Many polymers are manufactured common. About polymers

Polymeric materials (plastics, plastics) are usually solidized composite compositions that are connected in which polymers are served, oligomers. The widespread name is "plastics" (which is not entirely correct) they got for the fact that when processing in products are in the plastic (fluid) state. Therefore, scientifically based titles - "Polymer materials", "Composite materials based on polymers".

Polymers (from Greek. Poly - Many, Meres - Parts) - It is high molecular chemical compounds, whose molecules consist of a huge number of multiple repeated elementary links of the same structure. Such molecules are called macromolecules. Depending on the location of atoms and atomic groups (elementary units), they may have a linear (chain), branched, mesh and spatial (three-dimensional) structure, which determines their physicomechanical 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 with many other atoms.

The formopolymers (prepuids, prepolymers) are also distinguished, which are compounds containing functional groups and capable of participating in the growth reactions or crosslinking the polymer chain to form high molecular weight linear and mesh polymers. First of all, these are also liquid polyols products with an excess of polyisocyndage or other compounds in the production of products from polyurethanes.

By origin, the 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 in the process of biosynthesis in cells of living and vegetable organisms. However, in most cases artificial and synthetic polymers are used in most cases.

The main raw materials for the production of polymers are by-products of coal and oil industry, fertilizer production, natural gasCellulose and other substances. The process of formation of such macromolecules and as a whole polymer is caused by the impact on the starting material (monomer) of the flow of light rays, the electrical discharges of high frequency currents, heating, pressure, etc.

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

When the polycondensation reaction, there are regrouping of atoms of two or several monomers and the separation of side low molecular weight products from the sphere of the reaction (for example, water, alcohols or other low molecular weight substances). Polyamides, polyesters, epoxy, phenoloformaldehyde, silicone and other synthetic polymers, called still resins, are obtained by polycondensation.

Depending on the attitude towards heating and solvents, polymers, as well as materials based on them, are divided into thermoplastic and thermosetting.

Thermoplastic polymers (thermoplastics) when processing in products can repeatedly move from a solid aggregate state into visco-fluid (melt), and when cooled, relent again. They have, as a rule, not a high temperature of the transition to visco-fluid state, are well processed with injection molding, extrusion and pressing. Forming products of them is a process of physical, which consists in solidification of liquid or softened material when it is cooling and chemical changes does not occur. Most of the thermoplastics are also able to dissolve in the corresponding solvents. Thermoplastic polymers have a linear or slightly branched structure of macromolecules. These include individual varieties of polyethylene, polyvinyl chloride, fluoroplastics, polyurethanes, bitumens, etc.

The thermosetting (reactoplasts) includes polymers, processing into the products of which are accompanied by chemical reaction The formation of a mesh or three-dimensional polymer (curing, stitching chains) and the transition from a liquid state into solid, occurs irreversible. The cured state is thermostable, and they lose the ability to re-transition to visco-fluid state (for example, phenoloaldehyde, polyester, epoxy polymers, etc.).

Classification and properties of polymeric materials

Polymer materials depending on the composition or number of components are divided into unauthorized, represented by only one binder (polymer) - organic glass, in most cases, polyethylene film; Filled, which may include fillets, plasticizers, stabilizers, hardeners, pigments - fiberglass, textolomate, linoleum and gas-filled (foam and poroplasts) - polystyrene foam, polyurethane foam, etc.

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

Hard - these are solid, elastic materials of amorphous structure having an elastic module of more than 1000 MPa. They are fragile destroyed with a slight lengthening at break. These include phenoplasts, aminoplasts, plastics based on glyphthalian and other polymers.

Density polymeric materials Most often is in the range of 900.1800 kg / m3, i.e. They are 2 times easier aluminum and is 5.6 times easier. At the same time, the density of porous polymeric materials (foam) can be 30..15 kg / m3, and dense to exceed 2,000 kg / m3.

The strength in compressing polymeric materials in most cases is superior to many traditional construction Materials (concrete, brick, wood) and is about 70 MPa, reinforced polymers, more than 200 MPa, with tension - for materials with powdered filler 100.150 MPa, in fiberglass - 276.414 MPa and more.

The thermal conductivity of such materials depends on their porosity and production technology. In foam and parental, it is 0.03.034 W / m-k, in the remaining - 0.2.0.7 W / MK or 500.600 times lower than that of metals.

