In 1833, J. Berzelius coined the term “polymerism,” which he used to name one of the types of isomerism. Such substances (polymers) had to have the same composition, but different molecular weights, such as ethylene and butylene. The conclusion of J. Berzelius does not correspond to the modern understanding of the term “polymer”, because true (synthetic) polymers were not yet known at that time. The first mentions of synthetic polymers date back to 1838 (polyvinylidene chloride) and 1839 (polystyrene).
Polymer chemistry arose only after A. M. Butlerov created the theory of the chemical structure of organic compounds and was further developed thanks to an intensive search for methods of synthesizing rubber (G. Bushard, W. Tilden, K. Harries, I. L. Kondakov, S. V. Lebedev) . Since the beginning of the 20s of the 20th century, theoretical ideas about the structure of polymers began to develop.
DEFINITION
Polymers- chemical compounds with high molecular weight (from several thousand to many millions), the molecules of which (macromolecules) consist of a large number of repeating groups (monomer units).
Classification of polymers
The classification of polymers is based on three characteristics: their origin, chemical nature and differences in the main chain.
From the point of view of origin, all polymers are divided into natural (natural), which include nucleic acids, proteins, cellulose, natural rubber, amber; synthetic (obtained in the laboratory by synthesis and having no natural analogues), which include polyurethane, polyvinylidene fluoride, phenol-formaldehyde resins, etc.; artificial (obtained in the laboratory by synthesis, but based on natural polymers) - nitrocellulose, etc.
Based on their chemical nature, polymers are divided into organic polymers (based on a monomer - an organic substance - all synthetic polymers), inorganic (based on Si, Ge, S and other inorganic elements - polysilanes, polysilicic acids) and organoelement (a mixture of organic and inorganic polymers – polysoxanes) of nature.
There are homochain and heterochain polymers. In the first case, the main chain consists of carbon or silicon atoms (polysilanes, polystyrene), in the second - a skeleton of various atoms (polyamides, proteins).
Physical properties of polymers
Polymers are characterized by two states of aggregation - crystalline and amorphous - and special properties - elasticity (reversible deformations under small loads - rubber), low fragility (plastics), orientation under the action of a directed mechanical field, high viscosity, and the dissolution of the polymer occurs through its swelling.
Preparation of polymers
Polymerization reactions are chain reactions that represent the sequential addition of molecules of unsaturated compounds to each other with the formation of a high molecular weight product - a polymer (Fig. 1).
Rice. 1. General scheme for polymer production
For example, polyethylene is produced by polymerization of ethylene. The molecular weight of the molecule reaches 1 million.
n CH 2 =CH 2 = -(-CH 2 -CH 2 -)-
Chemical properties of polymers
First of all, polymers will be characterized by reactions characteristic of the functional group present in the polymer. For example, if the polymer contains a hydroxo group characteristic of the class of alcohols, therefore, the polymer will participate in reactions like alcohols.
Secondly, interaction with low molecular weight compounds, interaction of polymers with each other with the formation of network or branched polymers, reactions between functional groups that are part of the same polymer, as well as the decomposition of the polymer into monomers (destruction of the chain).
Application of polymers
The production of polymers has found wide application in various areas of human life - the chemical industry (plastic production), machine and aircraft construction, oil refining enterprises, medicine and pharmacology, agriculture (production of herbicides, insecticides, pesticides), construction industry (sound and thermal insulation), production of toys, windows, pipes, household items.
Examples of problem solving
EXAMPLE 1
EXAMPLE 1
| Exercise | Polystyrene is highly soluble in non-polar organic solvents: benzene, toluene, xylene, carbon tetrachloride. Calculate the mass fraction (%) of polystyrene in a solution obtained by dissolving 25 g of polystyrene in benzene weighing 85 g. (22.73%). |
| Solution | We write down the formula for finding the mass fraction:
Let's find the mass of benzene solution: m solution (C 6 H 6) = m (C 6 H 6)/(/100%) |
Classification by method of production (origin)
Flammability classification
Classification by behavior when heated
Classification of polymers according to the structure of macromolecules
CLASSIFICATION OF POLYMERS
Synthesis of polymers.
