Types of polymeric materials. What are polymers and plastics

Imagine the following situation. You leave the store and hurry to throw the bag into the car as soon as possible. It is done. You quickly check your phone and get behind the wheel. When you enter your apartment, you wipe your feet on a rubber mat, take everything out of the bags: a non-stick frying pan, toys for the child, shaving foam, a couple of shirts, wallpaper. It seems like they didn't forget anything. You take a bottle of water with you and go to the computer - it's time to work. Everything mentioned above contains polymers. Up to the store.

Polymers - what is it?

Polymers are materials made up of long, repeating chains of molecules. They possess unique properties depending on the type of molecules being connected and how they are connected. Some of them bend and stretch, such as rubber and polyester. Others are hard and tough, like epoxies and organic glass.

The term "polymer" is commonly used to describe plastics, which are synthetic polymers. Be that as it may, natural polymers also exist: rubber and wood, for example, are natural polymers composed of a simple hydrocarbon, isoprene. Proteins are also natural polymers, they are made up of amino acids. Nucleic acids (DNA and RNA) are polymers of nucleotides - complex molecules consisting of a nitrogen-containing base, sugar and phosphoric acid.

Who thought of this before?

Hermann Staudinger, a lecturer in organic chemistry at the ETH Zurich, is considered the father of polymers.

Hermann Staudinger. Source: Wikimedia

His research in the 1920s paved the way for future work with both natural and synthetic polymers. He introduced two terms that are key to understanding polymers: polymerization and macromolecule. In 1953, Staudinger received the well-deserved Nobel Prize "for his discoveries in the field of macromolecular chemistry."

Polymerization is a method of creating synthetic polymers by combining smaller molecules, monomers, into a chain held together by covalent bonds. Various chemical reactions, such as those caused by heat and pressure, change the chemical bonds that hold monomers together. The process causes molecules to bond in a linear, branched, or three-dimensional pattern, turning them into polymers. These chains of monomers are also called macromolecules. One macromolecule can consist of hundreds of thousands of monomers.

Types of polymers

The type of polymer depends on its structure. From the above, we understand that there should be three such types.

linear polymers. These are compounds in which the monomers are chemically inert with respect to each other and are connected only by van der Waals forces (forces of intermolecular (and interatomic) interaction with an energy of 10–20 kJ / mol. - Note. ed.). The term "linear" does not at all mean a rectilinear arrangement of molecules relative to each other. On the contrary, they are more characterized by a serrated or helical configuration, which gives such polymers mechanical strength.

branched polymers. They are formed by chains with side branches (the number of branches and their length are different). Branched polymers are stronger than linear ones.

Linear and branched polymers soften when heated and re-solidify when cooled. This property is called thermoplasticity, and the polymers themselves are called thermoplastic, or thermoplastics. Bonds between molecules in such polymers can be broken and reconnected. It means that plastic bottles can be used to produce other polymer-containing items, from rugs to fleece jackets. Of course, you can make more bottles. All that is needed for processing is high temperature. Thermoplastic polymers can not only be melted, but also dissolved, since van der Waals bonds are easily torn under the action of reagents. Thermoplastics include polyvinyl chloride, polyethylene, polystyrene, etc.

If the macromolecules contain reactive monomers, then when heated, they are connected by many cross-links, and the polymer acquires a spatial structure. Such polymers are called thermosetting or thermoplastics.

On the one hand, thermosets have positive qualities: they are harder and heat resistant. On the other hand, after the bonds between the molecules of thermosetting polymers are broken, it cannot be established a second time. Recycling in this case disappears, and this is very bad. The most common polymers in this group are polyester, vinylester and epoxides.

Materials based on polymers. Polymers are used to produce fibers, films, rubbers, varnishes, adhesives, plastics and composite materials(composites).

Fibers are obtained by forcing polymer solutions or melts through thin holes (dies) in a plate, followed by solidification. Fiber-forming polymers include polyamides, polyacrylonitriles, etc.

Polymer films are obtained from polymer melts by extrusion through dies with slotted holes or by applying polymer solutions to a moving tape or by calendering "polymers. Films are used as an electrical insulating and packaging material, the basis of magnetic tapes, etc.

