Most of today's building materials, medicines, fabrics, household items, packaging and consumables are polymers. This is a whole group of compounds that have characteristic distinguishing features. There are a lot of them, but despite this, the number of polymers continues to grow. After all, synthetic chemists annually discover more and more new substances. At the same time, it was the natural polymer that was of particular importance at all times. What are these amazing molecules? What are their properties and what are the features? We will answer these questions in the course of the article.
Polymers: general characteristics
From the point of view of chemistry, a polymer is considered to be a molecule having a huge molecular weight: from several thousand to millions of units. However, in addition to this feature, there are several more by which substances can be classified precisely as natural and synthetic polymers. This is:
- constantly repeating monomer units that are connected by different interactions;
- the degree of polymerase (i.e. the number of monomers) should be veryhigh, otherwise the compound will be considered an oligomer;
- certain spatial orientation of a macromolecule;
- a set of important physical and chemical properties that are unique to this group.
In general, a substance of a polymeric nature is quite easy to distinguish from others. One has only to look at his formula to understand it. A typical example is the well-known polyethylene, widely used in everyday life and industry. It is the product of a polymerization reaction in which the unsaturated hydrocarbon ethene or ethylene enters. The reaction in general form is written as follows:
nCH2=CH2→(-CH-CH-) , where n is the degree of polymerization of molecules, showing how many monomeric units are included in its composition.
Also, as an example, one can cite a natural polymer, which is well known to everyone, it is starch. In addition, amylopectin, cellulose, chicken protein and many other substances belong to this group of compounds.
Reactions that can form macromolecules are of two types:
- polymerization;
- polycondensation.
The difference is that in the second case, the interaction products are low molecular weight. The structure of the polymer can be different, it depends on the atoms that form it. Linear forms are often found, but there are also three-dimensional meshes, which are very complex.
If we talk about the forces and interactions that hold monomer units together, then we can identify several basic ones:
- Van Der Waalsstrength;
- chemical bonds (covalent, ionic);
- electrostatic interaction.
All polymers cannot be combined into one category, as they have a completely different nature, method of formation and perform different functions. Their properties also differ. Therefore, there is a classification that allows you to divide all representatives of this group of substances into different categories. It may be based on several signs.
Classification of polymers
If we take as a basis the qualitative composition of the molecules, then all the substances under consideration can be divided into three groups.
- Organic - these are those that include atoms of carbon, hydrogen, sulfur, oxygen, phosphorus, nitrogen. That is, those elements that are biogenic. There are many examples: polyethylene, polyvinyl chloride, polypropylene, viscose, nylon, natural polymer - protein, nucleic acids and so on.
- Organic elemental - those that include some extraneous inorganic and non-biogenic element. Most often it is silicon, aluminum or titanium. Examples of such macromolecules: organic glass, glass polymers, composite materials.
- Inorganic - the chain is based on silicon atoms, not carbon. Radicals can also be part of side branches. They were discovered quite recently, in the middle of the 20th century. Used in medicine, construction, engineering and other industries. Examples: silicone, cinnabar.
If you separate polymers by origin, you canselect three of their groups.
- Natural polymers, the use of which has been widely carried out since antiquity. These are such macromolecules, for the creation of which a person did not make any efforts. They are products of the reactions of nature itself. Examples: silk, wool, protein, nucleic acids, starch, cellulose, leather, cotton, etc.
- Artificial. These are macromolecules that are created by man, but based on natural analogues. That is, the properties of an already existing natural polymer are simply improved and changed. Examples: artificial rubber, rubber.
- Synthetic - these are polymers in the creation of which only a person participates. There are no natural analogues for them. Scientists are developing methods for the synthesis of new materials that would have improved technical characteristics. This is how synthetic polymer compounds of various kinds are born. Examples: polyethylene, polypropylene, viscose, acetate fiber, etc.
There is one more feature that underlies the division of the considered substances into groups. These are reactivity and thermal stability. There are two categories for this parameter:
- thermoplastic;
- thermoset.
The most ancient, important and especially valuable is still a natural polymer. Its properties are unique. Therefore, we will further consider this particular category of macromolecules.
Which substance is a natural polymer?
To answer this question, let's first look around us. What surrounds us?Living organisms around us that feed, breathe, reproduce, bloom and produce fruits and seeds. And what do they represent from a molecular point of view? These are connections like:
- proteins;
- nucleic acids;
- polysaccharides.
So, each of these compounds is a natural polymer. Thus, it turns out that life around us exists only due to the presence of these molecules. Since ancient times, people have used clay, building mixtures and mortars to strengthen and create a home, weave yarn from wool, and use cotton, silk, wool and animal skin to create clothes. Natural organic polymers accompanied man at all stages of his formation and development and in many ways helped him achieve the results that we have today.
Nature itself gave everything to make people's lives as comfortable as possible. Over time, rubber was discovered, its remarkable properties were clarified. Man has learned to use starch for food purposes, and cellulose for technical purposes. Camphor is also a natural polymer, which has also been known since ancient times. Resins, proteins, nucleic acids are all examples of compounds under consideration.
Structure of natural polymers
Not all representatives of this class of substances have the same structure. Thus, natural and synthetic polymers can differ significantly. Their molecules are oriented in such a way that it is most beneficial and convenient to exist from an energy point of view. At the same time, many natural species are able to swell and their structure changes in the process. There are several most common variants of the chain structure:
- linear;
- branched;
- star-shaped;
- flat;
- mesh;
- tape;
- comb-shaped.
Artificial and synthetic representatives of macromolecules have a very large mass, a huge number of atoms. They are created with specially specified properties. Therefore, their structure was originally planned by man. Natural polymers are most often either linear or reticulated in structure.
