A high molecular weight compound is ... Definition, composition, characteristics, properties

High molecular weight compounds are polymers that have a high molecular weight. They can be organic and inorganic compounds. Distinguish between amorphous and crystalline substances, which consist of monomer rings. The latter are macromolecules connected by chemical and coordination bonds. In simple terms, a high molecular weight compound is a polymer, that is, monomeric substances that do not change their mass when the same “heavy” substance is attached to them. Otherwise, we will talk about the oligomer.

What does high molecular weight science study?

Chemistry of high molecular weight polymers is the study of molecular chains consisting of monomeric subunits. This takes into account a huge area of ​​research. Many polymers have significant industrial and commercial value. In America, along with the discovery of natural gas, the launch of a major project to build a polyethylene plant began. Ethane is converted from natural gas to ethylene, a monomer from which polyethylene can be made.

A polymer as a high molecular weight compound is:

• Any of a class of natural or synthetic substances consisting of very large molecules called macromolecules.
• Many simpler chemical units called monomers.
• Polymers make up many materials in living organisms, including, for example, proteins, cellulose, and nucleic acids.
• In addition, they form the basis of minerals such as diamond, quartz and feldspar, as well as artificial materials, including concrete, glass, paper, plastic and rubbers.

The word "polymer" means an indefinite number of monomer units. When the amount of monomers is very large, the compound is sometimes referred to as high polymer. It is not limited to monomers with the same chemical composition or molecular weight and structure. Some naturally occurring high molecular weight organic compounds consist of one type of monomer.

However, most natural and synthetic polymers are formed from two or more different types of monomers; such polymers are known as copolymers.

Natural substances: what is their role in our lives?

Organic macromolecular organic compounds play a decisive role in people's lives, providing basic structural materials and participating in vital processes.

• For example, the solid parts of all plants are composed of polymers. These include cellulose, lignin and various resins.
• Cellulose is a polysaccharide, a polymer made up of sugar molecules.
• Lignin is formed from a complex three-dimensional network of polymers.
• Wood resins are polymers of a simple hydrocarbon, isoprene.
• Another familiar isoprene polymer is rubber.

Other important natural polymers include proteins, which are polymers of amino acids, and nucleic acids. They are a variety of nucleotides. These are complex molecules consisting of nitrogen-containing bases, sugars and phosphoric acid.

Nucleic acids carry genetic information in the cell. Starches, an important source of food energy derived from plants, are natural polymers composed of glucose.

Chemistry of macromolecular compounds releases inorganic polymers. They are also found in nature, including diamond and graphite. Both are made of carbon. Worth knowing:

• In diamond, carbon atoms are connected into a three-dimensional network, which gives the material hardness.
• In graphite, used as a lubricant and in pencil "leads", carbon atoms are bonded in planes that can slip through each other.

Many important polymers contain oxygen or nitrogen atoms, as well as carbon atoms in the main chain. Such macromolecular materials with oxygen atoms include polyacetals.

The simplest polyacetal is polyformaldehyde. It has a high melting point, is crystalline, resistant to abrasion and solvents. Acetal resins are more like metal than any other plastics, and are used in the manufacture of machine parts such as gears and bearings.

Substances obtained by artificial means

Synthetic macromolecular compounds are produced in various types of reactions:

1. Many simple hydrocarbons, such as ethylene and propylene, can be converted into polymers by adding one monomer after another to the growing chain.
2. Polyethylene, consisting of repeating ethylene monomers, is an additive polymer. It can have up to 10,000 monomers connected in long spiral chains. Polyethylene is crystalline, translucent and thermoplastic, that is, it softens when heated. It is used for coatings, packaging, molded parts, as well as for the manufacture of bottles and containers.
3. Polypropylene is also crystalline and thermoplastic, but harder than polyethylene. Its molecules can consist of 50,000-200,000 monomers.

This compound is used in the textile industry and for the manufacture of molded objects.

Other additive polymers include:

• polybutadiene;
• polyisoprene;
• polychloroprene.

All of them are important in the production of synthetic rubbers. Some polymers, such as polystyrene, are glassy and transparent at room temperature, as well as thermoplastic:

1. Polystyrene can be painted in any shade and is used in the manufacture of toys and other plastic items.
2. If one hydrogen atom in ethylene is replaced by a chlorine atom, vinyl chloride is formed.
3. It polymerizes into polyvinyl chloride (PVC), a colorless, hard, hard, thermoplastic material that can be made in many forms, including foams, films and fibers.
4. The vinyl acetate obtained by the reaction between ethylene and acetic acid polymerizes to amorphous, soft resins used as coatings and adhesives.
5. It copolymerizes with vinyl chloride to form a large family of thermoplastic materials.