Varnishes - solutions of film-forming substances in organic solvents. In addition to polymers, varnishes contain substances that increase plasticity (plasticizers), soluble dyes, hardeners, etc. They are used for electrical insulating coatings, as well as as the basis of a primer and paint and varnish enamels.

Adhesives - compositions capable of connecting various materials due to the formation of strong bonds between their surfaces and the adhesive layer. Synthetic organic adhesives are based on monomers, oligomers, polymers or mixtures thereof. The composition includes hardeners, fillers, plasticizers, etc.

Adhesives are divided into thermoplastic, thermoset and rubber. Thermoplastic adhesives bond to a surface by solidifying when cooled from pour point to room temperature or by evaporating the solvent. Thermosetting adhesives form a bond with the surface as a result of hardening (formation of cross-links), rubber adhesives - as a result of vulcanization.

Phenol- and urea-formaldehyde and epoxy resins, polyurethanes, polyesters and other polymers, thermoplastic adhesives - polyacrylics, polyamides, polyvinyl acetals, polyvinyl chloride and other polymers. The strength of the adhesive layer, for example, phenol-formaldehyde adhesives (BF, VK) at 20 ° C during shear lies in the range of 15 to 20 MPa, epoxy - up to 36 MPa.

Plastics are materials containing a polymer, which is in a viscous state during the formation of a product, and in a glassy state during its operation. All plastics are divided into thermoplastics and thermoplastics. During the molding of thermosets, irreversible reaction hardening, which consists in the formation of a mesh structure. Thermosets include materials based on phenol-formaldehyde, urea-formaldehyde, epoxy and other resins. Thermoplastics are capable of repeatedly passing into a viscous state when heated and a glassy state when cooled. Thermoplastics include materials based on polyethylene, polytetrafluoroethylene, polypropylene, polyvinyl chloride, polystyrene, polyamides and other polymers.

In addition to polymers, plastics include plasticizers, dyes and fillers. Plasticizers, such as dioctyl phthalate, dibutyl sebacate, chlorinated paraffin, reduce the glass transition temperature and increase the fluidity of the polymer. Antioxidants slow down the degradation of polymers. Fillers improve the physical and mechanical properties of polymers. Powders (graphite, soot, chalk, metal, etc.), paper, fabric are used as fillers. Composites constitute a special group of plastics.

Composite materials (composites) - consist of a base (organic, polymeric, carbon, metal, ceramic), reinforced with a filler, in the form of high-strength fibers or whiskers. Synthetic resins (alkyd, phenol-formaldehyde, epoxy, etc.) and polymers (polyamides, fluoroplasts, silicones, etc.) are used as a base.

Reinforcing fibers and crystals can be metallic, polymeric, inorganic (eg glass, carbide, nitride, boron). Reinforcing fillers largely determine the mechanical, thermal and electrical properties of polymers. Many composite polymer materials are as strong as metals. Composites based on polymers, fiberglass reinforced(fiberglass), have high mechanical strength (tensile strength 1300-2500 MPa) and good electrical insulating properties. Composites based on polymers reinforced with carbon fibers (CFRP) combine high strength and vibration resistance with increased thermal conductivity and chemical resistance. Boroplasts (fillers - boron fibers) have high strength, hardness and low creep.

Polymer-based composites are used as structural, electrical and thermal insulation, corrosion-resistant, anti-friction materials in the automotive, machine tool, electrical, aviation, radio engineering, mining, space technology, chemical engineering and construction industries.

Redoxites. Redox polymers (with redox groups or redoxionites) have received wide application.

The use of polymers. A large number of different polymers are currently widely used. The physical and chemical properties of some thermoplastics are given in Table. 14.2 and 14.3.

Polyethylene [-CH2-CH2-]n is a thermoplastic obtained by radical polymerization at temperatures up to 320 °C and pressure 120-320 MPa (polyethylene high pressure) or at pressures up to 5 MPa using complex catalysts (polyethylene low pressure). Low density polyethylene has higher strength, density, elasticity and softening point than high pressure polyethylene. Polyethylene is chemically resistant in many environments, but ages under the action of oxidizing agents (Table 14.3). A good dielectric (see table. 14.2), can be operated within temperatures from -20 to +100 ° C. Irradiation can increase the heat resistance of the polymer. Pipes, electrical products, parts of radio equipment, insulating films and cable sheaths (high-frequency, telephone, power), films, packaging material, substitutes for glass containers are made from polyethylene.