The disadvantage of many polymeric materials is low heat resistance. For example, most of them (based on polystyrene, polyvinyl chloride, polyethylene and other polymers) heat resistance is 60.80 ° C. Based on phenolormaldehyde resins, heat resistance can reach 200 ° C and only on silicon polymers - 350 ° C.

Being hydrocarbon compounds, many polymeric materials are combustible or have low fire resistance. The flammable and burning with rich segments of soot include products based on polyethylene, polystyrene, cellulose derivatives. It is difficult to combine products based on polyvinyl chloride, polyester fiberglass, phenoplasts, which increased temperature Only charred. Non-combustible are polymeric materials with a large content of chlorine, fluorine or silicon.

Many polymeric materials for processing, burning and even heating distinguish dangerous substances such as carbon monoxide, phenol, formaldehyde, phosgene, hydrochloric acid, etc. Significant disadvantages are also a high thermal expansion coefficient - from 2 to 10 times higher than that of steel.

Polymeric materials are characterized by shrinkage during solidification, reaching 5.8%. In most part of them, a low modulus of elasticity is significantly lower than that of metals. With long loads, they have a large creep. With an increase in the temperature of the creep even more increases, which leads to undesirable deformations.

The term polymer is widely used in our time in the production of plastics and composite industry, quite often the word "polymer" is used to designate plastics. In fact, the term "polymer" means much more.

Specialists of the company NPP Simplex decided to tell in detail what polymers are:
The polymer is a substance with a chemical composition of molecules connected to long repeating chains. Due to this, all materials made of polymers have unique properties and can be adapted depending on their destination.
Polymers are both artificial and natural origin. The most common in nature is natural rubber, which is extremely useful and is used by humanity for several thousand years. Rubber (rubber) has excellent elasticity. This is the result of the fact that molecular chains in the molecule are extremely long. Absolutely all types of polymers have the properties of high elasticity, however, together with these properties, a wide range of additional additional spectrum useful properties. Depending on the purpose, the polymers can be finely synthesized for the most convenient and advantageous use of their specific properties.

The main physical properties of polymers:

• Impact resistance
• Rigidity
• Transparency
• Flexibility
• Elasticity

  Scientists chemists have long noticed one interesting featureassociated with polymers: if you look at the polymer chain under the microscope, then you can see that the visual structure and physical properties The chain molecules will mimic the real physical properties of the polymer.

  For example, if the polymer chain consists of tightly twisted between the threads of monomers and it is difficult to divide, then, most likely, this polymer will be strong and elastic. Or if the polymer chain on molecular level Shows elasticity, most likely, the polymer will have flexible properties.

  Polymer processing
  Most of the products from polymers can be changed and deformed under the influence of high temperatures, but the polymer itself may not change at the molecular level, and it will be possible to create a new product from it. For example, you can melt plastic containers and bottles and then make plastic containers or car parts from these polymers.

  Examples of polymers
  Below is a list of the most common polymers used in our time, as well as their main application:

  • Polypropylene (PP) - production of carpet, containers for products, flasks.
  • Neoprene - Hydrocyus
  • Poly-vinyl chloride) (PVC) - pipeline production, corrugated
  • Low density polyethylene (LDPE) - grocery packages
  • Polyethylene high density (HDPE) - Tara for detergents, bottles, toys
  • Polystyrene (PS) - Toys, Foam, Frameless Furniture
  • Polytetrafluoroethylene (PTFE, fluoroplast) - non-stick skumps, Electric isolation
  • Polymethyl methacrylate (PMMA, Plexiglas, Plexiglas) - Ophthalmology, production acrylic baths, Lighting technique
  • (PVA) - Paints, Adhesives

  

Polymers are macromolecular type compounds. Their base is the monomers from which the macro barreling of polymeric substances is formed. The use of polymers allows you to create materials possessing high levels Strength, wear resistance and a number of other useful characteristics.

Classification of polymers

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

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

Artificial. Produced in laboratory conditions, but they are based on natural components. Example: Celluloid, nitrocellulose.

Types of polymers and their use are very diverse. Most of the items that surround a person are created using these materials. Depending on the type, they have different properties that determine their scope.

