from which they are made. Previously, around the 15th-16th centuries, metals and wood were the main materials, a little later glass, and almost at all times porcelain and faience. But today's century is the time of polymers, which will be discussed further.

The concept of polymers

Polymer. What it is? You can answer from different points of view. On the one hand, this modern material used for the manufacture of many household and technical items.

On the other hand, it can be said that this is a specially synthesized synthetic substance obtained with predetermined properties for use in a wide range of specializations.

Each of these definitions is correct, only the first from the point of view of household, and the second - from the point of view of the chemical. Another chemical definition is the following. Polymers are compounds based on short sections of the chain of a molecule - monomers. They are repeated many times, forming a polymer macrochain. Monomers can be both organic and inorganic compounds.

Therefore, the question is: "polymer - what is it?" - requires a detailed answer and consideration of all the properties and areas of application of these substances.

Types of polymers

There are many classifications of polymers according to various features(chemical nature, heat resistance, chain structure, and so on). In the table below, we briefly review the main types of polymers.

Classification of polymers

Principle	Kinds	Definition	Examples
By origin (origin)	Natural (natural)	Those that occur naturally, in nature. Created by nature.	DNA, RNA, proteins, starch, amber, silk, cellulose, natural rubber
	Synthetic	Obtained in the laboratory by man, are not related to nature.	PVC, polyethylene, polypropylene, polyurethane and others
	artificial	Created by man in the laboratory, but based on	Celluloid, cellulose acetate, nitrocellulose
From the point of view of the chemical nature	organic nature	Most of all known polymers. Based on the monomer of organic matter (consists of C atoms, it is possible to include N, S, O, P and others atoms).	All synthetic polymers
	inorganic nature	The basis is made up of such elements as Si, Ge, O, P, S, H and others. Properties of polymers: they are not elastic, they do not form macrochains.	Polysilanes, polydichlorophosphazene, polygermanes, polysilicic acids
	organoelement nature	Blend of organic and inorganic polymers. The main chain is inorganic, the side chains are organic.	Polysiloxanes, polycarboxylates, polyorganocyclophosphazenes.
Main chain difference	Homochain	The main chain is either carbon or silicon.	Polysilanes, polystyrene, polyethylene and others.
	heterochain	The main frame is made up of different atoms.	Examples of polymers are polyamides, proteins, ethylene glycol.

Polymers of a linear, network and branched structure are also distinguished. The basis of polymers allows them to be thermoplastic or thermoset. They also have differences in their ability to deform under normal conditions.

Physical properties of polymeric materials

The main two states of aggregation characteristic of polymers are:

• amorphous;
• crystalline.

Each is characterized by its own set of properties and is of great practical importance. For example, if a polymer exists in an amorphous state, then it can be both a viscous liquid, a glassy substance, and a highly elastic compound (rubbers). It finds wide application in chemical industries, construction, engineering, production of industrial goods.

The crystalline state of the polymers is rather conditional. Actually given state interspersed with amorphous sections of the chain, and in general the whole molecule turns out to be very convenient for obtaining elastic, but at the same time high-strength and hard fibers.

Melting points for polymers are different. Many amorphous melt at room temperature, and some synthetic crystalline can withstand fairly high temperatures (plexiglass, fiberglass, polyurethane, polypropylene).

Polymers can be dyed in a variety of colors, without restrictions. Due to their structure, they are able to absorb paint and acquire the brightest and most unusual shades.

Chemical properties of polymers

The chemical properties of polymers differ from those of low molecular weight substances. This is explained by the size of the molecule, the presence of various functional groups in its composition, and the total reserve of activation energy.

In general, there are several main types of reactions characteristic of polymers:

1. Reactions to be determined by the functional group. That is, if the polymer contains an OH group, which is characteristic of alcohols, then the reactions in which they will enter will be identical to those of oxidation, reduction, dehydrogenation, and so on).
2. Interaction with NMS (low molecular weight compounds).
3. Reactions of polymers with each other with the formation of cross-linked networks of macromolecules (network polymers, branched).
4. Reactions between functional groups within one polymer macromolecule.
5. Decay of a macromolecule into monomers (chain destruction).

All of the above reactions have in practice great importance to obtain polymers with predetermined and human-friendly properties. The chemistry of polymers makes it possible to create heat-resistant, acid- and alkali-resistant materials, which at the same time have sufficient elasticity and stability.

