Polymers

Special mechanical properties

• elasticity - the ability to high reversible deformations at a relatively small load (rubbers);
• low fragility of glassy and crystalline polymers (plastics, organic glass);
• the ability of macromolecules to orient themselves under the action of a directed mechanical field (used in the manufacture of fibers and films).

Features of polymer solutions:

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

Special chemical properties:

• the ability to dramatically change their physical and mechanical properties under the influence of small amounts of reagent (vulcanization of rubber, tanning of leathers, etc.).

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

Polymers made from different monomers or chemically bonded molecules of different polymers are called copolymers. For example, high impact polystyrene is a polystyrene – polybutadiene copolymer ^[3] .

The copolymers vary in structure, manufacturing technology and obtained properties. In 2014, technologies were created ^[3] :

• statistical copolymers formed by chains containing chemical groups of various nature are obtained by polymerization of a mixture of several starting monomers;
• alternating copolymers are characterized by chains in which radicals of different monomers alternate;
• grafted copolymers are formed by attaching side chains of the molecules of the second monomer to the side to macromolecules formed from the main monomer;
• grafted copolymers are called grafted copolymers with very long side chains;
• block copolymers are constructed from sufficiently long chains (blocks) of one monomer, connected at the ends with sufficiently long chains of another monomer.

Copolymer Properties

Comb-like copolymers can be composed of materials with different properties, which gives such a copolymer fundamentally new properties, for example, liquid crystalline ^[3] .

In block copolymers composed of components with different properties, superlattices arise, which are built up of blocks of different chemical nature that are separated into a separate phase. The sizes of the blocks depend on the ratio of the starting monomers. So, brittle polystyrene is added to tensile strength up to 40% by copolymerization with 5-10% polybutadiene, and high-impact polystyrene is obtained, and at 19% polystyrene in polybutadiene the material exhibits rubber-like behavior ^[3] .

According to the chemical composition, all polymers are divided into organic , organoelemental , inorganic .

• Organic polymers.
• Organoelement polymers. They contain inorganic atoms ( Si , Ti , Al ) combined with organic radicals in the main chain of organic radicals. In nature, they are not. An artificially obtained representative is organosilicon compounds.
• Inorganic polymers . They do not contain C - C bonds in the repeating unit, but they are able to contain organic radicals , like side substituents.

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

In the form of macromolecules, polymers are divided into linear, branched (star-shaped special cases), ribbon, flat, comb-like, polymer networks and so on.

Polymers are divided by 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 disconnected distribution of positive and negative charges. In nonpolar links, the dipole moments of atomic bonds are mutually compensated. Polymers whose units have significant polarity are called hydrophilic or polar . Polymers with non-polar units - non - polar , hydrophobic . Polymers containing both polar and non-polar units are called amphiphilic . Homopolymers, each link of which contains both polar and nonpolar large groups, are proposed to be called amphiphilic homopolymers .

In relation to heating, polymers are divided into thermoplastic and thermosetting . Thermoplastic polymers ( polyethylene , polypropylene , polystyrene ) soften when heated, even melt, and harden when cooled. This process is reversible. When heated, thermosetting polymers undergo irreversible chemical destruction without melting. Molecules of thermosetting polymers have a nonlinear structure, obtained by crosslinking (for example, vulcanization ) of chain polymer molecules. The elastic properties of thermosetting polymers are higher than those of thermoplastics, however, thermosetting polymers practically do not have flowability, as a result of which they have a lower fracture stress.

Natural organic polymers are formed in plant and animal organisms. The most important of them are polysaccharides , proteins and nucleic acids , of which the bodies of plants and animals are largely composed and which ensure the very functioning of life on Earth. It is believed that the decisive stage in the emergence of life on Earth was the formation of more complex, high molecular molecules from simple organic molecules (see Chemical evolution ).

Synthetic polymers. Artificial Polymer Materials

Man has long been using natural polymeric materials in his life. These are leather , furs , wool , silk , cotton , etc., used for making clothes, various binders ( cement , lime , clay ), which, when processed appropriately, form three-dimensional polymer bodies that are widely used as building materials . However, the industrial production of chain polymers began at the beginning of the 20th century, although the prerequisites for this appeared earlier.

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

In the first case, large-capacity production is based on cellulose . The first polymer material from physically modified cellulose - celluloid - was obtained back in the middle of the XIX century. The large-scale production of cellulose ethers and esters was organized before and after World War II and exists to this day. Based on them, films , fibers , coatings and thickeners are produced. It should be noted that the development of cinema and photography was possible only thanks to the appearance of a transparent film of nitrocellulose .

The production of synthetic polymers began in 1906, when Leo Bakeland patented the so-called Bakelite resin, a product of the condensation of phenol and formaldehyde , which turns into a three-dimensional polymer when heated. For decades, it has been used for the manufacture of cases of electrical devices, batteries , televisions , sockets, etc., and is now more often used as a binder and adhesive .

Thanks to the efforts of Henry Ford , before the First World War the rapid development of the automotive industry began, first on the basis of natural, then also synthetic rubber . Production of the latter was mastered on the eve of World War II in the Soviet Union, England, Germany and the USA. In the same years, the industrial production of polystyrene and polyvinyl chloride , which are excellent electrically insulating materials, as well as polymethyl methacrylate , was mastered - without the use of organic glass under the name “Plexiglass” mass aircraft construction would have been impossible during the war years.

