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Polymer materials: technology, types, production and application. Types of polymer materials

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Introduction

1. Polymer composition

2. Classification of polymers

3. Structure of polymers

4. Properties of polymers

5. Application of polymers

Introduction

Polymers are high-molecular substances, without which today it is difficult to imagine science and technology, convenience and comfort, the molecules of which consist of repeating structural elements - links connected in chains by chemical bonds, in quantities sufficient to produce specific properties. Specific properties include the following abilities: the ability to undergo significant mechanical reversible highly elastic deformations; to the formation of anisotropic structures; to the formation of highly viscous solutions when interacting with a solvent; To sudden change properties when adding insignificant additives of low molecular weight substances. Such materials serve as a worthy replacement for metals.

1. Polymer composition

Polymers are substances whose macromolecules consist of numerous repeating elementary units that represent the same group of atoms. The molecular weight of molecules ranges from 500 to 1,000,000. In polymer molecules, there is a main chain, which is built from a large number of atoms. The side chains are shorter.

Polymers whose main chain contains identical atoms are called homochain, and if there are carbon atoms, they are called carbochain. Polymers whose main chain contains different atoms are called heterochain.

Macromolecules of polymers are divided by shape into linear, branched, flat, ribbon, spatial, as shown in Figure 1.

Polymer molecules are obtained from initial low-molecular-weight products - monomers - by polymerization and polycondensation. Polycondensation polymers include phenol-formaldehyde resins, polyesters, polyurethanes, and epoxy resins. High-molecular compounds of the polymerization type include polyvinyl chloride, polyethylene, polystyrene, and polypropylene. High-polymer and high-molecular compounds are the basis of organic nature - animal and plant cells consisting of protein.

Figure 1 - Structures of polymer molecules:

a) linear, b) branched, c) ribbon, d) flat, e) spatial

2. Classification of polymers

Based on their origin, polymers are divided into natural (biopolymers), for example proteins, nucleic acids, natural resins, and synthetic, for example polyethylene, polypropylene, phenol-formaldehyde resins. Atoms or atomic groups can be located in a macromolecule in the form of: an open chain or an elongated sequence of cycles (linear polymers, for example natural rubber); branched chains (branched polymers, such as amylopectin), three-dimensional networks (cross-linked polymers, such as cured epoxy resins). Polymers whose molecules consist of identical monomer units are called homopolymers.

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

Polymers whose macromolecules contain several types of monomer units are called copolymers. Copolymers in which units of each type form sufficiently long continuous sequences that replace each other within the macromolecule are called block copolymers. To the internal links of the macromolecule of one chemical structure circuits of a different structure can be connected. Such copolymers are called graft copolymers.

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

Depending on the composition of the main (main) chain, polymers are divided into: heterochain, the main chain of which contains atoms of various elements, most often carbon, nitrogen, silicon, phosphorus, and homochain, the main chain of which is 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 are polyesters (polyethylene terephthalate, polycarbonates), polyamides, urea-formaldehyde resins, proteins, and some organosilicon polymers. Polymers whose macromolecules, along with hydrocarbon groups, contain atoms of inorganogenic elements are called organoelement. A separate group of polymers is formed by inorganic polymers, for example plastic sulfur and polyphosphonitrile chloride.

3. Structure of polymers

Elastomers

Elastomers are synthetic materials with elastic properties. They change their shape without difficulty; if the tension is relieved, they return to their original shape. Elastomers differ from other elastic synthetic materials in that their elasticity is more dependent on temperature.

Elastomers consist of spatially networked macromolecules. The molecular network of elastomers has wide cells. When changing shape, the cells move apart without destroying the connection points. After the stress is removed, the cells, like rubber, are attracted to their original position, and the synthetic material again takes its original shape.