The use of polymers in everyday life

The use of these compounds is ubiquitous. One can hardly recall areas of industry, the national economy, science and technology in which a polymer would not be needed. What is it - polymer economy and widespread use, and what is it limited to?

1. Chemical industry (production of plastics, tannins, synthesis of the most important organic compounds).
2. Mechanical engineering, aircraft building, oil refineries.
3. Medicine and pharmacology.
4. Obtaining dyes and pesticides and herbicides, agricultural insecticides.
5. Construction industry (steel alloying, sound and heat insulation structures, building materials).
6. Manufacture of toys, dishes, pipes, windows, household items and household utensils.

The chemistry of polymers makes it possible to obtain more and more new, completely universal in properties materials, which have no equal either among metals, or among wood or glass.

Examples of products made of polymeric materials

Before naming specific products made of polymers (it is impossible to list them all, their diversity is too great), first you need to figure out what a polymer gives. The material that is obtained from the Navy will be the basis for future products.

The main materials made from polymers are:

• plastics;
• polypropylenes;
• polyurethanes;
• polystyrenes;
• polyacrylates;
• phenol-formaldehyde resins;
• epoxy resins;
• caprons;
• viscose;
• nylons;
• adhesives;
• films;
• tannins and others.

This is only a small list of the variety that modern chemistry offers. Well, here it already becomes clear what objects and products are made of polymers - almost any household items, medicine and other areas ( plastic windows, pipes, dishes, tools, furniture, toys, films, etc.).

Polymers in various branches of science and technology

We have already touched on the question of the areas in which polymers are used. Examples showing their importance in science and technology can be given as follows:

• antistatic coatings;
• electromagnetic screens;
• cases of almost all household appliances;
• transistors;
• LEDs and so on.

There are no limits to the imagination on the application polymer materials in modern world.

Polymer production

Polymer. What it is? It is practically everything that surrounds us. Where are they produced?

1. Petrochemical (petroleum refining) industry.
2. Special plants for the production of polymeric materials and products from them.

These are the main bases on the basis of which polymeric materials are obtained (synthesized).

Polymers are organic and inorganic substances, which are divided into various types and views. What are polymers and how are they classified?

General characteristics of polymers

Polymers are called macromolecular substances, the molecules of which consist of repeating structural units linked to each other by chemical bonds. Polymers can be organic and inorganic, amorphous or crystalline substances. In polymers, there is always a large number of monomer units, if this amount is too small, then this is no longer a polymer, but an oligomer. The number of links is considered sufficient if the properties do not change when a new monomeric link is added.

Rice. 1. Polymer structure.

The substances from which polymers are obtained are called monomers.

Polymer molecules can have a linear, branched or three-dimensional structure. The molecular weight of conventional polymers ranges from 10,000 to 1,000,000.

The polymerization reaction is characteristic of many organic substances in which there are double or triple bonds.

For example: polyethylene formation reaction:

nCH 2 \u003d CH 2 -\u003e [-CH 2 -CH 2 -] n

where n is the number of monomer molecules interconnected during polymerization, or the degree of polymerization.

Polyethylene is produced at high temperature and high pressure. Polyethylene is chemically stable, mechanically strong and therefore widely used in the manufacture of equipment in various industries. It has high electrical insulating properties and is also used as food packaging.

Rice. 2. The substance is polyethylene.

Structural units are groups of atoms that repeat many times in a macromolecule.

Types of polymers

According to their origin, polymers can be divided into three types:

• natural. Natural or natural polymers can be found in nature under natural conditions. This group includes, for example, amber, silk, rubber, starch.

Rice. 3. Rubber.

• synthetic. Synthetic polymers are obtained in the laboratory, they are synthesized by a person. Such polymers include PVC, polyethylene, polypropylene, polyurethane. these substances have nothing to do with nature.
• artificial. Artificial polymers differ from synthetic ones in that they are synthesized, albeit under laboratory conditions, but on the basis of natural polymers. Artificial polymers include celluloid, cellulose acetate, nitrocellulose.

From the point of view of the chemical nature, polymers are divided into organic, inorganic and organoelement. Most of all known polymers are organic. These include all synthetic polymers. The basis of substances of inorganic nature are elements such as S, O, P, H and others. Such polymers are not elastic and do not form macrochains. These include polysilanes, polysilicic acids, polygermanes. Electroorganic polymers include a mixture of both organic and inorganic polymers. The main chain is always inorganic, the side chains are organic. Examples of polymers are polysiloxanes, polycarboxylates, polyorganocyclophosphazenes.