A polymer is a chemical substance that has a large molecular weight and consists of a large number of periodically repeating fragments linked by chemical bonds. These fragments are called elementary units.
Thus, the characteristics of polymers are as follows: 1. very high molecular weight (tens and hundreds of thousands). 2. chain structure of molecules (usually simple bonds).
It should be noted that polymers today successfully compete with all other materials used by humanity since ancient times.
Application of polymers:
Polymers for biological and medical purposes
Ion and electron exchange materials
Heat and heat resistant plastics
Insulators
Construction and structural materials
Surfactants and materials resistant to aggressive environments.
The rapid expansion of polymer production has led to the fact that their fire hazard (and all of them burn better than wood) has become a national disaster for many countries. When they burn and decompose, various substances are formed, mostly toxic to humans. Knowing the dangerous properties of the resulting substances is necessary to successfully combat them.
Classification of polymers according to the composition of the main chain of macromolecules (most common):
I. Carbon-chain IUDs - the main polymer chains are built only from carbon atoms
II. Heterochain BMCs - the main polymer chains, in addition to carbon atoms, contain heteroatoms (oxygen, nitrogen, phosphorus, sulfur, etc.)
III. Organoelement polymer compounds - the main chains of macromolecules contain elements that are not part of natural organic compounds (Si, Al, Ti, B, Pb, Sb, Sn, etc.)
Each class is divided into separate groups depending on the structure of the chain, the presence of bonds, the number and nature of substituents, and side chains. Heterochain compounds are classified, in addition, taking into account the nature and number of heteroatoms, and organoelement polymers - depending on the combination of hydrocarbon units with atoms of silicon, titanium, aluminum, etc.
a) polymers with saturated chains: polypropylene – [-CH 2 -CH-] n,
polyethylene – [-CH 2 -CH 2 -] n; CH 3
b) polymers with unsaturated chains: polybutadiene – [-CH 2 -CH=CH-CH 2 -] n;
c) halogen-substituted polymers: Teflon - [-CF 2 -CF 2 -] n, PVC - [-CH 2 -CHCl-] n;
d) polymer alcohols: polyvinyl alcohol – [-CH 2 -CH-] n;
e) polymers of alcohol derivatives: polyvinyl acetate – [-CH 2 -CH-] n;
f) polymeric aldehydes and ketones: polyacrolein – [-CH 2 -CH-] n;
g) polymers of carboxylic acids: polyacrylic acid – [-CH 2 -CH-] n;
h) polymer nitriles: PAN – [-CH 2 -CH-] n;
i) polymers of aromatic hydrocarbons: polystyrene – [-CH 2 -CH-] n.
a) polyethers: polyglycols – [-CH 2 -CH 2 -O-] n;
b) polyesters: polyethylene glycol terephthalate –
[-O-CH 2 -CH 2 -O-C-C 6 H 4 -C-] n;
c) polymer peroxides: polymer styrene peroxide – [-CH 2 -CH-O-O-] n;
2. Polymers containing nitrogen atoms in the main chain:
a) polymer amines: polyethylenediamine – [-CH 2 –CH 2 –NH-] n;
b) polymer amides: polycaprolactam – [-NН-(СH 2) 5 -С-] n;
3. Polymers containing both nitrogen and oxygen atoms in the main chain - polyurethanes: [-С-NН-R-NN-С-О-R-О-] n;
4.Polymers containing sulfur atoms in the main chain:
a) polythioethers [-(CH 2) 4 – S-] n;
b) polytetrasulfides [-(CH 2) 4 -S - S-] n;
5.Polymers containing phosphorus atoms in the main chain
for example: O
[- P – O-CH 2 -CH 2 -O-] n ;
1. Organosilicon polymer compounds
a) polysilane compounds R R
b) polysiloxane compounds
[-Si-O-Si-O-]n;
c) polycarbosilane compounds
[-Si-(-C-) n -Si-(-C-) n -] n ;
d) polycarbosiloxane compounds
[-O-Si-O-(-C-) n -] n ;
2. Organotitanium polymer compounds, for example:
OC 4 H 9 OC 4 H 9
[-O – Ti – O – Ti-] n ;
OC 4 H 9 OC 4 H 9
3. Organoaluminum polymer compounds, for example:
[-O – Al – O – Al-] n ;
Macromolecules can have a linear, branched and spatial three-dimensional structure.