There are a number of common polymers, with whom we face every day and do not even notice this:

• Polyethylene. It is used to produce packaging, pipes, insulation and other products, where it is required to ensure moisture resistance, resistance to aggressive media and dielectric characteristics.
• Phenol formaldehyde. It is the basis of plastics, varnishes and adhesive compositions.
• Synthetic rubber. It has the best strength characteristics and resistance to abrasion than natural. Rubber is made of it and various materials based on it.
• Polymethyl methacrylate - the well-known plexiglass. Used in electrical engineering, as well as structural material in other industrial areas.
• Polyamil. It makes fabric and threads from it. This is a kapron, nylon and other synthetic materials.
• Polytetrafluoroethylene, he is the Teflon. Used in medicine, food Industry and various other areas. Everyone knows a frying pan with teflon coating, which were sometimes very popular.
• Polyvinyl chloride, he is PVC. Often occurs in the form of a film, used to make insulation cables, leatherette, window profiles, stretch ceilings. It is very wide sphere use.
• Polystyrene. It is used for the production of household products and a wide range of building materials.
• Polypropylene. From this polymer are made pipes, containers, nonwovens, household products, construction adhesives and mastics.

Where polymers are used

The scope of polymer materials is very wide. Now you can say with confidence - they are used in industry and production in almost any field. Thanks to its qualities, the polymers were completely replaced natural materials, significantly inferior to them according to the 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 the use of polymers.

Life

Looking around, we can see great amount Products from synthetic materials. These are details household appliances, fabrics, toys, kitchenware and even household chemicals. In fact, it is a huge range of products from conventional plastic combing to washing powder.

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

Examples:

• plastic dishes and packaging;
• parts of various household appliances;
• synthetic fabrics;
• toys;
• kitchen accessories;
• products for bathrooms.

Any point of plastic or with the inclusion of synthetic fibers is made on the basis of polymers, so the list of examples may be infinite.

Building sector

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

Main directions:

• the manufacture of enclosing and building structures of various types;
• adhesive compositions and foam;
• production of engineering communications;
• materials for heat and waterproofing;
• self-leveling floors;
• various finishing materials.

In the field of enclosing and building structures, it is polymer concrete, composite fittings and beams, glass frames, polycarbonate, fiberglass and various other materials of this type. All products on polymeric basis Have high strength characteristics, long term Services and resistance to negative natural phenomena.

Adhesives are distinguished by resistance to moisture and excellent adhesion. They are used for gluing different materials and have high strength Connections. Foam is an ideal solution for sealing joints. They provide high heat-saving characteristics and have a huge amount of varieties with various qualities.

The use of polymeric materials in the field of engineering communications production is one of the most extensive directions. They are used in water supply, electrical supply, heat resistant, equipment sewage networks, ventilation and heating systems.

Materials for thermal insulation have excellent heat-saving characteristics, low weight and affordable cost. Waterproofing is distinguished by a high level of waterproof and can be produced in various form (Roll products, powder or liquid mixtures).

Polymer floors are a specialized material that allows you to create a perfectly smooth surface on a draft basis without labor-intensive work. This technology is used both in everyday life and in industrial construction.

Modern industry produces a wide range finishing materials Based on polymers. They can have various structure and the form of release, but according to the characteristics always exceed natural finish And have much less cost.

Medicine

The use of polymers in medicine is widespread. The easiest example is disposable syringes. On the this moment About 3 thousand products used in the medical sphere are produced.

Most often, silicones are used in this area. They are indispensable when performing plastic operations, creating protection on burn surfaces, as well as the manufacture of various products. In medicine, polymers were used since 1788, but in limited quantities. And 1895, they get wider distribution after the operation, during which the bone defect was closed with a polymer based on celluloid.

all materials this type It can be divided into three groups according to the application:

• 1 group - for introducing into the body. These are artificial organs, prostheses, blood substitutes, adhesives, drugs.
• 2 Group - polymers that have contact with tissues, as well as substances intended for introducing into the body. This is a container for blood storage and plasma, dental materials, syringes and surgical instrumentsMissing medical equipment.
• 3 Group - Materials that do not have contact with tissues and not introduced into the body. These are equipment and instruments, laboratory dishes, inventory, hospital supplies, bed linen, glasses for glasses and lenses.

Agriculture

The most active polymers are used in greenhouse and land reclamation. In the first case, there is a need for various films, agrovolok, cellular polycarbonate, as well as fittings. It is all necessary for the construction of greenhouses.

Pipes from polymeric materials are used in the amelioration. They have less weight than metal, affordable cost and longer service life.

Food industry

In the food industry, polymer materials are used for the manufacture of containers and packaging. May have a form of solid plastics or films. The main requirement is a complete compliance with sanitary and epidemiological standards. Do not do without polymers and 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 bread baking lines and semi-finished products.