All polymers can be in different states of aggregation. They can be liquids (lubricants, varnishes, adhesives, paints), elastic materials (rubber, silicone, foam), as well as hard plastics (polyethylene, polypropylene).

Most of the modern building materials, medicines, fabrics, household items, packaging and consumables are polymers. This is a whole group of compounds that have characteristic distinguishing features. There are a lot of them, but despite this, the number of polymers continues to grow. After all, synthetic chemists annually discover more and more new substances. At the same time, it was the natural polymer that was of particular importance at all times. What are these amazing molecules? What are their properties and what are the features? We will answer these questions in the course of the article.

Polymers: general characteristics

From the point of view of chemistry, a polymer is considered to be a molecule having a huge molecular weight: from several thousand to millions of units. However, in addition to this feature, there are several more by which substances can be classified precisely as natural and synthetic polymers. This is:

• constantly repeating monomer units that are connected using different interactions;
• the degree of polymerase (i.e. the number of monomers) must be very high, otherwise the compound will be considered an oligomer;
• a certain spatial orientation of the macromolecule;
• set of important physical and chemical properties characteristic only for this group.

In general, a substance of a polymeric nature is quite easy to distinguish from others. One has only to look at his formula to understand it. A typical example is the well-known polyethylene, widely used in everyday life and industry. It is the product into which ethene or ethylene enters. Reaction in general view is written as follows:

nCH 2 \u003d CH 2 → (-CH-CH-) n, where n is the degree of polymerization of molecules, showing how many monomeric units are included in its composition.

Also, as an example, one can cite a natural polymer, which is well known to everyone, it is starch. In addition, amylopectin, cellulose, chicken protein and many other substances belong to this group of compounds.

Reactions, as a result of which macromolecules can be formed, are of two types:

• polymerization;
• polycondensation.

The difference is that in the second case, the interaction products are low molecular weight. The structure of the polymer can be different, it depends on the atoms that form it. Often there are linear forms, but there are also three-dimensional mesh, very complex.

If we talk about the forces and interactions that hold monomer units together, then we can identify several main ones:

• Van der Waals forces;
• chemical bonds (covalent, ionic);
• electrostatic interaction.

All polymers cannot be combined into one category, since they have a completely different nature, method of formation and perform different functions. Their properties also differ. Therefore, there is a classification that allows you to divide all representatives of this group of substances into different categories. It may be based on several features.

Classification of polymers

If we take as a basis the qualitative composition of the molecules, then all the substances under consideration can be divided into three groups.

1. Organic - these are those that include atoms of carbon, hydrogen, sulfur, oxygen, phosphorus, nitrogen. That is, those elements that are biogenic. Examples include a lot: polyethylene, polyvinyl chloride, polypropylene, viscose, nylon, natural polymer - protein, nucleic acids etc.
2. Elementorganic - those that include some kind of extraneous inorganic and not Most often it is silicon, aluminum or titanium. Examples of such macromolecules: glass polymers, composite materials.
3. Inorganic - the chain is based on silicon atoms, not carbon. Radicals can also be part of side branches. They were discovered quite recently, in the middle of the 20th century. Used in medicine, construction, engineering and other industries. Examples: silicone, cinnabar.

If we divide the polymers by origin, we can distinguish three groups.

1. Natural polymers, the use of which has been widely carried out since antiquity. These are such macromolecules, for the creation of which a person did not make any efforts. They are products of the reactions of nature itself. Examples: silk, wool, protein, nucleic acids, starch, cellulose, leather, cotton, and others.
2. Artificial. These are macromolecules that are created by man, but based on natural analogues. That is, the properties of an already existing natural polymer are simply improved and changed. Examples: artificial
3. Synthetic - these are polymers in the creation of which only a person participates. There are no natural analogues for them. Scientists are developing methods for the synthesis of new materials that would have improved technical specifications. This is how synthetics are born. polymer compounds different kind. Examples: polyethylene, polypropylene, rayon, etc.

There is another sign that underlies the division of the substances under consideration into groups. These are reactivity and thermal stability. There are two categories for this parameter:

• thermoplastic;
• thermosetting.

The most ancient, important and especially valuable is still a natural polymer. Its properties are unique. Therefore, we will further consider this category of macromolecules.

What substance is a natural polymer?

To answer this question, let's first look around us. What surrounds us? Living organisms around us that feed, breathe, reproduce, bloom and produce fruits and seeds. And what do they represent from a molecular point of view? These are connections such as:

• proteins;
• nucleic acids;
• polysaccharides.