Linear polymers consist of macromolecules with a linear structure; such macromolecules are a collection of monomer units (-A-) connected into long unbranched chains:
nA ® (…-A - A-…) m + (…- A - A -…) R + …., where (…- A - A -…) are polymer macromolecules with different molecular weights.
Branched polymers are characterized by the presence of side branches in the main chains of macromolecules, shorter than the main chain, but also consisting of repeating monomer units:
…- A – A – A – A – A – A – A- …
Spatial polymers with a three-dimensional structure are characterized by the presence of chains of macromolecules interconnected by forces of basic valencies using cross bridges formed by atoms (-B-) or groups of atoms, for example monomer units (-A-)
A – A – A – A – A – A – A –
A – A – A – A – A – A –
A – A – A – A – A – A -
Three-dimensional polymers with frequent cross-links are called network polymers. For three-dimensional polymers, the concept of a molecule loses its meaning, since in them individual molecules are connected to each other in all directions, forming huge macromolecules.
thermoplastic- polymers of linear or branched structure, the properties of which are reversible with repeated heating and cooling;
thermosetting- some linear and branched polymers, the macromolecules of which, when heated, as a result of chemical interactions occurring between them, are connected to each other; in this case, spatial network structures are formed due to strong chemical bonds. After heating, thermosetting polymers usually become infusible and insoluble - a process of irreversible hardening occurs.
This classification is very approximate, since the ignition and combustion of materials depend not only on the nature of the material, but also on the temperature of the ignition source, ignition conditions, shape of the product or structures, etc.
According to this classification, polymeric materials are divided into flammable, low-flammable and non-flammable. Of the combustible materials, those that are difficult to ignite are distinguished, and those that are difficult to burn are self-extinguishing.
Examples of combustible polymers: polyethylene, polystyrene, polymethyl methacrylate, polyvinyl acetate, epoxy resins, cellulose, etc.
Examples of fire-resistant polymers: PVC, Teflon, phenol-formaldehyde resins, urea-formaldehyde resins.
Natural (proteins, nucleic acids, natural resins) (animal and
plant origin);
Synthetic (polyethylene, polypropylene, etc.);
Artificial (chemical modification of natural polymers - ethers
cellulose).
Inorganic: quartz, silicates, diamond, graphite, corundum, carbine, boron carbide, etc.
Organic: rubbers, cellulose, starch, organic glass and
Polymers are high molecular weight compounds that consist of many monomers. Polymers should be distinguished from such a thing as oligomers, in contrast to which, when adding another numbered unit, the properties of the polymer do not change.
The connection between the monomer units can be carried out using chemical bonds, in which case they are called thermosets, or due to the force of intermolecular action, which is typical for the so-called thermoplastics.
The combination of monomers to form a polymer can occur as a result of a polycondensation or polymerization reaction.
There are many similar compounds found in nature, the most famous of which are proteins, rubber, polysaccharides and nucleic acid. Such materials are called organic.
Today, a large number of polymers are produced synthetically. Such compounds are called inorganic polymers. Inorganic polymers are produced by combining natural elements through polycondensation reactions, polymerization and chemical transformation. This allows you to replace expensive or rare natural materials, or create new ones that have no analogues in nature. The main condition is that the polymer does not contain elements of organic origin.
Inorganic polymers, due to their properties, have gained wide popularity. The range of their use is quite wide, and new areas of application are constantly being found and new types of inorganic materials are being developed.
Main characteristics
Today, there are many types of inorganic polymers, both natural and synthetic, which have different compositions, properties, scope of application and state of aggregation.
The current level of development of the chemical industry makes it possible to produce inorganic polymers in large volumes. To obtain such material it is necessary to create conditions of high pressure and high temperature. The raw material for production is a pure substance that is amenable to the polymerization process.