Rubber is a product of vulcanization of rubber. Technical rubber is a composite material that can contain up to 15-20 ingredients that perform various functions. The main difference between rubber and other polymeric materials is the ability to undergo large, reversible, highly elastic deformations over a wide temperature range, including room temperature and above. low temperatures. The irreversible, or plastic, component of rubber deformation is much less than that of rubber, since rubber macromolecules are connected in rubber by transverse chemical bonds (vulcanization network). Rubber (a product of rubber vulcanization) is superior to rubber in strength properties, heat and frost resistance, resistance to aggressive environments, etc.

Plastics

Plastics are organic materials based on polymers that can soften when heated and take on a certain stable shape under pressure. Simple plastics consist of only chemical polymers. Complex plastics include additives: fillers, plasticizers, dyes, hardeners, catalysts. Plastics are produced monolithic - in the form of thermoplastic and thermosetting, gas-filled - with a cellular structure.

Thermoplastic plastics include polyethylene low pressure, polypropylene, impact-resistant polystyrene, polyvinyl chloride, fiberglass, polyamides, etc.

Thermosetting plastics include: rigid polyurethane foams, aminoplastics, etc.

Gas-filled plastics include polyurethane foams, a gas-filled ultra-lightweight structural material.

polymer chemical property

4. Properties of polymers

Linear polymers have a specific set of physicochemical and mechanical properties. The most important of these properties: the ability to form high-strength anisotropic highly oriented fibers and films, the ability to undergo large, long-term reversible deformations; the ability to swell in a highly elastic state before dissolving; high viscosity of solutions. This set of properties is due to the high molecular weight, chain structure, and flexibility of macromolecules. When moving from linear chains to branched, sparse three-dimensional networks and, finally, to dense mesh structures, this set of properties becomes less and less pronounced. Highly cross-linked polymers are insoluble, infusible and incapable of highly elastic deformations.

Properties of plastics

Plastics are characterized by low density, extremely low electrical and thermal conductivity, and not very high mechanical strength. When heated they decompose. Insensitive to humidity, resistant to strong acids and bases. Physiologically almost harmless.

The properties of plastics can be modified by copolymerization or stereospecific polymerization methods, by combining different plastics with each other or with other materials, such as glass fiber, textile fabric, introducing fillers and dyes, plasticizers, as well as varying raw materials, for example the use of appropriate ones.

To impart special properties to plastic, plasticizers (silicon, etc.), flame retardants, and antioxidants (unsaturated hydrocarbons) are added to it.

Properties of rubbers

An important property of rubber is elasticity, the ability to undergo large reversible deformations over a wide temperature range. At the molecular level, this is explained by the fact that during deformation, the chains of molecules stretch and slide relative to each other; after the load is removed, the molecular chains, under the influence of thermal motion, return to their previous position, corresponding to the original one, but they still shift slightly. This change in the positions of the molecular chains characterizes permanent deformation. Rubber has high elasticity and high deformability. Rubber has a low hardness, which is determined by the content of fillers and plasticizers in it, as well as the degree of vulcanization. Rubbers resist wear well and insulate heat and sound well. They are good diamagnetic and dielectric materials. There are rubbers with oil, gasoline, water, steam, heat resistance, as well as resistance to aggressive environments and fatigue (reduced mechanical properties).

5. Application of polymers

Polymers are used in all spheres of human life:

Active use of polymers in agriculture allows you not to lose the harvest due to the weather, but increase it by about 30%. For example, greenhouses.

In sports where it is traditional to play on grass (football, tennis, croquet), polymers are indispensable; artificial grass is produced from them.

However, the main consumer of almost all materials produced in our country, including polymers, is industry. The use of polymer materials in mechanical engineering is growing at a rate that has no precedent in all of human history. For example, in 1976 1. the mechanical engineering of our country consumed 800,000 tons of plastics, and in 1960 - only 116,000 tons. It is interesting to note that ten years ago 37-38% of all products produced in our country were sent to mechanical engineering plastics, and in 1980 the share of mechanical engineering in the use of plastics decreased to 28%. And the point here is not that the need might decrease, but that other sectors of the national economy began to use polymer materials in agriculture, construction, and the light and food industries even more intensively.