So, each of the above compounds is a natural polymer. Thus, it turns out that life around us exists only due to the presence of these molecules. Since ancient times, people have used clay, building mixtures and mortars to strengthen and create a home, weave yarn from wool, and use cotton, silk, wool and animal skin to create clothes. Natural organic polymers accompanied man at all stages of his formation and development and in many ways helped him achieve the results that we have today.

Nature itself gave everything to make people's lives as comfortable as possible. Over time, rubber was discovered, its remarkable properties were clarified. Man has learned to use starch for food purposes, and cellulose for technical purposes. Camphor is also a natural polymer, which has also been known since ancient times. Resins, proteins, nucleic acids are all examples of compounds under consideration.

The structure of natural polymers

Not all representatives of this class of substances are arranged in the same way. Thus, natural and synthetic polymers can differ significantly. Their molecules are oriented in such a way that it is most beneficial and convenient to exist from an energy point of view. At the same time, many natural species are able to swell and their structure changes in the process. There are several most common options for the structure of the chain:

• linear;
• branched;
• stellate;
• flat;
• mesh;
• tape;
• comb-shaped.

Artificial and synthetic representatives of macromolecules have a very large mass, a huge number of atoms. They are created with specially specified properties. Therefore, their structure was originally planned by man. Natural polymers are most often either linear or reticulated in structure.

Examples of natural macromolecules

Natural and artificial polymers are very close to each other. After all, the first become the basis for the creation of the second. There are many examples of such transformations. Let's take a look at some of them.

1. Ordinary milky-white plastic is a product obtained by treating cellulose with nitric acid with the addition of natural camphor. The polymerization reaction causes the resulting polymer to solidify and become desired product. And the plasticizer - camphor, makes it able to soften when heated and change its shape.
2. Acetate silk, copper-ammonia fiber, viscose - all these are examples of those threads, fibers that are obtained on the basis of cellulose. Fabrics from natural cotton and linen are not so strong, not shiny, easily crumpled. But artificial analogues of these shortcomings are deprived, which makes their use very attractive.
3. Artificial stones, building materials, mixtures, leather substitutes are also examples of polymers obtained from natural raw materials.

The substance, which is a natural polymer, can also be used in its true form. There are also many such examples:

• rosin;
• amber;
• starch;
• amylopectin;
• cellulose;
• wool;
• cotton;
• silk;
• cement;
• clay;
• lime;
• proteins;
• nucleic acids and so on.

Obviously, the class of compounds we are considering is very numerous, practically important and significant for people. Now let's take a closer look at several representatives of natural polymers, which are in great demand at the present time.

Silk and wool

The formula of natural silk polymer is complex, because it chemical composition expressed by the following components:

• fibroin;
• sericin;
• waxes;
• fats.

The main protein itself, fibroin, contains several types of amino acids in its composition. If you imagine its polypeptide chain, then it will look something like this: (-NH-CH 2 -CO-NH-CH (CH 3) -CO-NH-CH 2 -CO-) n. And this is only part of it. If we imagine that an equally complex sericin protein molecule is attached to this structure with the help of van der Waals forces, and together they are mixed into a single conformation with wax and fats, then it is clear why it is difficult to depict the formula of natural silk.

Today, most of this product is supplied by China, because in its open spaces there is a natural habitat for the main producer - the silkworm. Previously, starting from the most ancient times, natural silk was highly valued. Only noble, rich people could afford clothes from it. Today, many characteristics of this fabric leave much to be desired. For example, it is highly magnetized and wrinkled, in addition, it loses its luster and fades from exposure to the sun. Therefore, artificial derivatives based on it are more in use.

Wool is also a natural polymer, as it is a waste product of the skin and sebaceous glands of animals. Based on this protein product, knitwear is made, which, like silk, is a valuable material.

Starch

The natural polymer starch is a waste product of plants. They produce it as a result of the process of photosynthesis and accumulate in different parts body. Its chemical composition:

• amylopectin;
• amylose;
• alpha glucose.

The spatial structure of starch is very branched, disordered. Thanks to the amylopectin included in the composition, it is able to swell in water, turning into a so-called paste. This one is used in engineering and industry. Medicine, food industry, manufacturing wallpaper adhesives- these are also the areas of use of this substance.

Among plants containing maximum amount starch, we can distinguish:

• corn;
• potato;
• wheat
• cassava;
• oats;
• buckwheat;
• bananas;
• sorghum.

On the basis of this biopolymer, bread is baked, pasta is made, kissels, cereals and other food products are cooked.