Polypropylene [-CH(CH3)-CH2-]n is a crystalline thermoplastic obtained by stereospecific polymerization. It has higher heat resistance (up to 120-140 °C) than polyethylene. It has high mechanical strength (see Table 14.2), resistance to repeated bending and abrasion, and is elastic. It is used for the manufacture of pipes, films, storage tanks, etc.

Thermoplastic obtained by radical polymerization of styrene.

The polymer is resistant to oxidizing agents, but unstable to strong acids, it dissolves in aromatic solvents (see Table 14.3).

Table 14.2. Physical Properties some polymers

* Melting temperature.

Table 14.3 Chemical properties of some polymers

Polystyrene has high mechanical strength and dielectric properties (see Table 14.2) and is used as a high-quality electrical insulating, as well as structural and decorative finishing material in instrument making, electrical engineering, radio engineering, household appliances. Flexible elastic polystyrene, obtained by drawing in a hot state, is used for sheaths of cables and wires. Foam plastics are also produced on the basis of polystyrene.

Polyvinyl chloride [-CH2-CHCl-] n is a thermoplastic produced by polymerization of vinyl chloride, resistant to acids, alkalis and oxidizing agents (see Table 14.3). Soluble in cyclohexanone, tetrahydrofuran, limited in benzene and acetone. Slow-burning, mechanically strong (see table. 14.2). The dielectric properties are worse than those of polyethylene. It is used as an insulating material that can be joined by welding. Gramophone records, raincoats, pipes and other items are made from it.

Polytetrafluoroethylene (fluoroplastic) [-CF2-CF2-]n is a thermoplastic obtained by radical polymerization of tetrafluoroethylene. It has exceptional chemical resistance to acids, alkalis and oxidizing agents. Excellent dielectric. It has very wide operating temperature limits (from -270 to +260 °С). At 400 °C, it decomposes with the release of fluorine and is not wetted by water. Fluoroplast is used as a chemically resistant structural material in the chemical industry. As the best dielectric, it is used in conditions where a combination of electrical insulating properties with chemical resistance is required. In addition, it is used for applying anti-friction, hydrophobic and protective coatings, pan coatings.

Polymethyl methacrylate (Plexiglas)

Thermoplastic obtained by polymerization of methyl methacrylate. Mechanically strong (see table. 14.2), resistant to acids, weather resistant. Soluble in dichloroethane aromatic hydrocarbons, ketones, esters. Colorless and optically clear. It is used in electrical engineering as a structural material, as well as the basis of adhesives.

Polyamides - thermoplastics containing the amido group -NHCO- in the main chain, for example poly-e-capron [-NH-(CH2)5-CO-] n, polyhexamethylene adipamide (nylon) [-NH-(CH2) 5-NH-CO- (CH2)4-CO-]n, polydodecanamide [-NH-(CH2)11-CO-]n, etc. They are obtained both by polycondensation and polymerization. The density of polymers is 1.0¸1.3 g/cm3. They are characterized by high strength, wear resistance, dielectric properties. Resistant to oils, gasoline, dilute acids and concentrated alkalis. They are used to obtain fibers, insulating films, structural, anti-friction and electrical insulating products.

Polyurethanes are thermoplastics containing -NH (CO) O - groups in the main chain, as well as ether, carbamate, etc. They are obtained by the interaction of isocyanates (compounds containing one or more NCO groups) with polyalcohols, for example, with glycols and glycerin. Resistant to dilute mineral acids and alkalis, oils and aliphatic hydrocarbons.

They are produced in the form of polyurethane foams (foam rubber), elastomers, are included in the composition of varnishes, adhesives, sealants. They are used for thermal and electrical insulation, as filters and packaging material, for the manufacture of shoes, artificial leather, rubber products. Polyesters - polymers with general formula HO [-R-O-] nH or [-OC-R-COO-R "-O-] n. Obtained either by polymerization of cyclic oxides, for example ethylene oxide, lactones (esters of hydroxy acids), or by polycondensation of glycols, diesters and other compounds Aliphatic polyesters are resistant to the action of alkali solutions, aromatic polyesters are also resistant to the action of solutions of mineral acids and salts.