Polymers are used in different industries Human activity, which causes their high demand. It is impossible to do without them. Natural materials A number of characteristics required for compliance with specific use conditions are not provided.

1. Based on polymers, fibers are obtained by improving solutions or melts through filters with subsequent solidification - these are polyamides, polyacrylonitriles, etc.

2. Polymer films are obtained by melting through fillers with sliding holes or applying to a moving tape. They are used as electrical insulating and packaging material, the basics of magnetic tapes.

3. Lucky - solutions of film-forming substances in organic solvents.

4. Adhesives, compositions capable of combining various materials due to the formation of strong links between their glue layer surfaces.

5. Plastics

6. Composites (composite materials) - polymer base reinforced by filler.

10.4.2. Observations of polymers

1. Polyethylene is resistant to an aggressive medium, moistureproof, is a dielectric. Pipes, electrical products, radio equipment parts, insulating films, cable shells of telephone and power lines are made of it.

2. Polypropylene - mechanically durable, racks to bend, abrasion, elastic. Apply for the manufacture of pipes, films, battery tanks, etc.

3. Polystyrene is resistant to acid action. It is mechanically durable, is a dielectric used as an electrical insulating and structural material in electrical engineering, radio engineering.

4. Polyvinyl chloride is difficult, mechanically durable, electrical insulating material.

5. Polytetrafluoroethylene (fluoroplast) - a dielectric does not dissolve in organic solvents. It has high dielectric properties in a wide range of temperatures (from -270 to 260ºС). It is also used as antifriction and hydrophobic material.

6. Polymethyl methacrylate (plexiglass) - applied in electrical engineering as a design material.

7. Polyamide - has high strength, wear resistance, high dielectric properties.

8. Synthetic rubbers (elastomers).

9. Phenol formaldehyde resins - the basis of adhesives, varnishes, plastics.

10.5. Organic polymeric materials

10.5.1. Polymerization thermoplastic resins

Polypropylene- thermoplastic polymer derived from propylene gas C 3 H 6. (CH 2 \u003d CH - CH 3)

Structural formula

[-CH 2 -CH (CH 3) -] n.

Polymerization is conducted in gasoline at a temperature of 70 ° C by the method of Natta. The polymer with a regular structure is obtained. It has a high chemical resistance and is destroyed only under the action of 98% H 2 SO 4 and 50% HNO 3 at temperatures above 70 °.

Electrical properties like polyethylene. The film has a small gas - and vapor permeability. It is used for insulation of high-frequency cables and mounting wires, as a dielectric of high-frequency capacitors.

Polyisobutylene- Product of polymerization of gas isobutylene. Structural formula:

There are several types of polyisobutylene, liquid low molecular weight (1000) and solid high molecular weight (400000). Those. Depending on the degree of polymerization, it can be liquid with different viscosity and elastic like rubber. Molecules have a filamental symmetrical structure with branching in lateral groups. This can explain the stickiness of the material, large elasticity, compared with polyethylene. This is a dielectric with ρ \u003d 10 15 - 10 16 Ω cm, ε \u003d 2.25 - 2.35, electric strength - 16 - 23 kV / mm.

The frost resistance of polyisobutylene depends on its molecular weight than the weight is greater, the more polyisobutylene is frosty.

In pure form or in the compositions, polyisobutylene is used for the manufacture of insulating tapes; isolation of high-frequency cables (in compositions with polyethylene); seals; insulating fillings compounds; Adhesive materials.

Due to the cold fluidity of polyisobutylene for isolation of high-frequency cables, a rubber-like mixture of 90% polyisobutylene and 10% polystyrene with a layer of polystyrene film (styroflex) is used. This mixture has high electrical properties with high humidity.

Polystyrene.- Polymerization product of styrene - unsaturated HC - VinylBenzene or phenylethylene -CH 2 CHC 6 H 5.

Styrene molecule is somewhat asymmetrical, due to the presence of phenolic groups in it.

At normal temperature, styrene is a colorless transparent liquid. From the methods of styrene polymerization and the production of solid dielectric, the methods of block and emulsion polymerization are most common.

Styrene toxic, causes irritation of the skin, eyes and respiratory organs. Polystyrene dust forms explosive concentrations with air.