Cellulose

From the point of view of chemistry, this substance is a polymer, the composition of which is expressed by the formula (C 6 H 5 O 5) n. The monomeric link in the chain is beta-glucose. The main sites of cellulose content are the cell walls of plants. That is why wood is a valuable source of this compound.

Cellulose is a natural polymer that has a linear spatial structure. It is used for the production of the following types of products:

• pulp and paper products;
• artificial fur;
• different types of artificial fibers;
• cotton
• plastics;
• smokeless powder;
• filmstrip and so on.

Obviously, its industrial value is great. In order for a given compound to be used in production, it must first be extracted from plants. This is done by long-term cooking of wood in special devices. Further processing, as well as the reagents used for digestion, differ. There are several ways:

• sulfite;
• nitrate;
• soda;
• sulfate.

After such processing, the product still contains impurities. It is based on lignin and hemicellulose. To get rid of them, the mass is treated with chlorine or alkali.

In the human body, there are no such biological catalysts that would be able to break down this complex biopolymer. However, some animals (herbivores) have adapted to this. They have certain bacteria in their stomach that do it for them. In return, microorganisms receive energy for life and habitat. This form of symbiosis is extremely beneficial for both parties.

Rubber

It is a natural polymer with valuable economic importance. It was first described by Robert Cook, who discovered it in one of his travels. It happened like this. Having landed on an island inhabited by natives unknown to him, he was hospitably received by them. His attention was attracted by local children who were playing with an unusual object. This spherical body pushed off the floor and bounced high up, then returned.

Having asked the local population about what this toy was made of, Cook learned that the juice of one of the trees, the hevea, hardens in this way. Much later it was found out that this is the rubber biopolymer.

The chemical nature of this compound is known - it is isoprene that has undergone natural polymerization. Rubber formula (C 5 H 8) n. Its properties, due to which it is so highly valued, are the following:

• elasticity;
• wear resistance;
• electrical insulation;
• waterproof.

However, there are also disadvantages. In the cold, it becomes brittle and brittle, and in the heat, it becomes sticky and viscous. That is why it became necessary to synthesize analogues of an artificial or synthetic base. Today, rubbers are widely used for technical and industrial purposes. The most important products based on them:

• rubber;
• ebonites.

Amber

It is a natural polymer, because in its structure it is a resin, its fossil form. The spatial structure is a frame amorphous polymer. It is very flammable and can be ignited with a match flame. It has luminescence properties. This is a very important and valuable quality that is used in jewelry. Jewelry based on amber is very beautiful and in demand.

In addition, this biopolymer is also used for medical purposes. It is made from it sandpaper, varnish coatings for various surfaces.

Polymeric materials (plastics, plastics) are, as a rule, hardened composite compositions in which polymers and oligomers serve as a binder. They received the widespread name “plastics” (which is not entirely correct) because they are in a plastic (fluid) state when processed into products. Therefore, scientifically substantiated names are "polymeric materials", "composite materials based on polymers".

Polymers (from the Greek poly - many, meres - parts) are high molecular weight chemical compounds, whose molecules consist of a huge number of multiply repeating elementary units of the same structure. Such molecules are called macromolecules. Depending on the arrangement of atoms and atomic groups (elementary units) in them, they can have a linear (chain-like), branched, network and spatial (three-dimensional) structure, which determines their physical and mechanical and Chemical properties. The formation of these molecules is possible due to the fact that carbon atoms are easily and firmly connected to each other and to many other atoms.

There are also prepolymers (prepolymers, prepolymers), which are compounds containing functional groups and capable of participating in the reactions of growth or crosslinking of the polymer chain with the formation of high-molecular linear and network polymers. First of all, these are also liquid polyol products with an excess of polyisocyanates or other compounds in the production of polyurethane products.

By origin, polymers can be natural, artificial and synthetic.

Natural polymers are mainly biopolymers - protein substances, starch, natural resins (pine rosin), cellulose, natural rubber, bitumen, etc. Many of them are formed during biosynthesis in living cells and plant organisms. However, in industry, in most cases, artificial and synthetic polymers are used.

The main raw materials for the production of polymers are by-products of the coal and oil industries, fertilizer production, natural gas, cellulose and other substances. The process of formation of such macromolecules and the polymer as a whole is caused by exposure to the initial substance (monomer) of a stream of light rays, electric discharges of currents high frequency, heating, pressure, etc.