Inorganic polymers are characterized by the fact that they have increased strength, flexibility, are difficult to attack by chemicals and are resistant to high temperatures. But some types may be fragile and lack elasticity, but at the same time they are quite strong. The most famous of them are graphite, ceramics, asbestos, mineral glass, mica, quartz and diamond.
The most common polymers are based on chains of elements such as silicon and aluminum. This is due to the abundance of these elements in nature, especially silicon. The most famous among them are inorganic polymers such as silicates and aluminosilicates.
Properties and characteristics vary not only depending on the chemical composition of the polymer, but also on molecular weight, degree of polymerization, atomic structure and polydispersity.
Polydispersity is the presence of macromolecules of different masses in the composition.
Most inorganic compounds are characterized by the following indicators:
- Elasticity. A characteristic such as elasticity shows the ability of a material to increase in size under the influence of an external force and return to its original state after the load is removed. For example, rubber can expand seven to eight times without changing its structure or causing any damage. Returning the shape and size is possible by maintaining the location of the macromolecules in the composition; only their individual segments move.
- Crystal structure. The properties and characteristics of the material depend on the spatial arrangement of the constituent elements, which is called the crystal structure, and their interactions. Based on these parameters, polymers are divided into crystalline and amorphous.
Crystalline ones have a stable structure in which a certain arrangement of macromolecules is observed. Amorphous ones consist of macromolecules of short-range order, which have a stable structure only in certain zones.
The structure and degree of crystallization depends on several factors, such as crystallization temperature, molecular weight and concentration of the polymer solution.
- Glassiness. This property is characteristic of amorphous polymers, which, when the temperature decreases or the pressure increases, acquire a glassy structure. In this case, the thermal movement of macromolecules stops. The temperature ranges at which the glass formation process occurs depends on the type of polymer, its structure and the properties of the structural elements.
- Viscous flow state. This is a property in which irreversible changes in the shape and volume of a material occur under the influence of external forces. In a viscous flowing state, structural elements move in a linear direction, which causes a change in its shape.
Structure of inorganic polymers
This property is very important in some industries. It is most often used in the processing of thermoplastics using methods such as injection molding, extrusion, vacuum forming and others. In this case, the polymer melts at elevated temperatures and high pressure.
Types of inorganic polymers
Today, there are certain criteria by which inorganic polymers are classified. The main ones:
- nature of origin;
- types of chemical elements and their diversity;
- number of monomer units;
- polymer chain structure;
- physical and chemical properties.
Depending on the nature of origin, synthetic and natural polymers are classified. Natural ones are formed in natural conditions without human intervention, while synthetic ones are produced and modified in industrial conditions to achieve the required properties.
Today, there are many types of inorganic polymers, among which are the most widely used. This includes asbestos.
Asbestos is a fine-fiber mineral that belongs to the silicate group. The chemical composition of asbestos is represented by silicates of magnesium, iron, sodium and calcium. Asbestos has carcinogenic properties and is therefore very dangerous to human health. It is very dangerous for workers involved in its extraction. But in the form of finished products, it is quite safe, since it does not dissolve in various liquids and does not react with them.
Silicone is one of the most common synthetic inorganic polymers. It is easy to meet in everyday life. The scientific name for silicone is polysiloxane. Its chemical composition is a bond of oxygen and silicon, which gives silicone the properties of high strength and flexibility. Thanks to this, silicone is able to withstand high temperatures and physical stress without losing strength, maintaining its shape and structure.
Carbon polymers are very common in nature. There are also many species synthesized by humans in industrial conditions. Among natural polymers, diamond stands out. This material is incredibly durable and has a crystal clear structure.
Carbyne is a synthetic carbon polymer that has increased strength properties that are not inferior to diamond and graphene. It is produced in the form of black cloudberry with a fine crystalline structure. It has electrical conductivity properties, which increases under the influence of light. Able to withstand temperatures of 5000 degrees without losing properties.