They are used in the production of fibers, varnishes and enamels, films, coagulants and flotation agents, components of hydraulic fluids, etc.

Synthetic rubbers (elastomers) are obtained by emulsion or stereospecific polymerization. When vulcanized, they turn into rubber, which is characterized by high elasticity. The industry produces a large number of different synthetic rubbers (SR), the properties of which depend on the type of monomers. Many rubbers are produced by the copolymerization of two or more monomers. Distinguish SC general and special purpose. K SC general purpose include butadiene [-CH2-CH=CH-CH2-]n and styrene-butadiene [-CH2-CH=CH-CH2-]n-[-CH2-CH(C6H5)-]n. Rubbers based on them are used in mass products (tires, protective sheaths of cables and wires, tapes, etc.). Ebonite, which is widely used in electrical engineering, is also obtained from these rubbers. Rubbers obtained from SC for special purposes, in addition to elasticity, are characterized by some special properties, for example, benzo- and oil resistance (butadiene SC [-CH2-CH=CH-CH2-]n-[-CH2-CH(CN)-]n), benzo -, oil and heat resistance, incombustibility (chloroprene SC [-CH2-C (Cl) \u003d CH-CH2-] n), wear resistance (polyurethane, etc.), heat, light, ozone resistance (butyl rubber) [-C ( CH3)2-CH2-]n -[-CH2C(CH3)=CH-CH2-]m.

The most used are styrene-butadiene (more than 40%), butadiene (13%), isoprene (7%), chloroprene (5%) rubbers and butyl rubber (5%). The main share of rubber (60-70%) goes to the production of tires, about 4% - to the manufacture of shoes.

Organosilicon polymers (silicones) - contain silicon atoms in the elementary units of macromolecules, for example:

A great contribution to the development of organosilicon polymers was made by the Russian scientist K.A. Andrianov. characteristic feature of these polymers is a high heat and frost resistance, elasticity. Silicones are not alkali resistant and dissolve in many aromatic and aliphatic solvents (see Table 14.3). Silicone polymers are used to produce varnishes, adhesives, plastics and rubber. Organosilicon rubbers [-Si(R2)-O-]n, for example, dimethylsiloxane and methyl vinylsiloxane have a density of 0.96-0.98 g/cm3, a glass transition temperature of 130°C. Soluble in hydrocarbons, halocarbons, ethers. Vulcanized with organic peroxides. Rubbers can be used at temperatures from -90 to +300°C, they have weather resistance, high electrical insulating properties (r = 1015-1016 Ohm×cm). They are used for products operating under conditions of a large temperature difference, for example, for protective coatings of spacecraft, etc.

Phenolic and amino-formaldehyde resins are obtained by polycondensation of formaldehyde with phenol or amines (see §14.2). These are thermoset polymers, which, as a result of cross-linking, form a network spatial structure that cannot be converted into linear structure, i.e. the process is irreversible. They are used as the basis for adhesives, varnishes, ion exchangers, and plastics.

Plastics based on phenol-formaldehyde resins are called phenolic plastics, based on urea-formaldehyde resins - amino plastics. Phenoplasts and aminoplasts are filled with paper or cardboard (getinaks), fabric (textolite), wood, quartz and mica flour, etc. Phenoplasts are resistant to water, acid solutions, salts and bases, organic solvents, slow-burning, weather-resistant and are good dielectrics. Used in production printed circuit boards, housings for electrical and radio engineering products, foil dielectrics. Aminoplasts are characterized by high dielectric and physical-mechanical properties, are resistant to light and UV rays, slow-burning, resistant to weak acids and bases and many solvents. They can be dyed any color. They are used for the manufacture of electrical products (cases of instrumentation

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 with different points vision. On the one hand, it is a 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 criteria (chemical nature, heat resistance, chain structure, and so on). In the table below, we briefly review the main types of polymers.

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

Main two state 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, industrial goods manufacturing.

The crystalline state of the polymers are rather conditional. In fact, this state is 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 the most different colors, with no 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. Few areas of industry can be recalled, National economy, science and technology, which would not need a polymer. 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).