Depending on the method of obtaining polymers, they can be divided into polymerization, polycondensation and modified natural polymers. The process of obtaining polymers by successively attaching monomer units to each other as a result of the opening of multiple (unsaturated) bonds is called the polymerization reaction. During this reaction, a substance can change from a gaseous or liquid state to a very thick liquid or solid state. The reaction is not accompanied by the separation of any low molecular weight side products. Both the monomer and the polymer are characterized by the same elemental composition. The polymerization reaction produces polyethylene from ethylene, polypropylene from propylene, polyisobutylene from isobutylene and many other polymers.

During the polycondensation reaction, the atoms of two or more monomers are rearranged and low molecular weight side products (for example, water, alcohols, or other low molecular weight substances) are released from the reaction sphere. The polycondensation reaction produces polyamides, polyesters, epoxy, phenol-formaldehyde, organosilicon and other synthetic polymers, also called resins.

Depending on the relationship to heat and solvents, polymers, as well as materials based on them, are divided into thermoplastic and thermosetting.

Thermoplastic polymers(thermoplastics), when processed into products, can repeatedly pass from a solid state of aggregation to a viscous-fluid state (melt), and solidify again when cooled. They usually have no high temperature transition to a viscous-fluid state, are well processed by injection molding, extrusion and pressing. The shaping of products from them is a physical process, which consists in the solidification of a liquid or softened material during its cooling and no chemical changes occur. Most of the thermoplastics are also capable of dissolving in appropriate solvents. Thermoplastic polymers have a linear or slightly branched macromolecular structure. These include certain types of polyethylene, polyvinyl chloride, fluoroplastics, polyurethanes, bitumen, etc.

Thermosets (thermosets) include polymers, the processing into products of which is accompanied by chemical reaction the formation of a network or three-dimensional polymer (by curing, cross-linking of chains) and the transition from a liquid to a solid state occurs irreversibly. Their cured state is thermally stable, and they lose the ability to re-transition into a viscous-fluid state (for example, phenolic, polyester, epoxy polymers, etc.).

Classification and properties of polymeric materials

Polymeric materials, depending on the composition or number of components, are divided into unfilled, represented by only one binder (polymer) - organic glass, in most cases polyethylene film; filled, which, to obtain the required set of properties, may include fillers, plasticizers, stabilizers, hardeners, pigments - fiberglass, textolite, linoleum and gas-filled (foam and foam plastics) - expanded polystyrene, polyurethane foam, etc.

Depending on the physical condition normal temperature and viscoelastic properties, polymeric materials are rigid, semi-rigid, soft and elastic.

Rigid - these are solid, elastic materials of an amorphous structure, having an elastic modulus of more than 1000 MPa. They are brittle with little elongation at break. These include phenolic plastics, aminoplasts, plastics based on glyptal and other polymers.

The density of polymeric materials is most often in the range of 900-1800 kg/m3, i.e. they are 2 times lighter than aluminum and 5.6 times lighter than steel. At the same time, the density of porous polymeric materials (foam plastics) can be 30..15 kg/m3, and dense - more than 2,000 kg/m3.

The compressive strength of polymeric materials in most cases exceeds many traditional building materials (concrete, brick, wood) and is about 70 MPa for unfilled polymers, more than 200 MPa for reinforced plastics, 100-150 MPa for tensile materials with powdered filler, for glass fiber materials - 276.414 MPa and more.

The thermal conductivity of such materials depends on their porosity and production technology. For foam and foam plastics, it is 0.03.0.04 W / m-K, for the rest - 0.2.0.7 W / mK, or 500.600 times lower than for metals.

The disadvantage of many polymeric materials is their low heat resistance. For example, most of them (based on polystyrene, polyvinyl chloride, polyethylene and other polymers) have a heat resistance of 60.80 °C. On the basis of phenol-formaldehyde resins, heat resistance can reach 200 °C, and only on organosilicon polymers - 350 °C.

Being hydrocarbon compounds, many polymeric materials are combustible or have low fire resistance. Products based on polyethylene, polystyrene, cellulose derivatives are flammable and combustible with abundant soot emission. Hardly combustible are products based on polyvinyl chloride, polyester fiberglass, phenolic plastics, which only char at elevated temperatures. Non-combustible are polymeric materials with a high content of chlorine, fluorine or silicon.

Many polymeric materials, when processed, burned, and even heated, release substances hazardous to health, such as carbon monoxide, phenol, formaldehyde, phosgene, hydrochloric acid etc. Their significant disadvantage is also a high coefficient of thermal expansion - from 2 to 10 times higher than that of steel.