A linear polymer characterized by the repetition of ester groups along the main chain is called a polyester. Open-chain polyesters are colorless, crystalline, thermoplastic materials. Those synthetic macromolecular compounds that have a high molecular weight (from 10,000 to 15,000 molecules) are used in the manufacture of films.

Rare synthetic polyamides

Polyamides include naturally occurring casein proteins found in milk and zein found in corn, which are used to make plastics, fibers, adhesives and coatings. It is worth noting:

• Synthetic polyamides include urea-formaldehyde resins, which are thermosetting. They are used for the manufacture of molded objects, as well as adhesives and coatings for textiles and paper.
• Polyamide resins known as nylon are also important. They are durable, resistant to heat and abrasion, non-toxic. They can be painted. The most famous direction in use is as textile fibers, but they have many other functions.

Another important family of synthetic high molecular weight chemical compounds consists of linear repetitions of the urethane group. Polyurethanes are used in the manufacture of elastomeric fibers known as spandex and in the manufacture of coating substrates.

Another class of polymers are mixed organic-inorganic compounds:

1. The most important representatives of this family of polymers are silicones. The composition of macromolecular compounds includes alternating silicon and oxygen atoms with organic groups attached to each of the silicon atoms.
2. Low molecular weight silicones are oils and lubricants.
3. Species with a higher molecular weight are versatile elastic materials that remain soft even at very low temperatures. They are also relatively stable at high temperatures.

The polymer may be three-dimensional, two-dimensional and single. Repeating units often consist of carbon and hydrogen, and sometimes of oxygen, nitrogen, sulfur, chlorine, fluorine, phosphorus, and silicon. To create a chain, many units are chemically bonded or polymerized together, in connection with which the characteristics of high molecular weight compounds change.

What features do high molecular weight substances have?

Most polymers produced are thermoplastic. After the polymer is formed, it can be heated and reformed again. This property makes it easy to handle. Another group of thermoset materials cannot be melted: once the polymers are formed, reheating will lead to decomposition, but not to melting.

Characteristics of high molecular weight polymer compounds using packaging as an example:

1. They can be very resistant to chemicals. Consider all cleaning fluids in your home that are packaged in plastic. Describes all the consequences of contact with eyes, but skin. This is a dangerous category of polymers that dissolves everything.
2. While solvents easily deform some plastics, other types of plastic are placed in non-breaking containers for aggressive solvents. They are not dangerous, but can only cause harm to humans.
3. Solutions of macromolecular compounds are most often supplied in simple plastic bags to reduce the percentage of their interaction with substances inside the container.

As a rule, polymers are very light in weight with a significant degree of strength. Consider a range of applications, from toys to the frame structure of space stations, or from thin nylon fiber in pantyhose to Kevlar, which is used in body armor. Some polymers float in water, others drown. Compared to the density of stone, concrete, steel, copper or aluminum, all plastics are lightweight materials.

The properties of macromolecular compounds are different:

1. Polymers can serve as thermal and electrical insulators: appliances, cords, electrical outlets and wiring that is made or coated with polymeric materials.
2. Thermal resistance of appliances in the kitchen with handles for pots and pans made of polymers, handles for coffee pots, styrofoam for refrigerators and freezers, insulated cups, coolers and utensils for the microwave.
3. The thermal underwear worn by many skiers is made of polypropylene, and the fiber in winter jackets is made of acrylic and polyester.

High molecular weight compounds are substances with an unlimited range of characteristics and colors. They have many properties that can be further improved by a wide range of additives to expand the application. Polymers can serve as the basis for imitating cotton, silk and wool, porcelain and marble, aluminum and zinc. In the food industry, they are used to give edible properties to fungi. For example, expensive blue cheese. It can be eaten without fear due to polymer processing.

Processing and application of polymer structures

Polymers can be processed in various ways:

• Extrusion allows the production of thin fibers or heavy massive tubes, films, food bottles.
• Injection molding makes it possible to create complex parts, for example, large parts of the car body.
• Plastics can be cast into barrels or mixed with solvents to become adhesives or paints.
• Elastomers and some plastics stretch, have flexibility.
• Some plastics expand during processing to maintain their shape, such as drinking water bottles.
• Other polymers can be foamed, for example, polystyrene, polyurethane and polyethylene.

The properties of macromolecular compounds vary depending on the mechanical effect and the method of preparation of the substance. This makes it possible to apply them in various industries. The main macromolecular compounds have a wider range of purposes than those that differ in special properties and production methods. Universal and "whimsical" "find themselves" in the food and construction sectors:

1. High molecular weight compounds are composed of oil, but not always.
2. Many polymers are derived from repeating units previously formed from natural gas, coal, or crude oil.
3. Some building materials are made from renewable materials such as polylactic acid (from corn or cellulose and cotton lint).