The author of this article is Academician Viktor Aleksandrovich Kabanov, an outstanding scientist in the field of macromolecular chemistry, a student and successor of Academician V.A. Kargin, one of the world leaders in polymer science, the creator of a large scientific school, author a large number works, books and manuals.

Polymers (from the Greek polymeres - consisting of many parts, diverse) are chemical compounds with a high molecular weight (from several thousand to many millions), the molecules of which (macromolecules) consist of a large number repeating groupings (monomeric units). The atoms that make up the macromolecules are connected to each other by the forces of the main and (or) coordination valences.

Classification of polymers

By origin, polymers are divided into natural (biopolymers), such as proteins, nucleic acids, natural resins, and synthetic, such as polyethylene, polypropylene, phenol-formaldehyde resins.

Atoms or atomic groups can be arranged in a macromolecule in the form:

• an open chain or a sequence of cycles stretched in a line (linear polymers, such as natural rubber);
• branched chains (branched polymers, eg amylopectin);
• 3D mesh (cross-linked polymers, such as cured epoxy resins).

Polymers whose molecules consist of identical monomer units are called homopolymers, for example polyvinyl chloride, polycaproamide, cellulose.

Macromolecules of the same chemical composition can be built from units of different spatial configurations. If macromolecules consist of the same stereoisomers or of different stereoisomers alternating in a chain at a certain frequency, the polymers are called stereoregular (see Stereoregular polymers).

What are copolymers
Polymers whose macromolecules contain several types of monomer units are called copolymers. Copolymers in which links of each type form sufficiently long continuous sequences that replace each other within the macromolecule are called block copolymers. To the internal (non-terminal) links of the macromolecule of one chemical structure one or more circuits of a different structure may be attached. Such copolymers are called graft copolymers (see also Copolymers).

Polymers in which each or some of the stereoisomers of the link form sufficiently long continuous sequences that replace each other within one macromolecule are called stereoblock copolymers.

Heterochain and homochain polymers

Depending on the composition of the main (main) chain, polymers are divided into: heterochain, the main chain of which contains atoms various elements, most often carbon, nitrogen, silicon, phosphorus, and homochain, the main chains of which are built from identical atoms. Of the homochain polymers, the most common are carbon chain polymers, the main chains of which consist only of carbon atoms, for example, polyethylene, polymethyl methacrylate, polytetrafluoroethylene. Examples of heterochain polymers. - polyesters (polyethylene terephthalate, polycarbonates, etc.), polyamides, urea-formaldehyde resins, proteins, some organosilicon polymers. polymers whose macromolecules, along with hydrocarbon groups, contain atoms of inorganic elements are called organoelement polymers (see Organoelement polymers). a separate group of polymers. form inorganic polymers, such as plastic sulfur, polyphosphonitrile chloride (see Inorganic polymers).

Properties and key characteristics of polymers

Linear polymers have a specific complex and . The most important of these properties are: the ability to form high-strength anisotropic highly oriented fibers and films; the ability to large, long-term developing reversible deformations; the ability to swell in a highly elastic state before dissolution; high viscosity solutions (see Polymer Solutions, Swelling). This set of properties is due to the high molecular weight, chain structure, and flexibility of macromolecules. With the transition from linear chains to branched, sparse three-dimensional networks and, finally, to dense network structures, this set of properties becomes less and less pronounced. Highly cross-linked polymers are insoluble, infusible and incapable of highly elastic deformations.

Polymers can exist in crystalline and amorphous states. Necessary condition crystallization - the regularity of sufficiently long sections of the macromolecule. in crystalline polymers. the appearance of various supramolecular structures (fibrils, spherulites, single crystals, etc.) is possible, the type of which largely determines the properties of the polymer material. Supramolecular structures in non-crystallized (amorphous) polymers are less pronounced than in crystalline ones.

Non-crystallized polymers can be in three physical states: glassy, ​​highly elastic and viscous. polymers with a low (below room) transition temperature from a glassy to a highly elastic state are called elastomers, and those with a high temperature are called plastics. Depending on the chemical composition, structure and relative position macromolecules properties of polymers. can vary over a very wide range. So, 1,4-cis-polybutadiene, built from flexible hydrocarbon chains, at a temperature of about 20 degrees C is an elastic material, which at a temperature of -60 degrees C goes into a glassy state; polymethyl methacrylate, built from more rigid chains, at a temperature of about 20 degrees C is a solid glassy product that passes into a highly elastic state only at 100 degrees C.