List of used literature

1. Materials science: Textbook for universities / B.N. Arzamasov, V.I. Makarova, G.G. Mukhin and others; Under general Ed. B.N. Arzamasova, G.G. Mukhina. - 7th ed., stereotype. - M.: Publishing house of MSTU im. N.E. Bauman, 2005. - 648 pp.: ill.

2. Gorchakov G.I., Bazhenov Yu.M. Construction materials/ G.I. Poller V.I. "Chemistry on the way to the third millennium." - 1979. Ratinov A.M., Ivanov D.P. “Chemistry in construction.” Directory.

3. Soviet Vasyutin D.O. "Polymers".

4. Encyclopedic dictionary.

5. http://www.e-reading-lib.org/chapter.php/99301/51/Buslaeva_-_Materialovedenie._Shpargalka.html

6. http://museion.ru/1.5/rezina.html

7. Free Encyclopedia Wikipedia.

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General characteristics of polymers

Polymers are high-molecular substances whose molecules consist of repeating structural units linked to each other by chemical bonds. Polymers can be organic or inorganic, amorphous or crystalline substances. Polymers always contain a large number of monomer units; if this amount is too small, then it is no longer a polymer, but an oligomer. The number of units is considered sufficient if the properties do not change when adding a new monomer unit.

Rice. 1. Polymer structure.

The substances from which polymers are made are called monomers.

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

The polymerization reaction is characteristic of many organic substances that contain double or triple bonds.

For example: polyethylene formation reaction:

nCH 2 =CH 2 —> [-CH 2 -CH 2 -]n

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

Polyethylene is produced at high temperatures and high blood 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 repeated many times in a macromolecule.

Types of polymers

Based on their origin, polymers can be divided into three types:

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

Rice. 3. Rubber.

synthetic. Synthetic polymers are obtained in laboratory conditions and are synthesized by humans. 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 in laboratory conditions, but on the basis of natural polymers. Artificial polymers include celluloid, cellulose acetate, and nitrocellulose.

From the point of view of 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, and polygermanes. Organoelement polymers include a mixture of both organic and inorganic polymers. The main chain is always inorganic, the side chains are organic. Examples of polymers include polysiloxanes, polycarboxylates, and polyorganocyclophosphazenes.

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

A polymer is a complex compound that has a high molecular weight and consists of a number of constituent units that are connected to each other through chemical bonds. Most often, the structure of a polymer is based on a monomer - a structural fragment consisting of several atoms.

Most polymers are produced synthetically (although there are also natural polymers) - using polymerization and polycondensation reactions. So, for example, ethylene turns into polyethylene, propylene into polypropylene, etc.

Properties of polymers

The properties of polymers are largely determined by their composition, but some features are common to most polymers. As a matter of fact, it is these features that provide their widest practical purpose. Polymers are elastic, flexible and not brittle. The macromolecules that make up the polymer can change their orientation under the influence of a certain mechanical field; this feature is used in the production of films.

Another interesting property of polymers is the ability to abruptly change their physical and mechanical properties when exposed to a small amount of a reagent. This feature is used in rubber vulcanization, leather tanning, etc.

Types of polymers

Polymers are classified according to a number of characteristics. The most significant classifications are by origin and chemical composition.

There are polymers by origin:

Natural - existing in nature (starch, proteins, etc.);
Synthetic - obtained synthetically (polyethylene, polypropylene, etc.);
Artificial - obtained synthetically from natural polymers (nitrocellulose, methylcellulose, etc.).

Polymers are classified according to their chemical composition:

Organic;
Inorganic;
Organoelement - contain both organic and inorganic structures.

Polymers in practice

Polymers are found wide application in a variety of fields - mechanical engineering, textile industry, medicine, agriculture. There is also a place for polymer compounds in everyday life. Things that contain polymers surround us everywhere - various types of fabrics (wool, silk, leather, etc.), plastic products, binding building mixtures (cement, clay, etc.), rubber products, dishes... In In general, the role of polymer compounds in our lives is truly enormous. Now you know what a polymer is.