Density - 1.05 g / cm 3

ρ , Ohm · cm, 10 14 - 10 17

ε \u003d 2.55 - 2.52

Polystyrene - chemically racks, concentrated acids (HNO 3 - exception) and alkali do not act on it, it dissolves in ether, ketones, aromatic hydrocarbons and does not dissolve in alcohols, water, vegetable oils.

The degree of polymerization depends on the conditions. You can get a polymer with a molecular weight up to 600,000. These will be solid polymers. The use of polymers with M.M. From 40,000 to 150000. When heated 180 - 300 ºС, depolymerization is possible. Electrical properties also depend on the polymerization method and the presence of polar impurities, especially emulsifiers.

Polystyrene products produce pressing and injection molding. It is made of: film (styrooflex), lamp panels, coil frames, insulating parts of switches, antennas insulators; Films for capacitors and other polystyrene in the form of ribbons, washers, caps are used for insulation of high-frequency cables.

Disadvantages: low heating resistance and inclination to rapid aging - the appearance on the surface of the grid of small cracks; This reduces the electrical strength and increases ε.

Polydichlorestyrol- differs from polystyrene in each link of the chain of two chlorine atoms and as a result of this, a large heat resistance, heating.

ε \u003d 2.25 - 2.65

Polychlorvinyl- Thermoplastic synthetic high-polymer compound with the linear structure of molecules of the asymmetric structure. A sharply pronounced asymmetry and polarity of polychlorvinyl is associated with chlorine.

Obtained by polymerization of chlorvinyl H 2 C \u003d CH -Cl. The initial raw material for obtaining is dichloroethane and acetylene. Chlorvinyl is a halogen derivative of ethylene. At normal temperature, it is a colorless gas, at a temperature of 12-14 ºС - liquid, and at -159 ºС solid. Chlorvinyl polymerization can be produced in three ways: block, emulsion and solutions. The most applicable is a water-emulsion. There are brands of polychlorvinyl with additive plasticizers and fillers with various mechanical properties, frost resistance and heating resistance.

Polychlorvinyl molecule has the view

ε \u003d 3.1 - 3.4 (at 800 Hz)

ρ = 10 15 - 10 16 ohms. cm

Polychlorvinyl minorgroscopic, a change in dielectric properties in a humid atmosphere is insignificant.

Products are made by pressing, injection molding, stamping, molding.

Polychlorvinyl is used in the form of plastics of various elasticity, in the form of varnishes for protective coatings. It is chemically racks against the effects of alkalis, acids, alcohol, gasoline and mineral oils. Esters, ketones, aromatic hydrocarbons partially dissolve it or cause swelling.

Polychlorvinyl is used in the electric industry in the following products:

a) rechargeable banks;

b) hoses for electrical insulation and chemical protection;

c) isolation of telephone wires and cables (lead substitute);

d) insulating gaskets, sleeves and other products.

It does not apply in high-frequency circuits as a dielectric due to high dielectric losses (high conductivity), and at temperatures above 60-70 ºС.

Polyvinilacetate- polymers of liquid vinyl acetate obtained as a result of chemical interaction of acetylene (C 2 H 2) and acetic acid:

or CH 2 \u003d Chococh 3. From it receive vinilacetate- Colorless lightweight liquid with an essential smell, decomposed at 400 ° C.

Material polyvinilacetate- Colorless, odorless, occupies the middle place between the resins and rubber. Properties depend on the degree of polymerization. MM From 10,000 to 100000. The softening temperature is 40 - 50 ° C.

High polimic products at 50 - 100 ° C become rubber-like, and at negative temperatures - solid, rather elastic.

All polymers have light-resistance, even at 100 ° C. When heated, the polyvinyl acetate is not depolymerized to the monomer, and decomposes with the cleavage of acetic acid. Not flammable. This is a polar polymer. Soluble in ether, ketones (acetone), methyl (CH 3 OH) and ethyl (C 2 H 5 OH) alcohols, not soluble in gasoline. Water swells slightly, but does not dissolve.

It is mainly used for the production of suspected glass "Triplex". It is used in electrical insulating technology. Lucky on its basis are valued for good electrical insulating properties, elasticity, light-resistance, colorlessness.

Polymethyl methacrylate(organic glass, plexiglass) - a large group of high-fat ethers of methacrylic acid having a large technical application

In the electrical industry, it is used as auxiliary material.

It is obtained with the polymerization of methacrylic acid methacrylic ester (methyl methacrylate) in the presence of the initiator.

At 573 to polymethyl methacrylate, depolymerizes with the formation of the initial metomer methyl methacrylate.