Cellulose, a polymer with very rigid chains connected by intermolecular hydrogen bonds, cannot exist at all in a highly elastic state up to the temperature of its decomposition. Large differences in the properties of P. can be observed even if the differences in the structure of macromolecules are at first glance small. So, stereoregular polystyrene is a crystalline substance with a melting point of about 235 degrees C, and non-stereoregular (atactic) is not able to crystallize at all and softens at a temperature of about 80 degrees C.

Polymers can enter into the following main types of reactions: the formation of chemical bonds between macromolecules (the so-called crosslinking), for example, during the vulcanization of rubbers, leather tanning; the breakdown of macromolecules into separate, shorter fragments (see Degradation of polymers); reactions of side functional groups of polymers. with low molecular weight substances that do not affect the main chain (the so-called polymer-analogous transformations); intramolecular reactions occurring between functional groups of one macromolecule, for example, intramolecular cyclization. Cross-linking often proceeds simultaneously with degradation. An example of polymer-analogous transformations is the saponification of polyvinyl acetate, leading to the formation of polyvinyl alcohol.

The rate of polymer reactions. with low molecular weight substances is often limited by the rate of diffusion of the latter into the polymer phase. This is most clearly manifested in the case of cross-linked polymers. The rate of interaction of macromolecules with low molecular weight substances often depends significantly on the nature and location of neighboring units relative to the reacting unit. The same applies to intramolecular reactions between functional groups belonging to the same chain.

Some properties of polymers, such as solubility, viscous flow, stability, are very sensitive to action. small quantities impurities or additives that react with macromolecules. So, in order to turn linear polymers from soluble to completely insoluble, it is enough to form 1-2 cross-links per macromolecule.

The most important characteristics of polymers are chemical composition, molecular weight and molecular weight distribution, degree of branching and flexibility of macromolecules, stereoregularity, etc. Properties of polymers. strongly dependent on these characteristics.

Preparation of polymers

Natural polymers are formed during biosynthesis in the cells of living organisms. Using extraction, fractional precipitation, and other methods, they can be isolated from plant and animal raw materials. Synthetic polymers are obtained by polymerization and polycondensation. Carbochain polymers are usually synthesized by polymerization of monomers with one or more multiple carbon-carbon bonds or monomers containing unstable carbocyclic groups (for example, from cyclopropane and its derivatives). Heterochain polymers are obtained by polycondensation, as well as polymerization of monomers containing multiple carbon-element bonds (for example, C \u003d O, C º N, N \u003d C \u003d O) or weak heterocyclic groups (for example, in olefin oxides, lactams).

Application of polymers

Due to mechanical strength, elasticity, electrical insulation and other valuable properties, polymer products are used in various industries and in everyday life. The main types of polymeric materials are plastics, rubber, fibers (see Textile fibers, Chemical fibers), varnishes, paints, adhesives, and ion-exchange resins. The importance of biopolymers is determined by the fact that they form the basis of all living organisms and are involved in almost all life processes.

History reference. The term "polymeria" was introduced into science by I. Berzelius in 1833 to denote a special type of isomerism, in which substances (polymers) having the same composition have different molecular weights, for example, ethylene and butylene, oxygen and ozone. Thus, the content of the term did not correspond to modern ideas about polymers. "True" synthetic polymers were not yet known at that time.

A number of polymers were apparently obtained as early as the first half of the 19th century. However, chemists then usually tried to suppress polymerization and polycondensation, which led to the "gum" of the products of the main chemical reaction, i.e., in fact, to the formation of a polymer. (Until now, polymers were often referred to as "resins"). The first references to synthetic polymers date back to 1838 (polyvinylidene chloride) and 1839 (polystyrene).