Preface

All types of polymeric materials are substances in which each molecule is a chain of tens or hundreds of thousands of identical groups of atoms connected in series, and the same group of atoms is rhythmically repeated many times.

Contents

The main polymeric materials include resins and plastics. Depending on whether it is a thermoplastic polymer or a thermoset, the material can either soften and harden many times, or, with a single heating, turn into a solid state and permanently lose its ability to melt. The most commonly used modern polymer materials are dispersions, latexes and adhesives.

What are building polymer materials

What are polymer materials and how are they used in construction? All types of polymeric materials are substances in which each molecule is a chain of tens or hundreds of thousands of identical groups of atoms connected in series, and the same group of atoms is rhythmically repeated many times.

The main types of polymer materials are divided into thermoplastic and thermosetting. Thermoplastic polymers are capable of repeatedly softening and hardening with changes in temperature, and also easily swell and dissolve in organic solvents. These include polystyrene, polyethylene and polyvinyl chloride (polyvinyl chloride) resins and plastics.

The main property of thermosetting polymer materials is the transition when heated to an insoluble solid state and the irreversible loss of the ability to melt. Such polymers include phenol-formaldehyde and urea-formaldehyde, polyester and epoxy resins.

Certain types of polymer materials in construction, under the influence of heat, light and atmospheric oxygen, change their properties over time: they lose flexibility, elasticity, in other words, they age.

To prevent aging of modern polymer building materials, special stabilizers (anti-aging agents) are used, which are various organometallic compounds of lead, barium, cadmium, etc. For example, Tinuvin P is used as a stabilizer.

What polymer materials are there and what their main characteristics are, you will learn on this page.

Polymer plastic materials and their properties

One of the main types of polymeric materials is plastics. They are a group organic materials, which are based on synthetic or natural resin-like high-molecular substances that can be molded under heat and pressure, stably maintaining their given shape.

Polymer plastic materials have good thermal insulation and electrical insulation qualities, corrosion resistance and durability. The average density of plastics is 15-2200 kg/m3; compressive strength - 120-160 MPa. Plastics are endowed with good electrical and thermal insulation properties, corrosion resistance and durability. Some of them are transparent and have high adhesive properties, and also tend to form thin films and protective coatings. Due to their properties, these polymeric materials are widely used in construction, mainly in combination with binders, metals and stone materials.

Plastics consist of a binder - a polymer, a filler, a plasticizer and a curing accelerator. Mineral dyes are also used in the production of colored plastics.

Organic and mineral powders, asbestos, wood and glass fibers, paper, glass and cotton fabrics, wood veneer, asbestos cardboard, etc. are used as fillers in the manufacture of this type of polymer materials. Fillers not only reduce the cost of the material, but also improve certain properties of plastics : Increases hardness, strength, acid resistance and heat resistance. They must be chemically inert, low volatile and non-toxic. Plasticizers in the manufacture of plastics are zinc acid, aluminum stearate and others, which give the material greater plasticity. Catalysts (accelerators) are used in plastics to speed up curing. An example of a catalyst is lime or methenamine, which are used to cure phenol-formaldehyde polymer.

Synthetic polymer materials and their applications

According to the production method, synthetic polymer materials are divided into two classes: class A - polymers obtained by chain polymerization; class B - polymers obtained by polycondensation and stepwise polymerization.

The polymerization process is a combination of identical and different molecules. No by-products are formed during polymerization.

The polycondensation process is a combination large quantity identical and different polyreactive molecules of low molecular weight substances, resulting in the formation of a high molecular weight substance. During the polycondensation process, water, hydrogen chloride, ammonia and other substances are released.

Silicone resins- This special group high molecular weight compounds. The peculiarity of these polymer building materials is that they have the properties of both organic and inorganic substances.

The physical and mechanical characteristics of these polymeric materials are virtually unaffected by temperature fluctuations compared to conventional resins, and they are also highly hydrophobic and heat resistant. Organosilicon resins are used to obtain various products resistant to action elevated temperatures(400-500°C).