In the composition of the polyvinyl acetate, it is distinguished by the presence of a methyl group in the side chain instead of hydrogen and the presence of valence bond of carbon main chain with an ether group not through oxygen, but through carbon.

Has low heat resistance (approximately 56 ° C); ε \u003d 3.3 - 4.5; ρ. \u003d 2.3 · 10 13 - 2 · 10 12 Ohm. m. Not suitable for electrical insulation.

It is used as a structural, optical and decorative material painted by aniline dyes in various colors. From it, the housings and scales of the instruments are made, transparent protective glasses and caps, transparent parts of the equipment, etc. Organic glass is easily processed: dried, sawed, it is cut, polished, polished. It sounds well, stamps and glued with solutions of polymethyl methacrylate in dichloroethane.

Polyvinyl alcohol- solid polymer composition (-CH 2 -Choh-) N. It turns out in the hydrolysis of polyvinyl acetate with acid or alkali. Polyvinyl alcohol formula

Linear polymer asymmetric structure. The presence of a group, it defines high hygroscopicity and polarity of alcohol in each chain link. Dissolves only in water. Hasρ \u003d 10 7 Ohm · cm. Used as auxiliary material in the manufacture of printed radioshem.

Resistant to mold and bacteria. Good material for the manufacture of oil and benzustable membranes, hoses, panels. Warming at 170 ° C for 3 to 5 hours increases water resistance and reduces the solubility of polyvinyl alcohol.

Oligoefirarilat

Oligomers- Chemical compounds with medium molecular weight (less than 1000), large compared to monomers and less compared to polymers. The main property is the ability to polymerization due to unsaturated bonds that determine the spatial or linear structure of the finished product. During polymerization, low molecular weight products are not distinguished, so insulation obtained by filling with oligomers differs in monolithium, without voids and pores. They do not require special conditions for the polymerization (high pressure, temperature, medium, etc.).

The industry produces polyester, polyurethane, silicone oligomeric compounds and modifications.

If the link between macromolecules is carried out using the weak forces of Van der Waals, they are called thermoplastics, if using chemical ties - Reactoplasts. Linear polymers include, for example, cellulose, to branched, for example, amylopectin, there are polymers with complex spatial three-dimensional structures.

In the structure of the polymer, a monomeric link can be isolated - a repeating structural fragment comprising several atoms. The polymers consist of a large number of repeated groups (links) of the same structure, such as polyvinyl chloride (-CH 2 -ChCl-) N, natural rubber, etc. High molecular compounds, which contain several types of repeated groups, are called copolymers or heteropolymers.

The polymer is formed from monomers as a result of polymerization or polycondensation reactions. Polymers include numerous natural connections: proteins, nucleic acids, polysaccharides, rubber and other organic matter. In most cases, the concept refers to organic compounds, but there are many inorganic polymers. Big number Polymers are obtained by synthetic by the simplest compounds of natural origin elements by the reactions of polymerization, polycondensation and chemical transformations. The names of the polymers are formed from the name of the monomer with the console pol-: Polethylene, polypropylene, polyvinyl acetate, etc.

Features

Special mechanical properties

• elasticity - the ability to high reversible deformations with a relatively small load (rubber);
• small fragility of glassy and crystalline polymers (plastics, organic glass);
• the ability of macromolecules to orientation under the action of a directional mechanical field (used in the manufacture of fibers and films).

Features of polymers solutions:

• high viscosity of the solution at low polymer concentration;
• the dissolution of the polymer occurs through the step of swelling.

Special chemical properties:

• the ability to change their physico-mechanical properties Under the influence of small amounts of reagent (rubber vulcanization, leather tanning, etc.).

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

Copolymers

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

Copolymers differ in structure, manufacturing technologies and properties. For 2014, technologies have been created:

• statistical copolymers formed by chains containing chemical groups various nature, it is obtained by the polymerization of a mixture of several source monomers;
• alternating copolymers are characterized by chains in which radicals of different monomers alternate;
• popular copolymers are formed by attaching the chains of the second monomer molecules on the side of macromolecules formed from the main monomer;
• comb-shaped copolymers call graft copolymers with very long side chains;
• the block copolymers are built of sufficiently extended chains (blocks) of one monomer, connected at the ends with sufficiently extended chains of another monomer.

Properties of copolymers

Comb-like copolymers can be made from materials with different propertiesWhat gives such a copolymer fundamentally new properties, such as liquid crystal.