Graphite is a carbon polymer whose structure is characterized by planar orientation. Because of this, the structure of graphite is layered. This material conducts electricity and heat, but does not transmit light. Its variety is graphene, which consists of a single layer of carbon molecules.
Boron polymers are characterized by high hardness, not much inferior to diamonds. Capable of withstanding temperatures of more than 2000 degrees, which is much higher than the boundary temperature of diamond.
Selenium polymers are a fairly wide range of inorganic materials. The most famous of them is selenium carbide. Selenium carbide is a durable material that appears in the form of transparent crystals.
Polysilanes have special properties that distinguish them from other materials. This type conducts electricity and can withstand temperatures up to 300 degrees.
Application
Inorganic polymers are used in almost all areas of our lives. Depending on the type, they have different properties. Their main feature is that artificial materials have improved properties compared to organic materials.
Asbestos is used in various fields, mainly in construction. Mixtures of cement and asbestos are used to produce slate and various types of pipes. Asbestos is also used to reduce the acidic effect. In light industry, asbestos is used to sew fire-fighting suits.
Silicone is used in various fields. It is used to produce tubes for the chemical industry, elements used in the food industry, and is also used in construction as a sealant.
In general, silicone is one of the most functional inorganic polymers.
Diamond is best known as a jewelry material. It is very expensive due to its beauty and difficulty of extraction. But diamonds are also used in industry. This material is necessary in cutting devices for cutting very durable materials. It can be used in its pure form as a cutter or as a spray on cutting elements.
Graphite is widely used in various fields; pencils are made from it, it is used in mechanical engineering, in the nuclear industry and in the form of graphite rods.
Graphene and carbyne are still poorly understood, so their scope of application is limited.
Boron polymers are used to produce abrasives, cutting elements, etc. Tools made from such material are necessary for metal processing.
Selenium carbide is used to produce rock crystal. It is obtained by heating quartz sand and coal to 2000 degrees. Crystal is used to produce high-quality tableware and interior items.
INORGANIC POLYMERS
They have an inorganic main chains and do not contain org. side radicals. The main chains are built from covalent or ionic-covalent bonds; in some N. p. the chain of ionic-covalent bonds can be interrupted by single coordination joints. character. Structural N. p. is carried out according to the same characteristics as org. or elementoorg. polymers (see High molecular weight compounds). Among natural N. p. the most. reticular ones are common and are part of most minerals of the earth's crust. Many of them form a type of diamond or quartz. The upper elements are capable of forming linear n.p. rows III-VI gr. periodic systems. Within groups, as the row number increases, the ability of elements to form homo- or heteroatomic chains decreases sharply. Halogens, as in org. polymers, play the role of chain termination agents, although all possible combinations of them with other elements can form side groups. Elements VIII gr. can be included in the main chain, forming a coordination. N. p. The latter, in principle, are different from org. coordination polymers, where is the coordination system bonds form only a secondary structure. Mn. or metal salts of variable valency macroscopically. St. you look like mesh N. p.
Long homoatomic chains (with degree of polymerization n >= 100) form only the elements of group VI - S, Se and Te. These chains consist of only backbone atoms and do not contain side groups, but the electronic structures of the carbon chains and the S, Se and Te chains are different. Linear carbon - cumulenes=C=C=C=C= ... and car-bin ChS =
SChS =
MF... (see Carbon); in addition, carbon forms two-dimensional and three-dimensional covalent crystals, respectively. graphite And diamond. Sulfur and tellurium form atomic chains with simple bonds and very high P. They have the character of a phase transition, and the temperature region of stability of the polymer has a smeared lower and well-defined upper boundary. Below and above these boundaries are stable, respectively. cyclical octamers and diatomic molecules.
Dr. elements, even the closest neighbors of carbon in psriodic. system-B and Si are no longer capable of forming homoatomic chains or cyclic. oligomers with n >= 20 (regardless of the presence or absence of side groups). This is due to the fact that only carbon atoms are capable of forming purely covalent bonds with each other. For this reason, binary heterochain n.p. type [HMPLH] are more common n(see table), where the M and L atoms form ionic-covalent bonds with each other. In principle, heterochain linear chains do not necessarily have to be binary: a regularly repeating section of the chain can. formed by more complex combinations of atoms. The inclusion of metal atoms in the main chain destabilizes the linear structure and sharply reduces i.