After the war, the production of polyamide fiber and fabrics ( nylon , nylon ), which had begun before the war, resumed. In the 50s of the XX century, polyester fiber was developed and the production of fabrics based on it under the name lavsan or polyethylene terephthalate was mastered. Polypropylene and nitron - artificial wool made of polyacrylonitrile - close the list of synthetic fibers that modern man uses for clothing and production activities. In the first case, these fibers are very often combined with natural fibers from cellulose or from protein ( cotton , wool , silk ). An epoch-making event in the world of polymers was the discovery in the mid-1950s and the rapid industrial development of Ziegler-Natta catalysts , which led to the emergence of polymeric materials based on polyolefins and, above all, low-pressure polypropylene and polyethylene (before that, the production of polyethylene at a pressure of the order of 1000 atm.), as well as stereoregular polymers capable of crystallization. Then, polyurethanes — the most common sealants, adhesive and porous soft materials (foam rubber), and polysiloxanes — organoelemental polymers with higher heat resistance and elasticity compared to organic polymers — were introduced into mass production.

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 .; an indispensable attribute of these polymers is the presence of aromatic rings and (or) aromatic condensed structures in them. They are characterized by a combination of outstanding values ​​of strength and heat resistance.

Refractory Polymers

Many polymers, such as polyurethanes, polyester and epoxy resins, are prone to ignition, which is often unacceptable in practical applications. To prevent this, various additives are used or halogenated polymers are used. Halogenated unsaturated polymers are synthesized by incorporation into the condensation of chlorinated or brominated monomers, for example, hexachlorodomethylene tetrahydrophthalic acid (GHEMTFC), dibromneopentyl glycol or tetrabromophthalic acid. The main disadvantage of such polymers is that, when burned, they are capable of emitting gases that cause corrosion, which can be detrimental to nearby electronics.

The action of aluminum hydroxide is based on the fact that under high-temperature exposure, water is released that prevents combustion. To achieve the effect, it is necessary to add large quantities of aluminum hydroxide: by weight of 4 parts to one part of unsaturated polyester resins.

Ammonium pyrophosphate acts on a different principle: it causes carbonization, which, together with a glassy layer of pyrophosphates, isolates the plastic from oxygen, inhibiting the spread of fire.

Polymerization is the process of combining many small molecules, known as monomers, into a covalently linked chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This occurs during the polymerization of PET polyester . Monomers are terephthalic acid (HOOC - C ₆ H ₄ - COOH) and ethylene glycol (HO - CH ₂ - CH ₂ - OH), but the repeating unit is - OC - C ₆ H ₄ - COO - CH ₂ - CH ₂ - O - , which corresponds to a combination of two monomers with the loss of two water molecules. A separate fragment of each monomer, which is included in the polymer, is known as a compound.

Laboratory synthesis methods are usually divided into two categories: stepwise polymerization and chain polymerization ^[4] . A significant difference between them is that during polymerization with chain growth, the monomers are added to the chain only one each ^[5] , for example, in polyethylene , while during step polymerization, the monomer chains can be connected directly to each other ^[6] , for example, in polyester . More modern methods, such as plasma polymerization, do not fit into any of the categories. Synthetic polymerization reactions can be carried out with or without a catalyst . Laboratory synthesis of biopolymers, especially proteins, is an area of ​​intensive research.

Due to its valuable properties, polymers are used in mechanical engineering , textile industry , agriculture , medicine , automobile - and shipbuilding , aircraft manufacturing and in everyday life (textile and leather products, dishes, glue and varnishes , jewelry and other items). Based on high molecular weight compounds, rubber , fiber , plastics , films and coatings are made. All tissues of living organisms are high molecular weight compounds.

Наука о полимерах стала развиваться как самостоятельная область знания к началу Второй мировой войны и сформировалась как единое целое в 50-х годах XX столетия, когда была осознана роль полимеров в развитии технического прогресса и жизнедеятельности биологических объектов. Она тесно связана с физикой , физической , коллоидной и органической химией и может рассматриваться как одна из базовых основ современной молекулярной биологии , объектами изучения которой являются биополимеры .

• Пластмассы
• Мономер
• Макромолекула
• Полимеризация
• Поликарбонаты
• Крейзинг полимеров
• Супрамолекулярная химия
• Виниловые полимеры
• Биоразлагаемые полимеры
• Блок-сополимер
• Олигомер
• Химия полимеров

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• Волынский, Александр Львович. Как смешать полимеры? // Природа . — 2014. — № 3. — С. 44−52.
• Коршак В. В., Виноградова С. В. Равновесная поликонденсация. , М.: Наука, 1968.
• Коршак В. В., Виноградова С. В. Неравновесная поликонденсация. , М.: Наука, 1972.
• Кривошей В. Н. Тара из полимерных материалов, М., 1990.
• Махлис Ф. А. Федюкин Д. Л., Терминологический справочник по резине, М., 1989.
• Тагер А. А. Физико-химия полимеров, М.: Научный мир, 2007.;
• Шефтель В. О. Вредные вещества в пластмассах, М., 1991.
• Энциклопедии полимеров, т. 1 — 3, гл. ed. В. А. Каргин, М., 1972—1977.