It is also interesting that they can hardly be replaced with anything:

• Polymers can be used to make items that do not have alternatives from other materials.
• They are turned into transparent waterproof films.
• PVC is used to make medical tubes and blood bags that extend the shelf life of the product and its derivatives.
• PVC safely delivers flammable oxygen to non-combustible flexible tubes.
• And antithrombogenic material, such as heparin, can be included in the category of flexible PVC catheters.

Many medical devices to ensure effective functioning are focused on the structural features of macromolecular compounds.

Solutions of macromolecular substances and their properties

Since the size of the dispersed phase is difficult to measure and colloids look like solutions, they sometimes identify and characterize physicochemical and transport properties.

A hydrocolloid is defined as a colloidal system in which particles of a molecule of high molecular weight compounds are hydrophilic polymers dispersed in water.

Other major hydrocolloids are xanthan gum, gum arabic, guar gum, locust bean gum, cellulose derivatives such as carboxymethyl cellulose, alginate and starch.

The interaction of macromolecular substances with other particles

The following forces play an important role in the interaction of colloidal particles:

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High-molecular compounds even include crystals that fall into the category of colloidal substances. This is a highly ordered array of particles that forms at a very large distance (usually of the order of several millimeters to one centimeter) and looks similar to their atomic or molecular counterparts.

These spherical particles are deposited in highly siliceous reservoirs. They form highly ordered arrays after years of sedimentation and compression under the influence of hydrostatic and gravitational forces. Periodic arrays of spherical particles of the sub-micrometer range provide similar arrays of interstitial voids that act as a natural diffraction grating for visible light waves, especially when the distance between interstitials is of the same order of magnitude as the incident light wave.

Thus, it was found that due to repulsive Coulomb interactions, electrically charged macromolecules in an aqueous medium can exhibit long-range crystal-like correlations with distances between particles, often significantly exceeding the diameter of individual particles.

In all these cases, the crystals of the natural high-molecular compound have the same brilliant iris (or play of colors), which can be attributed to the diffraction and constructive interference of visible light waves. They satisfy Bragg's law.

A large number of experiments to study the so-called "colloidal crystals" arose as a result of relatively simple methods developed over the past 20 years to produce synthetic monodisperse colloids (both polymer and mineral). Through various mechanisms, the formation of long-range order is realized and maintained.

Molecular weight determination

Molecular mass is a critical property of a chemical, especially for polymers. Depending on the sample material, various methods are selected:

1. The molecular weight as well as the molecular structure of the molecules can be determined using mass spectrometry. Using the direct infusion method, samples can be injected directly into the detector to confirm the value of the known material or to provide the structural characterization of the unknown.
2. Information on the molecular weight of the polymers can be determined using a method such as size and size exclusion chromatography.
3. To determine the molecular weight of polymers, it is necessary to understand the solubility of this polymer.

The total mass of the compound is equal to the sum of the individual atomic masses of each atom in the molecule. The procedure is carried out according to the formula:

1. Determine the molecular formula of the molecule.
2. Use the periodic table to reveal the atomic mass of each element in the molecule.
3. Multiply the atomic mass of each element by the number of atoms of that element in the molecule.
4. The resulting number is represented by a subscript next to the symbol of the element in the molecular formula.
5. Combine all the values ​​together for each individual atom in the molecule.

An example of a simple calculation of low molecular weight: to find the molecular weight of NH ₃ , the first step is to search for the atomic masses of nitrogen (N) and hydrogen (H). So, H = 1.00794N = 14.0067.

Then multiply the atomic mass of each atom by the number of atoms in the compound. There is one nitrogen atom (no subscript is given for one atom). There are three hydrogen atoms, as indicated in the subscript. So:

• Molecular mass of the substance = (1 x 14.0067) + (3 x 1.00794)
• Molecular weights = 14.0067 + 3.02382
• Result = 17,0305

An example of calculating the complex molecular weight of Ca ₃ (PO ₄ ) ₂ is a more complex calculation option:

From the periodic table, the atomic masses of each element:

• Ca = 40.078.
• P = 30.973761.
• O = 15.9994.

The hard part is figuring out how much of each atom is present in the compound. There are three calcium atoms, two phosphorus atoms and eight oxygen atoms. If part of the connection is in brackets, multiply the subscript immediately following the element symbol by the subscript that closes the brackets. So:

• The molecular weight of the substance = (40.078 x 3) + (30.97361 x 2) + (15.9994 x 8).
• Molecular mass after counting = 120.234 + 61.94722 + 127.9952.
• Result = 310.18.

By analogy, complex forms of elements are calculated. Some of them consist of hundreds of values, therefore, now automated machines are used with a database of all g / mol values.