The main area of application of these synthetic polymeric materials is the production of concrete and mortars to increase their durability. They are also used in the form of protective coatings on natural and artificial stone materials (concrete, limestone, travertine, marble, etc.). Impregnation has protective effect for 6-10 years, after which it should be renewed.

For impregnation surfaces of products made of natural stone and others building structures water-repellent organosilicon liquids (OSH) are used, which are dissolved with organic solvents before use, as well as an aqueous 50% emulsion (milk- white), which is mixed with water in a ratio of 1:10 before use.

Polyvinyl acetate dispersion (PVA) is a product of the polymerization of vinyl acetate into aquatic environment in the presence of an initiator and a protective colloid. It is a viscous, white, homogeneous liquid, without screams or foreign inclusions.

Depending on the viscosity, PVA is produced in three grades: N - low-viscosity, C - medium-viscosity, B - high-viscosity. It is used in the production of polymer-cement mortars, mastics, and pastes, which are used in facing work.

Synthetic latex SKS-65GP- a product of co-polymerization of butadiene with styrene in a ratio of 35:65 (by weight) in an aqueous emulsion using nekal and sodium soap of synthetic fatty acids as an emulsifier. Latex SKS-65GP is used in the production of polymer concrete, emulsion paints, mastics and pastes used in facing work. Latex is also used in various coatings.

Physico-chemical properties of this polymer building material latex SKS-65GP:

dry matter content,%, not less than 47;
content of unpolymerized styrene, %, not more than 0.08;
hydrogen ion concentration (pH), not less than 11;
surface tension, dynes/cm2, no more than 40;
viscosity, s - 11-15;
Ash content,%, no more than 1.5.

Synthetic latex SKS-ZOSHR is a product of joint polymerization of butadiene with styrene in an aqueous emulsion, used as a binder or adhesive material for facing work.

Physico-chemical properties of SKS-ZOSHR latex:

dry matter content,%, not less than 33;
gelatinization temperature, °C, not higher than 14;
free alkali content, %, not more than 0.15.

Characteristics of polymer adhesive materials

Polymer adhesive materials are produced in the form of liquids, powders and films.

There are two types of liquid adhesives. The first type of adhesive compositions are rubbers, resins or cellulose derivatives dissolved in an organic volatile solvent (alcohol or acetone). After the solvent evaporates, a solid adhesive joint is formed. The second type of adhesive composition is aqueous solutions resins specially prepared for adhesives. Such solutions at proper storage do not thicken for several months. Liquid adhesives contain 40-70% solid adhesive.

The most common liquid adhesives are melamine-formaldehyde, phenol-formaldehyde, urea-formaldehyde, rubber, epoxy, polyvinyl acetate, as well as adhesives with the addition of silicones.

CMC glue (sodium salt of carboxymethylcellulose) is used in the manufacture of mastics and solutions used in.

Carbinol glue (vinylacetylene carbolene) is a viscous transparent liquid of light orange color with high adhesive ability. That's why it is called universal. He is capable of gluing various materials, even such as concrete, stone, metal, wood. Hardened carbinol glue is resistant to oils, acids, alkalis, gasoline, acetone and water.

Concentrated nitric acid or benzoyl peroxide are used as catalysts to accelerate the hardening of carbinol glue. The latter is an explosive powder, so it should be stored away from fire.

Carbinol glue is produced on the basis of carbinol syrup (100 parts by weight) in two compositions: in the 1st one, benzoyl peroxide (1-3 parts by weight) is added as a hardener, in the 2nd - concentrated nitric acid (1-2 parts by weight). h.).

Carbinol glue is stored at a temperature of 20°C and in the dark, since under the influence of light it loses its adhesive ability.

Epoxy adhesive is a transparent viscous liquid of light brown color with high adhesive ability. It is used for gluing stone, concrete, ceramic tiles. The hardened seam of epoxy adhesive is resistant to acids, alkalis, solvents, water, as well as to high mechanical loads. The hardeners for epoxy resin are polyethylene polyamine or hexamethylenediamine, and the plasticizer is dibutyl phtholate.