Examples of natural macromolecules
Natural and artificial polymers are very close to each other. After all, the first become the basis for the creation of the second. There are many examples of such transformations. Here are some of them.
- Ordinary milky-white plastic is a product obtained by treating cellulose with nitric acid with the addition of natural camphor. The polymerization reaction causes the resulting polymer to solidify and become the desired product. And the plasticizer - camphor, makes it able to soften when heated and change its shape.
- Acetate silk, copper-ammonia fiber, viscose are all examples of those threads, fibers that are obtained from cellulose. Fabrics made from natural cotton and linen are not so durable, not shiny, easily wrinkled. But the artificial analogues of them are devoid of these shortcomings, which makes their use very attractive.
- Artificial stones, building materials, mixtures, leather substitutes areSee also examples of polymers derived from natural raw materials.
The substance, which is a natural polymer, can also be used in its true form. There are also many such examples:
- rosin;
- amber;
- starch;
- amylopectin;
- cellulose;
- fur;
- wool;
- cotton;
- silk;
- cement;
- clay;
- lime;
- proteins;
- nucleic acids and so on.
Obviously, the class of compounds we are considering is very numerous, practically important and significant for people. Now let's take a closer look at several representatives of natural polymers, which are in great demand at the present time.
Silk and wool
The formula of natural silk polymer is complex, because its chemical composition is expressed by the following components:
- fibroin;
- sericin;
- waxes;
- fats.
The main protein itself, fibroin, contains several types of amino acids. If you imagine its polypeptide chain, then it will look something like this: (-NH-CH2-CO-NH-CH(CH3)- CO-NH-CH2-CO-)n. And this is only part of it. If we imagine that an equally complex sericin protein molecule is attached to this structure with the help of van der Waals forces, and together they are mixed into a single conformation with wax and fats, then it is clear why it is difficult to depict the formula of natural silk.
For todayToday, most of this product is supplied by China, because in its open spaces there is a natural habitat for the main producer - the silkworm. Previously, starting from the most ancient times, natural silk was highly valued. Only noble, rich people could afford clothes from it. Today, many characteristics of this fabric leave much to be desired. For example, it is highly magnetized and wrinkled, in addition, it loses its luster and fades from exposure to the sun. Therefore, artificial derivatives based on it are more in use.
Wool is also a natural polymer, as it is a waste product of the skin and sebaceous glands of animals. Based on this protein product, knitwear is made, which, like silk, is a valuable material.
Starch
Natural polymer starch is a waste product of plants. They produce it as a result of the process of photosynthesis and accumulate in different parts of the body. Its chemical composition:
- amylopectin;
- amylose;
- alpha-glucose.
The spatial structure of starch is very branched, disordered. Thanks to the amylopectin included in the composition, it is able to swell in water, turning into a so-called paste. This colloidal solution is used in engineering and industry. Medicine, the food industry, the manufacture of wallpaper adhesives are also areas of use for this substance.
Among plants containing the maximum amount of starch, we can distinguish:
- corn;
- potato;
- rice;
- wheat;
- cassava;
- oats;
- buckwheat;
- bananas;
- sorghum.
Based on this biopolymer, bread is baked, pasta is made, kissels, cereals and other food products are cooked.
Pulp
From the point of view of chemistry, this substance is a polymer, the composition of which is expressed by the formula (C6H5O 5) . The monomeric link in the chain is beta-glucose. The main sites of cellulose content are the cell walls of plants. That is why wood is a valuable source of this compound.
Cellulose is a natural polymer that has a linear spatial structure. It is used to produce the following types of products:
- pulp and paper products;
- faux fur;
- different types of artificial fibers;
- cotton;
- plastics;
- smokeless powder;
- film strips and so on.
Obviously, its industrial significance is great. In order for a given compound to be used in production, it must first be extracted from plants. This is done by long-term cooking of wood in special devices. Further processing, as well as the reagents used for digestion, vary. There are several ways:
- sulfite;
- nitrate;
- sodium;
- sulfate.
After this treatment, the product still containsimpurities. It is based on lignin and hemicellulose. To get rid of them, the mass is treated with chlorine or alkali.
There are no biological catalysts in the human body that could break down this complex biopolymer. However, some animals (herbivores) have adapted to this. They have certain bacteria in their stomach that do it for them. In return, microorganisms receive energy for life and habitat. This form of symbiosis is extremely beneficial for both parties.
Rubber
This is a natural polymer of valuable economic importance. It was first described by Robert Cook, who discovered it in one of his travels. It happened like this. Having landed on an island inhabited by natives unknown to him, he was hospitably received by them. His attention was attracted by local children who were playing with an unusual object. This spherical body kicked off the floor and bounced high up, then returned.
Having asked the local population about what this toy was made of, Cook learned that the juice of one of the trees, the hevea, hardens in this way. Much later it was found out that this is the rubber biopolymer.
The chemical nature of this compound is known - it is isoprene that has undergone natural polymerization. The rubber formula is (С5Н8) . Its properties that make it so highly regarded are as follows:
- elasticity;
- wear resistant;
- electrical insulation;
- water resistant.
However, there are also disadvantages. In the cold, it becomes brittle and brittle, and in the heat, it becomes sticky and viscous. That is why it became necessary to synthesize analogues of an artificial or synthetic base. Today, rubbers are widely used for technical and industrial purposes. The most important products based on them:
- rubbers;
- ebonites.
Amber
It is a natural polymer, because in its structure it is a resin, its fossil form. The spatial structure is a frame amorphous polymer. It is very flammable and can be ignited with a match flame. It has luminescence properties. This is a very important and valuable quality that is used in jewelry. Jewelry based on amber is very beautiful and in demand.
In addition, this biopolymer is also used for medical purposes. It is also used to make sandpaper, varnish coatings for various surfaces.
