Polymeric materials - a high molecular chemical compounds that consist of numerous malomolekulyarnyh monomers (units) of the same structure.Often the polymers are used for the manufacture of the following monomer components: ethylene, vinyl chloride, vinildenhlorid, vinyl acetate, propylene, methylmethacrylate, tetrafluoroethylene, styrene, urea, melamine, formaldehyde, phenol.In this article, we consider that such polymeric materials as well as their chemical and physical properties, classification and types.
Types polymers
features of the molecules of the material is a high molecular weight, which corresponds to the following value: M & gt; 5 * 103.Compounds with a lower level of this parameter (M = 500-5000) called oligomers.At low molecular weight compounds is less than 500. The following types of polymeric materials: synthetic and natural.The latter usually referred natural rubber, mica, wool, asbestos, cellulose, etc. D. However, the basic synthetic polymers occupy space character, which is obtained by the process of chemical synthesis of compounds of low molecular level.Depending on the method of manufacturing high-molecular materials differing polymers that are or by polycondensation, or by addition reaction.
Polymerization
This process is an association of low molecular weight components in the high-yield with long chains.The amount of polymerization level - the number of "examples" in the molecules of the composition.The most common polymeric materials contain from one thousand to ten thousand of their units.By the polymerization, the following commonly used compounds: polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene, polystyrene, polybutadiene and others.
Polycondensation
This process is a step response, which is the compound or a large number of similar monomers, or a pair of different groups (Aand B) polycondensors (macromolecule) with simultaneous formation of these by-products: methyl alcohol, carbon dioxide, hydrogen chloride, ammonia, water and others. Using polycondensation prepared silicones, polysulfones, polycarbonates, aminoplast resins, phenolics, polyesters, polyamides and other polymeric materials.
polyaddition
Under this process refer to the formation of polymers in multiple reactions accession monomer components which comprise the limiting reaction association unsaturated monomers of groups (active cycles or double bond).In contrast to the polycondensation, polyaddition reaction proceeds without the generation of by-products.The major task of this technology is considered cured epoxy resins and the preparation of polyurethanes.
Classification polymers
The composition of all polymer materials are divided into inorganic, organic and organometallic.The first of these (silicate glass, mica, asbestos, ceramics and others.) Do not contain atomic carbon.They are the basis of the oxides of aluminum, magnesium, silicon and the like. D. Organic polymers comprise the most extensive class, they contain carbon, hydrogen, nitrogen, sulfur, oxygen and halogen.Organometallic polymeric materials - are compounds which have the main chains composed of, besides the above, and the atoms of silicon, aluminum, titanium and other elements that can be combined with organic radicals.The nature of such combinations do not occur.This is an extremely synthetic polymers.Typical representatives of this group are the compounds in the silicone-based backbone which is built from silicon and oxygen atoms.
To obtain polymers with desired properties is often used in the art are not "pure" substance, and combinations thereof with organic or inorganic components.A good example is the polymer building materials: metal-plastics, glass, polymer concrete.
structure polymers
originality of the properties of these materials due to their structure, which, in turn, is divided into the following types: linear, branched, linear, spatial with large molecular groups and very specific geometric structure and staircase.Let us briefly examine each of them.
Polymeric materials with linear branched structure other than the main chain molecules have side branches.Such polymers include polypropylene and polyisobutylene.
materials with a linear structure have long zigzag or twisted into a spiral chain.Their macromolecules primarily characterized by repetitions sites in one structural unit or group of units of the chemical chain.Polymers with a linear structure characterized by the presence of very long macromolecules with a significant difference between the nature of the links along the chain between them.It is meant and intermolecular chemical bonds.Macromolecules such material is very flexible.And this property is the basis of the polymer chains, which leads to a qualitatively new features: high flexibility, as well as the absence of fragility in the hardened state.
And now we learn that such polymeric materials with a spatial structure.These materials form by combining to each other macromolecules strong chemical bonds in the transverse direction.The result is a net-like structure, in which a non-uniform basis for the spatial grid.Polymers of this type have a higher heat resistance and rigidity than linear.These materials are the basis for many non-metallic construction materials.
molecules of polymer materials with a ladder structure is composed of a pair of chains which are connected by a chemical bond.These include silicone polymers that are characterized by high hardness, heat resistance, moreover, they do not react with organic solvents.
phase composition Polymer
These materials are systems that consist of amorphous and crystalline regions.The first one helps to reduce stiffness, makes elastic polymer that is capable of large deformations reversible.The crystalline phase contributes to increase their strength, hardness, elastic modulus, and other parameters, while minimizing the molecular flexibility substance.The ratio of the volume of all these areas to the total volume is called the degree of crystallization, wherein the maximum level (80%) are polypropylenes, fluoropolymers, high density polyethylenes.Less than the level of degree of crystallization have polyvinyl chloride, polyethylene of low density.