Polymeric materials are characterized by shrinkage during solidification, reaching 5.8%. Most of them have a low modulus of elasticity, much lower than that of metals. Under prolonged loads, they have high creep. As the temperature rises, creep increases even more, which leads to undesirable deformations.

The development of modern technologies has led to the emergence of materials that have exceptional performance. Polymeric materials may have molecular weight from several thousand to several million. The main qualities of such materials determine their wide distribution. Every year, polymers account for an increasing number of manufactured products. That is why we will consider their features in more detail.

Polymer properties

The use of polymers is very extensive. This is due to the special qualities that the material in question possesses. Today, polymeric materials are found in a wide variety of areas, are present in almost every home. The process of production of polymeric materials is constantly being improved, the composition is being changed, due to which it acquires new operational qualities.

The physical properties of polymers can be characterized as follows:

1. Low coefficient of thermal conductivity. That is why some polymers can be used as insulation for some jobs.
2. The high TCLE is due to the relatively high mobility of the bonds and the constant change in the deformation coefficient.
3. Despite the high CLTE, polymeric materials are ideal for sputtering. AT recent times often you can find a situation where the polymer is applied to the surface in the form of a thin layer to give the metal and other materials anti-corrosion qualities. Modern application technologies make it possible to obtain a thin protective film.
4. The specific gravity can vary over a fairly large range depending on the characteristics of a particular composition.
5. The rather high tensile strength is partly due to increased ductility. Of course, the indicator is significantly inferior to those that the metal or alloys have.
6. The strength of polymers is relatively low. In order to increase the value of impact strength, various additional components are added to the composition, due to which special types of polymers are obtained.
7. Consideration should be given to the low operating temperature. Polymeric materials do not cope well with heat. That is why many versions can operate at temperatures not exceeding 80 degrees Celsius. If the recommended temperature threshold is exceeded, then there is a possibility that strong heating will cause an increase in the plasticity of the polymer material. Too high plasticity causes a decrease in strength and a change in other physical properties.
8. Resistivity can vary over a fairly large range. An example of such polymers is PVC hard, which has 10 17 ohm×cm.
9. Many polymeric materials have increased flammability. This moment determines that polymers cannot be used in some industries. In addition, the chemical composition determines that during combustion, toxic substances or acrid smoke can be released.
10. When using a special production technology, the surface may have a reduced coefficient of friction against steel. Due to this, the coating lasts much longer, and defects do not appear on it.
11. The coefficient of linear expansion is from 70 to 200 10 -6 per degree Celsius.

Considering the characteristics of common polymers, do not forget about the following qualities:

1. Good dielectric properties allow the use of polymeric material without fear of electric shock. That is why polymers are often used in the creation of tools and equipment designed to work with electricity.
2. Linear polymers are able to restore their original shape after prolonged exposure to stress. An example is the effect of a transverse load, which bends a part, but after it disappears, the shape is not preserved.
3. An important quality of all polymers is a significant change in performance when a small amount of impurities is introduced.
4. Today, polymeric materials are found in a wide variety of aggregate states. An example is glue, grease, sealant, paints, some solid polymeric materials. Solid plastics, which are used in the manufacture of a wide variety of equipment, have become widespread. As previously noted, the substance has a high elasticity, due to which silicone, rubber, foam rubber and other similar polymeric materials were obtained.

It should be borne in mind that the chemical composition of polymeric materials can vary significantly. GOST presents a procedure for qualitative assessment, which is based on points.

Polymeric materials are widely used in industry, as they have an increased resistance to inorganic reagents. That is why they are used in the production of tanks for clean water or high-purity reagents.

All of the above information determines that polymers have become simply widespread in a wide variety of industries. However, do not forget that there are several dozen basic types of polymeric materials, all of which have their own specific qualities. That is why it is necessary to consider in detail the classification of polymeric materials.

Classification of polymers

There are a fairly large number of indicators by which synthetic polymeric materials can be classified. At the same time, the classification also affects the main operational qualities. That is why we consider the varieties of polymeric materials in more detail.

Classification is carried out according to the state of aggregation:

1. Solid. Almost all people are familiar with polymers, as they are used in the manufacture of housings for household appliances and other household items. Another name for this material is plastic. In solid form, the polymeric material has sufficiently high strength and ductility.
2. Elastic materials. The high elasticity of the structure has been used in the production of rubber, foam rubber, silicone and other similar materials. Most of it is found in construction as insulation, which is also associated with basic performance.
3. Liquids. On the basis of polymers, a fairly large number of various liquid substances are produced, most of which are also applicable in construction. An example is paints, varnishes, sealants and much more.