The chemistry of polymers arose only in connection with the creation by A. M. Butlerov of the theory of chemical structure (early 60s of the 19th century). A. M. Butlerov studied the relationship between the structure and relative stability of molecules, which manifests itself in polymerization reactions. The science of polymers received its further development (until the end of the 1920's) mainly due to the intensive search for methods for the synthesis of rubber, in which the leading scientists of many countries participated (G. Bouchard, W. Tilden, German scientist C. Garries , I. L. Kondakov, S. V. Lebedev and others). In the 30s. the existence of free radical (H. Staudinger and others) and ionic (American scientist F. Whitmore and others) mechanisms of polymerization was proved. The work of W. Carothers played an important role in the development of ideas about polycondensation.

From the beginning of the 20s. 20th century theoretical ideas about the structure of polymers are also being developed. Initially, it was assumed that such biopolymers as cellulose, starch, rubber, proteins, as well as some synthetic polymers similar in properties to them (for example, polyisoprene), consist of small molecules with an unusual ability to associate in solution into colloidal complexes due to non-covalent connections (the theory of "small blocks"). The author of a fundamentally new idea of ​​polymers as substances consisting of macromolecules, particles of unusually large molecular weight, was G. Staudinger. The victory of the ideas of this scientist (by the beginning of the 1940s) forced us to consider polymers as a qualitatively new object of study in chemistry and physics.

Literature .: Encyclopedia of polymers, vol. 1-2, M., 1972-74; Strepikheev A. A., Derevitskaya V. A., Slonimsky G. L., Fundamentals of chemistry of macromolecular compounds, 2nd ed., [M., 1967]; Losev I. P., Trostyanskaya E. B., Chemistry of synthetic polymers, 2nd ed., M., 1964; Korshak V. V., General Methods synthesis of macromolecular compounds, M., 1953; Kargin V. A., Slonimsky G. L., Brief essays in Physics and Chemistry of Polymers, 2nd ed., M., 1967; Oudian J., Fundamentals of polymer chemistry, trans. from English, M., 1974; Tager A. A., Physical Chemistry of Polymers, 2nd ed., M., 1968; Tenford Ch., Physical chemistry of polymers, trans. from English, M., 1965.

V. A. Kabanov. Source www.rubricon.ru

Polymers are compounds of the macromolecular type. Their basis is monomers, from which the macrochain of polymeric substances is formed. The use of polymers makes it possible to create materials with high level strength, wear resistance and a number of other useful characteristics.

Classification of polymers

Natural. Formed naturally. Example: amber, silk, natural rubber.

Synthetic. Produced in the laboratory and do not contain natural ingredients. Example: polyvinyl chloride, polypropylene, polyurethane.

artificial. Produced in the laboratory, but they are based on natural ingredients. Example: celluloid, nitrocellulose.

The types of polymers and their applications are very diverse. Most of the objects that surround a person are created using these materials. Depending on the type, they have different properties, which determine the scope of their application.

There are a number of common polymers that we encounter on a daily basis without even noticing:

• Polyethylene. It is used for the production of packaging, pipes, insulation and other products where moisture resistance, resistance to aggressive environments and dielectric characteristics are required.
• Phenol formaldehyde. It is the basis of plastics, varnishes and adhesives.
• Synthetic rubber. It has better strength characteristics and abrasion resistance than natural. Rubber and various materials based on it are made from it.
• Polymethyl methacrylate is a well-known plexiglass. Used in electrical engineering, as well as a structural material in other industrial areas.
• Polyamyl. It is used to make fabric and thread. These are kapron, nylon and other synthetic materials.
• Polytetrafluoroethylene, aka Teflon. Used in medicine Food Industry and various other areas. Everyone knows Teflon-coated pans, which were once very popular.
• Polyvinyl chloride, aka PVC. Often found in the form of a film, used for the manufacture of cable insulation, leather substitutes, window profiles, stretch ceilings. It has a very wide range of uses.
• Polystyrene. It is used for the production of household products and a wide range of building materials.
• Polypropylene. Pipes, containers, non-woven materials, household products, building adhesives and mastics are made from this polymer.

Where are polymers used?

The scope of polymeric materials is very wide. Now we can say with confidence - they are used in industry and production in almost any field. Due to their properties, polymers have completely replaced natural materials, which are significantly inferior to them in terms of characteristics. Therefore, it is worth considering the properties of polymers and their applications.

By classification, materials can be divided into:

• composites;
• plastics;
• films;
• fibers;
• varnishes;
• rubber;
• adhesive substances.