Depending on the behavior of the polymeric material upon heating, they are usually divided into thermoplastic and thermoset.
thermosetting polymers
These materials are primarily linear structure.When heated, they soften, but as a result of leakage in the chemical reactions on the spatial structure changes, and the substance transforms into a solid.Further, this quality is maintained.On this principle polymer composites.Subsequent heating of the substance is not softened, and only leads to its degradation.Ready thermosetting mixture does not dissolve or melt, so it is unacceptable for recycling.This type of silicone materials include epoxy, phenol-formaldehyde and other resins.
thermoplastic polymers
These materials when heated, first soften and then melt and subsequent cooling solidifies.Thermoplastic polymers when such processing do not undergo chemical changes.This makes the process completely reversible.Substances of this type have a linear or branched linear structure of macromolecules, among whom are a small force and there is absolutely no chemical bonds.These include polyethylenes, polyamides, polystyrenes, and others. Technology such thermoplastic polymeric materials involves their manufacture by injection molding in watercooled forms, pressing, extrusion, blow molding and other methods.
chemical properties
polymers may have called in the following states: solid, liquid, amorphous, crystalline phase, and highly elastic, viscous-flow and glass deformation.The widespread use of polymeric materials is due to their high resistance to aggressive environments such as strong acids and alkalis.They are not susceptible to electrochemical corrosion.Furthermore, with increasing molecular weight material is a decrease solubility in organic solvents.A polymer having a spatial structure, generally are not susceptible to said liquids.Physical properties
Most polymers are insulators, moreover, they are non-magnetic materials.Of all the structural materials used but they have the lowest thermal conductivity and maximum heat capacity, and thermal shrinkage (about twenty times greater than that of metal).The reason for the loss of tightness of the various seal assemblies under conditions of low temperature is the so-called vitrification rubber, as well as a dramatic difference between the coefficients of expansion of metal and rubber in the vitreous state.
mechanical properties
Polymer materials have a wide range of mechanical properties that are highly dependent on their structure.Besides this parameter, a great impact on the mechanical properties of the material may have a variety of external factors.These include temperature, frequency, duration, or rate of loading, form the stress state, the pressure, the nature of the environment, heat treating, and others. A feature of the mechanical properties of polymeric materials is their relatively high strength at very low stiffness (compared with metals).
polymers can be divided into solid, which corresponds to the modulus of elasticity E = 1-10 GPa (fiber, film, plastic), and soft elastomeric material a modulus of elasticity which is E = 1-10 MPa (rubber).Patterns and failure mechanism of both are different.
for polymeric materials are characterized by a pronounced anisotropy of properties, as well as decrease in strength, the development of creep under sustained loading condition.Together with this, they have relatively high resistance to fatigue.In comparison with metals, they are more strongly dependent on temperature mechanical properties.One of the main characteristics of polymeric materials is the deformability (ductility).According to this parameter in a wide temperature range taken to evaluate their basic operating and technological properties.
Polymeric materials for the floor
now consider one of the practical uses of polymers, revealing all possible range of these materials.These chemicals are widely used in construction, repair and finishing works, in particular in the coating of floors.The huge popularity is due to the characteristics of the substances they are resistant to abrasion, maloteploprovodny, have little water absorption, strong enough and firm, possess high qualities of paint.Production of polymeric materials can be divided into three groups: Linoleum (roll), tile products and mixtures for the device screed.Now a brief look at each of them.
Linoleum produced by various types of fillers and polymers.Their composition can also contain plasticizers, processing aids, and pigments.Depending on the type of polymer material, distinguish polyester (Phenol), polyvinyl chloride, rubber, and other coatings kolloksilinovye.Furthermore, the structure they are divided into baseless and with sound, insulating foundation unilamellar and multilamellar, with smooth and grooved fleecy and single- and multi-color.
tiling materials made of polymer-based components have a very low abrasion resistance, chemical resistance and durability.Depending on the type of raw material, this type of polymer products are divided into kumaronopolivinilhloridnye, coumarone, PVC, rubber, fenolitovye, asphalt tile, as well as chipboard and fibreboard.
Materials for screeds are the most convenient and hygienic to use, they are highly durable.These compounds can be divided into Polymer-, polymer and polyvinyl acetate.