Liquid polymers - paints
Elastic polymers - rubber coating

Different kinds polymer materials have different performance characteristics. That is why their features should be considered. There are commercially available polymers that are in liquid state, but after entering the reaction become solid.

Classification of polymers by origin:

1. Artificial substances characterized by high molecular weight.
2. Biopolymers, which are also called natural.
3. Synthetic.

Polymeric materials of synthetic origin have become more widespread, since exceptional performance is achieved by mixing a wide variety of substances. Artificial polymers are found in almost every home today.

Classification synthetic materials is also carried out according to the features of the molecular network:

1. Linear.
2. Branched.
3. Spatial.

Classification is also carried out according to the nature of the heteroatom:

1. The main chain may include an oxygen atom. Such a chain structure makes it possible to obtain complex and simple polyesters and peroxides.
2. IUDs, which are characterized by the presence of a sulfur atom in the main chain. Due to this structure, polythioethers are obtained.
3. You can also find compounds in the main chain of which there are phosphorus atoms.
4. The main chain can include both oxygen and nitrogen atoms. The most common example of such a structure can be called polyurethanes.
5. Polyamines and polyamides are prominent representatives of polymeric materials that have nitrogen atoms in their main chain.

In addition, there are two large groups of polymeric materials:

1. Carbochain - a variant that has the main chain of the HMC macromolecule with one carbon atom.
2. Heterochain - a structure that, in addition to the carbon atom, also has atoms of other substances.

There are simply a huge number of varieties of carbon chain polymers:

1. High molecular weight compounds called Teflon.
2. polymeric alcohols.
3. Structures with saturated main chains.
4. Chains with saturated basic bonds, which are represented by polyethylene and polypropylene. Note that today these types of polymers are simply very widespread, they are used in the production of building materials and other things.
5. Naval Forces, which are obtained on the basis of the processing of alcohols.
6. Substances derived from the processing of carboxylic acid.
7. Substances derived from nitriles.
8. Materials that were obtained on the basis of aromatic hydrocarbons. The most common representative of this group is polystyrene. It has been widely used due to its high insulating qualities. Today, polystyrene is used to insulate residential and non-residential premises, Vehicle and other technology.

All the above information determines that there is simply a huge number of varieties of polymeric materials. This moment also determines their wide distribution, application in almost all industries and fields of human activity.

Application of polymers

The modern economy and people's lives simply cannot do without polymeric materials. This is due to the fact that they have a relatively low cost, if necessary, the main performance can be changed for specific tasks.

Application of polymeric materials

Considering the use of polymers, attention should be paid to the following points:

1. Active production began at the beginning of the 20th century. Initially, the production technology consisted in the processing of low-molecular raw materials and cellulose. As a result of their processing, paints and films appeared.
2. Modern polymers have influenced the development of all industries. At the time of the development of cinema, the appearance of transparent films made it possible to shoot the first pictures.
3. In the modern world, the considered polymeric materials are used in almost all industries. An example is the use of polymers in the production of toys, equipment, medicines, fabrics, building materials and much more. In addition, they become part of other materials to change their basic performance, they are used in the processing of natural leather or rubber. Through the use of plastic, manufacturers have been able to reduce the cost of computers and mobile devices, making them lighter and thinner. If we compare metal and polymers, then the difference in cost can be simply huge.
4. Improvement in the technology for the production of polymeric materials has led to the emergence of more modern composites, which have been used in mechanical engineering and many other industries.
5. The use of the polymer is also associated with space. The creation of both aircraft and various satellites can be cited as an example. A significant reduction in mass allows you to overcome the earth's gravity at a lower cost. In addition, polymers are well known for being able to withstand environmental stresses such as temperature and humidity fluctuations.

Initially, low-quality low-molecular substances were used as raw materials in the production of polymers. That is why they had a huge number of shortcomings. However, the improvement of production technologies has led to the fact that today polymers have high safety in use, do not emit harmful substances in environment. Therefore, they have become increasingly used in the manufacture of things used in everyday life.

In conclusion, we note that the area under consideration is constantly developing, due to which composite materials. They are much more expensive than polymers, but they have exceptional physical, chemical and mechanical properties. In the near future, polymeric materials will continue to be actively used in a wide variety of fields, since there are no alternatives to replace them yet.