COMBINATIONS OF ELEMENTS FORMING BINARY HETEROCYNIC INORGANIC POLYMERS TYPE [HMMHLH] n(MARKED WITH A + SIGN)
* Also forms inorg. polymers of composition [CHVCHRH] n.
The peculiarities of the electronic structure of the main chains of homo-chain nucleotides make them very vulnerable to attack by nucleophiles. or electroph. agents. For this reason alone, chains containing as a component L or others adjacent to it in periodicity are relatively more stable. system. But these chains usually also need stabilization, in nature. N.P. is associated with the formation of network structures and with a very strong intermolecular. interaction side groups (including the formation of salt bridges), as a result of which the majority of even linear N. items are insoluble and macroscopic. St. you are similar to reticular N. p.
Practical Of interest are linear N. items, which are most common. degrees are similar to organic ones - they can exist in the same phase, aggregate or relaxation states, and form similar supermoles. structures, etc. Such nanoparticles can be heat-resistant rubbers, glasses, fiber-forming materials, etc., and also exhibit a number of properties that are no longer inherent in org. polymers. These include polyphosphazenes, polymeric sulfur oxides (with different side groups), phosphates, . Certain combinations of M and L form chains that have no analogues among org. polymers, for example with a wide conduction band and . Having a well-developed flat or space has a wide conduction band. structure. A common superconductor at temperatures near 0 K is the polymer [ЧSNЧ] X; at elevated temperatures, it loses superconductivity, but retains its semiconductor properties. High-temperature superconducting nanoparticles must have a ceramic structure, that is, they must contain oxygen in their composition (in the side groups).
Processing of nitrate into glass, fibers, ceramics, etc. requires melting, and this is usually accompanied by reversible depolymerization. Therefore, modifying agents are usually used to stabilize moderately branched structures in melts.
Lit.: Encyclopedia of Polymers, vol. 2, M., 1974, p. 363-71; Bartenev G.M., Ultra-strong and high-strength inorganic glasses, M., 1974; Korshak V.V., Kozyreva N.M., "Advances in Chemistry", 1979, v. 48, v. 1, p. 5-29; Inorganic polymers, in: Encyclopedia of polymer science and technology, v. 7, N.Y.-L.-Sydney, 1967, p. 664-91. S. Ya. Frenkel.
Chemical encyclopedia. - M.: Soviet Encyclopedia. Ed. I. L. Knunyants. 1988 .
See what "INORGANIC POLYMERS" are in other dictionaries:
Polymers whose molecules have inorganic main chains and do not contain organic side radicals (framing groups). In nature, three-dimensional network inorganic polymers are widespread, which in the form of minerals are part of... ...
Polymers that do not contain C C bonds in the repeating unit, but are capable of containing an organic radical as side substituents. Contents 1 Classification 1.1 Homochain polymers ... Wikipedia
Polymers whose molecules have inorganic main chains and do not contain organic side radicals (framing groups). Three-dimensional network inorganic polymers, which in the form of minerals are part of... ... are widespread in nature. encyclopedic Dictionary
Polymers with an inorganic (not containing carbon atoms) main chain of a macromolecule (See Macromolecule). Side (framing) groups are usually also inorganic; however, polymers with organic side groups are often also classified as H...
