The term "polymer" was offered in the 19th century for the name of substances which at the similar chemical composition have different molecular weight. Now polymers call special high-molecular structures which find broad application in the different industries of the equipment.
General information about polymers
Polymers call organic and inorganic matter which consists of the monomeric links united by means of coordination and chemical bonds in long macromolecules.
Polymer is considered high-molecular connection. The quantity of links in it is called extent of polymerization. She has to be rather great. In most cases the number of links is considered sufficient if at accession of the next monomeric link of property of polymer do not change.
To understand what is polymer, it is necessary to take into account how molecules in substances of this look communicate.
The molecular mass of polymers can reach several thousand and even millions of atomic units of mass.
Communication between molecules can be expressed by means of Van der Waals's forces; in this case polymer is called thermolayer. If the chemical bond, polymer is called reaktoplasty. Polymer can have linear structure (cellulose); branched out (amylopectin); or difficult spatial, that is three-dimensional.
By consideration of the structure of polymer allocate a monomeric link. So the repeating fragment of structure which consists of several atoms is called. A large number of the repeating links having the similar building is a part of polymers.
Formation of polymers from monomeric structures goes as a result of so-called reactions of polymerization or polycondensation. Refer a number of natural connections to polymers: nucleinic acids, proteins, polysaccharides, rubber. Considerable number of polymers receive by synthesis on the basis of the simplest connections.
Names of polymers are formed with use of the name of monomer which the prefix "weed-" joins: polypropylene, polyethylene, etc.
Approaches to classification of polymers
For systematization of polymers various options of classifications by various signs are used. It is possible to carry to them: structure, way of production or receiving, spatial form of molecules and so on.
In terms of features of the chemical composition polymers are subdivided on:
- inorganic;
- organic;
The biggest group – organic high-molecular compounds. These are rubbers, pitches, vegetable oils, other products of plant and animal origin. Molecules of such connections in the main chain have atoms of nitrogen, oxygen and other elements. Organic polymers are distinguished by ability to the return deformation.
Elementoorganichesky polymers allocate in special group. Chains of elementoorganichesky connections are the cornerstone sets of the radicals relating to inorganic type.
Inorganic polymers can not have as a part of the repeating carbon links. These polymeric connections in the main chain have oxides of metals (calcium, aluminum, magnesium) or silicon. They have no side organic groups. Communications in the main chains differ in high durability. Treat to this group: ceramics, quartz, asbestos, silicate glass.
In certain cases consider two big groups of high-molecular substances: carbon-chain and heterochain. At the first in the main chain only carbon atoms. At heterochain in the main chain there can be other atoms: they give to polymers special characteristics. Each of these two big groups has the fractional building: subgroups differ with the structure of a chain, number of deputies and their structure, quantity of side branches.
In a form of molecules polymers happen:
- linear;
- branched out (including star-shaped);
- flat;
- tape;
- polymeric grids.
Properties of polymeric connections
Refer to mechanical properties of polymers:
- special elasticity;
- low fragility;
- ability of macromolecules to be guided along lines of the directed field.
Solutions of polymers have rather high viscosity at small concentration of substance. At dissolution, polymers pass through a swelling stage. Polymers easily change the physical and chemical properties at action for them a small dose of reagent. The flexibility of polymers is explained by their considerable molecular weight and the chain building.
In the equipment polymeric materials quite often act as components of composite materials. An example – fibreglass. There are composite materials which components are polymers of the different building and properties.
Polymers can differ on polarity. This property affects solubility of substance in liquids. Those polymers where links have considerable polarity, are called hydrophilic.
Differences between polymers exist as well in relation to heating. Carry polystyrene, polyethylene, polypropylene to thermoplastic polymers. When heating these materials are softened and are capable even to melt. Cooling will lead such polymers to hardening. And here thermoreactive polymers in case of heating collapse in an irreversible way, passing a melting stage. This type of materials has the increased elasticity, but such polymers are not fluid.
In the nature organic polymers are formed in animal and vegetable organisms. In particular, these biological structures contain polysaccharides, nucleinic acids and proteins. Such components provide existence of life on the planet. It is considered to be that emergence of high-molecular connections became one of important stages of formation of life on Earth. Practically all fabrics of living organisms are connections of this type.
Among natural high-molecular substances a specific place is held by proteinaceous connections. These are "bricks" of which "base" of living organisms is under construction. Squirrels take part in the majority of biochemical reactions, they are responsible for work of the immune system, for fibrillation processes, formation of a muscle and bone tissue. Proteinaceous structures – a necessary element of a system of supply of an organism with energy.
Synthetic polymers
Broad industrial production of polymers began a little more than hundred years ago. However prerequisites for introduction into circulation of polymers appeared much earlier. Furs, leather, cotton, silk, wool belong to polymeric materials which the person uses in the life long ago. Binding materials are not less important in economic activity: clay, cement, lime; when processing these substances form the polymeric bodies which are widely applied in construction practice.
From the very beginning industrial production of polymeric connections went in two directions. The first assumes processing of natural polymers in artificial materials. The second way – receiving synthetic polymeric connections from low-molecular organic.
Use of artificial polymers
Large production of polymeric connections was initially based on receiving cellulose. Celluloid was received in the middle of the XIX century. Before World War II the production of air of cellulose is organized. On the basis of such technologies produce fibers, films, varnishes, paints. Development of the film industry and the practical photo became possible only on the basis of a transparent nitrocellulose film.
The contribution to production of polymers was made by Henry Ford: rapid development of automotive industry happened against the background of emergence of synthetic rubber which succeeded rubber natural. On the eve of World War II, production technologies of polyvinylchloride and polystyrene were developed. These polymeric materials began to be used widely as the isolating substances in electrical equipment. Receiving the organic glass which received the name "plexiglass" made possible mass aircraft construction.
After war unique synthetic polymers appeared: polyair and polyamides having thermal stability and high durability.
Some polymers have tendency to ignition that limits their application in life and the equipment. To prevent the undesirable phenomena, use special additives. Other way – synthesis of the so-called halogenated polymers. The lack of such materials is that at impact of fire on them these polymers can emit the gases causing destruction of electronics.
Polymers found the greatest application in the textile industry, mechanical engineering, agriculture, sudo-, the car - and aircraft industry. Polymeric materials in medicine are widely used.