In block copolymers composed of a component with different properties, the superlattices arise, built from the blocks distinguished in a separate phase chemical nature. The size of the blocks depend on the ratio of the initial monomers. Thus, a fragile polystyrene is added to stretching resistance to 40% by copolymerization with 5-10% polybutadiene, and a shockproof polystyrene is obtained, and with 19% polystyrene in polybutadiene, the material demonstrates rubber-like behavior.

Classification

By chemical composition All polymers are divided into organic, elementodorganic, inorganic.

• Organic polymers.
• Elementorganic polymers. They contain inorganic atoms (Si, Ti, Al) in the main chain of organic radicals, combined with organic radicals. There are no them in nature. Artificially obtained representative - silicone compounds.
• Inorganic polymers. They do not contain in a repeating link c-C connectionsBut able to contain organic radicals as side substituents.

It should be noted that the technique of polymers are often used as components of composite materials, such as fiberglass. Composite materials are possible, all the components of which are polymers (with different composition and properties).

In the form of macromolecules, polymers are divided into linear, branched (private case - star-shaped), tape, flat, comb-shaped, polymer mesh and so on.

Polymers are divided according to polarity (affecting solubility in various liquids). The polarity of the polymer units is determined by the presence of dipoles in their composition - molecules with a separated distribution of positive and negative charges. In non-polar units dipole moments Atom bonds are mutually compensated. Polymers whose links have significant polarity, called hydrophilic or polar. Polymers with non-polar links - notolar, hydrophobic. Polymers containing both polar and non-polar links are called amphilines. Homopolymers, each link which contains both polar and non-polar large groups, proposed to call amphilic homopolymers.

In relation to heating, the polymers are divided into thermoplastic and termoreactive. Thermoplastic Polymers (polyethylene, polypropylene, polystyrene) are softened during heating, they even melted, and when cooled solidified. This process is reversible. Termoreactive Polymers when heated is irreversible chemical destruction without melting. Thermoreactive polymers molecules have a nonlinear structure obtained by crosslinking (for example, vulcanization) of chain polymer molecules. Elastic properties Thermoreactive polymers are higher than that of thermoplastics, however, thermosactive polymers practically do not have the fluidity, as a result of which have a lower destruction voltage.

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

Types

Synthetic polymers. Artificial polymeric materials

A person has long been using natural polymeric materials in his life. It is the skin, fur, wool, flip, cotton, etc., used for the manufacture of clothing, various binders (cement, lime, clay), forming three-dimensional polymeric bodies with appropriate treatment, widely used as building materials. but industrial production Chain polymers began at the beginning of the 20th century, although the prerequisites for this appeared earlier.

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

In the first case, large-tonnage production is based on cellulose. The first polymeric material from physically modified cellulose - celluloid - was obtained in the middle of the XIX century. Large-scale production of simple and esters of cellulose was organized before and after the Second World War and exist to date. On their basis, films, fibers, paint materials and thickeners produce. It should be noted that the development of cinema and photographs were possible only due to the appearance transparent film From nitrocellulose.

The production of synthetic polymers began in 1906, when Leo Belland patented the so-called bakelite resin - the product of the condensation of phenol and formaldehyde, which turns into a three-dimensional polymer. For decades, it was used for the manufacture of electrical instruments, batteries, televisions, sockets, etc., and is currently more often used as a binder and adhesive substance.

The list is closed by the so-called unique polymers synthesized in the 60-70 years of the XX century. These include aromatic polyamides, polyimides, polyesters, polyester-ketones, etc.; indispensable attribute These polymers are the presence of aromatic cycles and (or) aromatic condensed structures. They are characterized by a combination of outstanding strength and heat resistance.

Fireproof polymers

Many polymers, such as polyurethanes, polyester and epoxy resins, tend to ignition, which is often unacceptable when practical application. To prevent this, various additives are applied or halogenated polymers are used. Halogenated unsaturated polymers are synthesized by inclusion in the condensation of chlorinated or brominated monomers, for example, hexachacid (HCHEMTFC), dibromneopentyl glycol or tetrabrombalic acid. The main disadvantage of such polymers is that when combustion, they are able to allocate gases that cause corrosion, which can be destructively affecting a nearby electronics.

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

Ammonium pyrophosphate acts on another principle: it causes charring that, together with a glass-like layer of pyrophosphates, isolating plastic from oxygen, inhibiting the spread of fire.