Polymers and macromolecules have inorganic Ch. chains and do not contain organic side chains. radicals (framing groups). Practical synthetic matters. polymer polyphosphonitrile chloride (polydichlorophasphazene) [P(C1)2=N]n. Others are obtained from it... ... Big Encyclopedic Polytechnic Dictionary
Polymers, molecules that have inorganic Ch. chains and do not contain organic. side radicals (framing groups). In nature, three-dimensional reticulated NPs are widespread, which in the form of minerals are included in the composition of the earth's crust (for example, quartz). IN… … Natural science. encyclopedic Dictionary
- (from poly... and Greek meros share part), substances whose molecules (macromolecules) consist of a large number of repeating units; The molecular weight of polymers can vary from several thousand to many millions. Polymers by origin... Big Encyclopedic Dictionary
Ov; pl. (unit polymer, a; m.). [from Greek polys numerous and meros share, part] High-molecular chemical compounds consisting of homogeneous repeating groups of atoms, widely used in modern technology. Natural, synthetic products... ... encyclopedic Dictionary
- (from the Greek polymeres consisting of many parts, diverse) chemical compounds with a high molecular weight (from several thousand to many millions), the molecules of which (macromolecules (See Macromolecule)) consist of a large number ... ... Great Soviet Encyclopedia
Organic polymers play a significant role in nature. In addition, they are widely used in industry. Next, the composition, properties, and use of organic polymers are considered.
Peculiarities
The materials under consideration consist of monomers represented by repeating fragments of a structure of several atoms. They are connected into three-dimensional structures or chains of branched or linear shape due to polycondensation or polymerization. They are often clearly visible in the structure.
It should be said that the term "polymers" refers mainly to organic options, although inorganic compounds also exist.
The principle of naming the materials under consideration is to attach the prefix poly to the name of the monomer.
The properties of polymers are determined by the structure and size of macromolecules.
In addition to macromolecules, most polymers include other substances that serve to improve functional characteristics by modifying properties. They are presented:
- stabilizers (prevent aging reactions);
- fillers (inclusions of different phase states that serve to impart specific properties);
- plasticizers (increase frost resistance, reduce processing temperature and improve elasticity);
- lubricants (allows you to avoid sticking of metal elements of equipment used in processing);
- dyes (serve for decorative purposes and to create markings);
- flame retardants (reduce the flammability of some polymers);
- fungicides, antiseptics, insecticides (give antiseptic properties and resistance to insects and fungal mold).
In the natural environment, the materials in question are formed in organisms.
In addition, there are compounds close to polymers in structure, called oligomers. Their differences consist in a smaller number of units and a change in the initial properties when one or more of them is removed or added, while the parameters of the polymers are preserved. In addition, there is no clear opinion regarding the relationship between these compounds. Some consider oligomers to be low-molecular-weight variants of polymers, while others consider them to be a separate type of compound that is not high-molecular-weight.
Classification
Polymers are differentiated by the composition of units into:
- organic;
- organoelement;
- inorganic.
The former serve as the basis for most plastics.
Substances of the second type include hydrocarbon (organic) and inorganic fragments in their units.
According to their structure they are differentiated into:
- options in which atoms of different elements are framed by organic groups;
- substances where carbon atoms alternate with others;
- materials with carbon chains framed by organoelement groups.
All types presented have main circuits.
The most common inorganic polymers are aluminosilicates and silicates. These are the main minerals of the planet's crust.
Based on their origin, polymers are classified into:
- natural;
- synthetic (synthesized);
- modified (modified variants of the first group).
The latter are divided according to the method of production into:
- polycondensation;
- polymerization
Polycondensation is the process of forming macromolecules from monomer molecules containing more than one functional group with the release of NH 3, water and other substances.
Polymerization refers to the process of forming macromolecules with multiple bonds from a monomer.
Classification by macromolecular structure includes:
- branched;
- linear;
- three-dimensional stitched;
- staircases
Based on their response to thermal effects, polymers are differentiated into:
- thermosetting;
- thermoplastic.
Substances of the first type are represented by spatial variants with a rigid frame. When heated, they undergo destruction and some catch fire. This is due to the equal strength of internal connections and chain connections. As a result, the thermal effect leads to the rupture of both chains and structure, therefore, irreversible destruction occurs.
Thermoplastic options are represented by linear polymers that soften reversibly when heated and harden when cooled. Their properties are then preserved. The plasticity of these substances is due to the rupture of intermolecular and hydrogen bonds of chains upon moderate heating.
Finally, according to their structural features, organic polymers are divided into several classes.
- Weak and non-polar thermoplastics. They are presented in variants with a symmetrical molecular structure or with weakly polar bonds.