The quality of each variety determines the scope of polymers.

Life

Looking around, we can see a huge number of products made of synthetic materials. These are the details household appliances, fabrics, toys, kitchen utensils and even household chemicals. In fact, this is a huge range of products from an ordinary plastic comb to washing powder.

This widespread use is due to the low cost of production and high quality characteristics. Products are durable, hygienic, do not contain components harmful to the human body and are universal. Even ordinary nylon tights are made of polymer components. Therefore, polymers in everyday life are used much more often than natural materials. They are significantly superior to them in terms of quality and provide low price products.

Examples:

• plastic utensils and packaging;
• parts of various household appliances;
• synthetic fabrics;
• toys;
• kitchen utensils;
• bathroom products.

Any thing made of plastic or with the inclusion of synthetic fibers is made on the basis of polymers, so the list of examples can be endless.

Building sector

The use of polymers in construction is also very extensive. They began to be used relatively recently, about 50-60 years ago. Now most of building materials are produced using polymers.

Main directions:

• production of fencing and building structures various types;
• adhesives and foams;
• production engineering communications;
• materials for heat and waterproofing;
• Self-leveling floors;
• various finishing materials.

In the field of enclosing and building structures, these are polymer concrete, composite reinforcement and beams, frames for double-glazed windows, polycarbonate, fiberglass and various other materials of this type. All polymer-based products have high strength characteristics, long term services and resistance to negative natural phenomena.

Adhesives are resistant to moisture and excellent adhesion. They are used for bonding various materials and have high bonding strength. Foam - perfect solution for sealing joints. They provide high heat-saving characteristics and have a huge number of varieties with different qualities.

The use of polymeric materials in the production of engineering communications is one of the most extensive areas. They are used in water supply, power supply, heat saving, equipment of sewer networks, ventilation and heating systems.

Materials for thermal insulation have excellent heat-saving characteristics, low weight and affordable cost. Waterproofing has a high level of water resistance and can be produced in various forms(roll products, powder or liquid mixtures).

Polymer floors are a specialized material that allows you to create a perfectly flat surface on a rough basis without laborious work. This technology is used in both domestic and industrial construction.

Modern industry produces a wide range finishing materials based on polymers. They can have a different structure and form of release, but in terms of characteristics they always surpass natural finish and have a much lower cost.

The medicine

The use of polymers in medicine is widespread. The simplest example is disposable syringes. At the moment, about 3 thousand products used in the medical field are produced.

Silicones are the most commonly used in this area. They are indispensable when carrying out plastic surgery, creating protection on burn surfaces, as well as manufacturing various products. In medicine, polymers have been used since 1788, but in limited quantities. And in 1895, they become more widespread after an operation in which the bone defect was closed with a celluloid-based polymer.

All materials of this type can be divided into three groups according to the application:

• Group 1 - for introduction into the body. These are artificial organs, prostheses, blood substitutes, glues, drugs.
• Group 2 - polymers that have contact with tissues, as well as substances intended for introduction into the body. These are containers for storing blood and plasma, dental materials, syringes and surgical instruments, components of medical equipment.
• Group 3 - materials that do not have contact with tissues and are not introduced into the body. These are equipment and instruments, laboratory glassware, inventory, hospital supplies, bedding, spectacle frames and lenses.

Agriculture

Polymers are most actively used in greenhouses and land reclamation. In the first case, there is a need for various films, agrofibre, cellular polycarbonate, as well as fittings. All this is necessary for the construction of greenhouses.

In melioration, pipes made of polymeric materials are used. They have less weight than metal ones, affordable cost and longer service life.

food industry

In the food industry, polymeric materials are used for the manufacture of containers and packaging. May be in the form of hard plastics or films. The main requirement is full compliance with sanitary and epidemiological standards. One cannot do without polymers in food engineering. Their use allows you to create surfaces with minimal adhesion, which is important when transporting grain and other bulk products. Also, anti-adhesion coatings are needed in the lines of baking bread and the production of semi-finished products.

Polymers are used in various fields of human activity, which leads to their high demand. It is impossible to do without them. Natural materials cannot provide a number of characteristics necessary to meet specific conditions of use.