If the connection between macromolecules is carried out using weak van der Waals forces, they are called thermoplastics, if through chemical bonds - thermosets. Linear polymers include, for example, cellulose, branched polymers, for example, amylopectin, and there are polymers with complex spatial three-dimensional structures.

In the structure of a polymer, a monomer unit can be distinguished - a repeating structural fragment that includes several atoms. Polymers consist of a large number of repeating groups (units) of the same structure, for example, polyvinyl chloride (-CH 2 -CHCl-) n, natural rubber, etc. High molecular weight compounds, the molecules of which contain several types of repeating groups, are called copolymers or heteropolymers.

A polymer is formed from monomers as a result of polymerization or polycondensation reactions. Polymers include numerous natural compounds: proteins, nucleic acids, polysaccharides, rubber and other organic substances. In most cases, the concept refers to organic compounds however, there are also many inorganic polymers. A large number of polymers are obtained synthetically based on the simplest compounds of elements natural origin through polymerization reactions, polycondensation and chemical transformations. The names of polymers are formed from the name of the monomer with the prefix poly-: poly ethylene, poly propylene, poly vinyl acetate, etc.

Peculiarities

Special mechanical properties

elasticity - the ability to undergo high reversible deformations under a relatively small load (rubbers);
low fragility of glassy and crystalline polymers (plastics, organic glass);
the ability of macromolecules to orient under the influence of a directed mechanical field (used in the manufacture of fibers and films).

Features of polymer solutions:

high solution viscosity at low polymer concentration;
The dissolution of the polymer occurs through the swelling stage.

Special chemical properties:

the ability to dramatically change its physical and mechanical properties under the influence of small quantities of a reagent (vulcanization of rubber, tanning of leather, etc.).

The special properties of polymers are explained not only by their large molecular weight, but also by the fact that macromolecules have a chain structure and are flexible.

Copolymers

Polymers made from different monomers or chemically bonded molecules of different polymers are called copolymers. For example, impact-resistant polystyrene is a polystyrene-polybutadiene copolymer.

Copolymers differ in structure, manufacturing technology and resulting properties. Technologies created for 2014:

random copolymers, formed by chains containing chemical groups of different nature, are obtained by polymerization of a mixture of several starting monomers;
alternating copolymers are characterized by chains in which radicals of different monomers alternate;
graft copolymers are formed by attaching chains of molecules of a second monomer to the side of macromolecules formed from the main monomer;
comb copolymers are graft copolymers with very long side chains;
block copolymers are built from fairly long chains (blocks) of one monomer, connected at the ends to fairly long chains of another monomer.

Properties of copolymers

Comb-shaped copolymers can be composed of materials with different properties, which gives such a copolymer fundamentally new properties, for example, liquid crystalline.

In block copolymers composed of components with different properties, superlattices arise, built from blocks of different chemical natures separated into a separate phase. The sizes of the blocks depend on the ratio of the initial monomers. Thus, tensile strength of up to 40% is added to brittle polystyrene by copolymerization with 5-10% polybutadiene, and impact-resistant polystyrene is obtained, and with 19% polystyrene in polybutadiene the material exhibits rubber-like behavior.

Classification

According to their chemical composition, all polymers are divided into organic, organoelement, inorganic.

Organic polymers.
Organoelement polymers. They contain inorganic atoms (Si, Ti, Al) in the main chain of organic radicals, which combine with organic radicals. They don't exist in nature. An artificially obtained representative is organosilicon compounds.
Inorganic polymers. They do not contain in a repeating unit C-C connections, but are capable of containing organic radicals as side substituents.

It should be noted that in engineering, polymers are often used as components of composite materials, for example, fiberglass. Composite materials are possible, all components of which are polymers (with different compositions and properties).

Based on the shape of macromolecules, polymers are divided into linear, branched (a special case is star-shaped), ribbon, flat, comb-shaped, polymer networks, and so on.