- Polar thermoplastics. This type includes substances with an asymmetric molecular structure and their own dipole moments. They are sometimes called low-frequency dielectrics. Due to their polarity, they attract moisture well. Also, most of them are wettable. These substances also differ from the previous class in having lower electrical resistance. Moreover, many of the polar thermoplastics are characterized by high elasticity, chemical resistance, and mechanical strength. Additional processing allows these compounds to be converted into flexible rubber-like materials.
- Thermosetting polymers. As mentioned above, these are substances with a spatial system of covalent bonds. They differ from thermoplastic options in hardness, heat resistance and fragility, a higher elastic modulus and a lower coefficient of linear expansion. In addition, such polymers are not susceptible to conventional solvents. They serve as the basis for many substances.
- Laminated plastics. They are represented by layered materials made from resin-impregnated sheets of paper, fiberglass, wood veneer, fabric, etc. Such polymers are characterized by the greatest anisotropy of characteristics and strength. But they are of little use for creating objects of complex configuration. They are used in radio, electrical engineering, and instrument making.
- Metal-plastics. These are polymers that include metal fillers in the form of fibers, powders, and fabrics. These additives serve to impart specific properties: magnetic, improve damping, electrical and thermal conductivity, absorption and reflection of radio waves.
Properties
Many organic polymers have good electrical insulating parameters over a wide range of voltages, frequencies and temperatures, and at high humidity. In addition, they have good sound and heat insulation characteristics. Organic polymers are also usually characterized by high resistance to chemical attack and are not subject to rotting or corrosion. Finally, these materials have great strength at low density.
The examples above demonstrate characteristics common to organic polymers. In addition, some of them are distinguished by specific features: transparency and low fragility (organic glass, plastics), macromolecular orientation with directed mechanical influence (fibers, films), high elasticity (rubber), rapid change in physical and mechanical parameters under the influence of a reagent in small quantities. quantity (rubber, leather, etc.), as well as high viscosity at low concentrations, radio transparency, anti-friction characteristics, diamagnetism, etc.
Application
Due to the above parameters, organic polymers have a wide range of applications. Thus, the combination of high strength with low density makes it possible to obtain materials with high specific strength (fabrics: leather, wool, fur, cotton, etc.; plastics).
In addition to those mentioned, other materials are produced from organic polymers: rubbers, paints and varnishes, adhesives, electrical insulating varnishes, fibrous and film substances, compounds, binding materials (lime, cement, clay). They are used for industrial and domestic needs.
However, organic polymers have a significant practical disadvantage - aging. This term refers to a change in their characteristics and sizes as a result of physical and chemical transformations occurring under the influence of various factors: abrasion, heating, irradiation, etc. Aging occurs through certain reactions depending on the type of material and influencing factors. The most common among them is destruction, which implies the formation of lower molecular weight substances due to the rupture of the chemical bond of the main chain. Based on the reasons, destruction is divided into thermal, chemical, mechanical, photochemical.
Story
Polymer research began to develop by the 40s. XX century and emerged as an independent scientific field in the middle of the century. This was due to the development of knowledge about the role of these substances in the organic world and the identification of the possibilities of their use in industry.
At the same time, chain polymers were produced at the beginning of the 20th century.
By the middle of the century, they mastered the production of electrically insulating polymers (polyvinyl chloride and polystyrene) and plexiglass.
At the beginning of the second half of the century, the production of polymer fabrics expanded due to the return of previously produced materials and the emergence of new options. Among them are cotton, wool, silk, lavsan. During the same period, thanks to the use of catalysts, the production of low-pressure polyethylene and polypropylene and crystallizing stereoregular variants began. A little later, they mastered the mass production of the most famous sealants, porous and adhesive materials, represented by polyurethanes, as well as organoelement polymers, which differ from organic analogues in greater elasticity and heat resistance (polysiloxanes).
In the 60s - 70s. Unique organic polymers with aromatic components, characterized by high heat resistance and strength, were created.
The production of organic polymers is still intensively developing. This is due to the possibility of using cheap materials such as coal, associated gases from oil refining and production and natural gases, together with water and air as feedstock for most of them.