Polymers are classified according to polarity (affecting solubility in various liquids). The polarity of polymer units is determined by the presence in their composition of dipoles - molecules with an isolated distribution of positive and negative charges. In nonpolar units, the dipole moments of atomic bonds are mutually compensated. Polymers whose units have significant polarity are called hydrophilic or polar. Polymers with non-polar units - non-polar, hydrophobic. Polymers containing both polar and non-polar units are called amphiphilic. Homopolymers, each unit of which contains both polar and nonpolar large groups, are proposed to be called amphiphilic homopolymers.

In relation to heating, polymers are divided into thermoplastic And thermosetting. Thermoplastic polymers (polyethylene, polypropylene, polystyrene) soften when heated, even melt, and harden when cooled. This process is reversible. Thermoset When heated, polymers undergo irreversible chemical destruction without melting. Molecules of thermosetting polymers have a nonlinear structure obtained by cross-linking (for example, vulcanization) of chain polymer molecules. The elastic properties of thermosetting polymers are higher than those of thermoplastics; however, thermosetting polymers have practically no fluidity, as a result of which they have a lower fracture stress.

Natural organic polymers are formed in plant and animal organisms. The most important of them are polysaccharides, proteins and nucleic acids, of which the bodies of plants and animals largely consist and which ensure the very functioning of life on Earth. It is believed that the decisive stage in the emergence of life on Earth was the formation of more complex, high-molecular molecules from simple organic molecules (see Chemical evolution).

Types

Synthetic polymers. Artificial polymer materials

Man has been using natural polymer materials in his life for a long time. These are leather, fur, wool, silk, cotton, etc., used for the manufacture of clothing, various binders (cement, lime, clay), which, with appropriate processing, form three-dimensional polymer bodies, widely used as building materials. However, the industrial production of chain polymers began at the beginning of the 20th century, although the prerequisites for this appeared earlier.

Almost immediately, the industrial production of polymers developed in two directions - by processing natural organic polymers into artificial polymer materials and by producing synthetic polymers from organic low-molecular compounds.

In the first case, large-scale production is based on cellulose. The first polymer material from physically modified cellulose - celluloid - was obtained in the middle of the 19th century. Large-scale production of cellulose ethers and esters was established before and after World War II and continues to this day. Films, fibers, paints and varnishes and thickeners are produced on their basis. It should be noted that the development of cinema and photography was possible only thanks to the advent of transparent nitrocellulose film.

The production of synthetic polymers began in 1906, when Leo Baekeland patented the so-called bakelite resin - a condensation product of phenol and formaldehyde, which turns into a three-dimensional polymer when heated. For decades it has been used to make housings for electrical appliances, batteries, televisions, sockets, etc., and is now more often used as a binder and adhesive.

The list is completed by the so-called unique polymers synthesized in the 60-70s of the 20th century. These include aromatic polyamides, polyimides, polyesters, polyether ketones, etc.; An indispensable attribute of these polymers is the presence of aromatic rings and (or) aromatic condensed structures. They are characterized by a combination of outstanding strength and heat resistance.

Fireproof polymers

Many polymers, such as polyurethanes, polyesters and epoxy resins, are prone to flammability, which is often unacceptable when used. practical application. To prevent this, various additives are used or halogenated polymers are used. Halogenated unsaturated polymers are synthesized by condensing chlorinated or brominated monomers, such as hexachloacid (CHEMTPA), dibromoneopentylglycol or tetrabromophthalic acid. The main disadvantage of such polymers is that when burned they can release gases, corrosive, which can have a detrimental effect on nearby electronics.

The action of aluminum hydroxide is based on the fact that under high temperature exposure water is released, which prevents combustion. To achieve the effect you need to add large quantities aluminum hydroxide: by weight 4 parts to one part unsaturated polyester resins.

Ammonium pyrophosphate acts on a different principle: it causes charring, which, together with the glassy layer of pyrophosphates, insulates the plastic from oxygen, inhibiting the spread of fire.

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