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Polymer is a Greek word meaning ‘many parts’. Literally, polymers are substances with many repeating units. This paper will briefly discuss polymers and polymerization as used in chemistry.
Definition of a Polymer
A polymer is defined as a large molecule that is made up of several structural units connected by chemical bonds. They are in fact long chains of organic molecules that are formed from smaller units called monomers. Polymers consist of several repeating monomers that form long chains. Polymers can be linear, branched or highly branched developing into a 3-dimensional structure.
Types of Polymers
Polymers can be either naturally occurring or synthetic. Some of the naturally occurring polymers include proteins, cellulose, starch, and latex. Synthetic polymers are those ones that are manufactured by humans for wide use. Examples of synthetic polymers include plastics used in everyday life like wrapping, packing, building materials, textiles, automobiles, television sets, CDs and many other products.
Formation of Polymers
Polymers are formed through a process called polymerization. Polymerization involves combining the small molecules (monomers). There occurs a chemical reaction where a large number of monomers are joined in a sequential manner to form a large chain. In many cases, only one monomer is used to form a polymer, although sometimes more than one type of monomers can be used. We have seen that the repeat monomer in the polymer corresponds to the monomer but there are exceptions to this: poly(vinyl alcohol) which is considered to be made from a monomer called vinyl alcohol (CH2CHOH). In essence though, there is a monomer called vinyl alcohol. The polymer poly(vinyl ethanoate) is made from vinyl ethanoate; and then the product is hydrolyzed to form the desired polymer. The size of a polymer is usually defined by the number of its repeat units or by its mass (Flory, 1953).
Many of the polymers used commercially are organic in nature. This means that they are based on carbon compounds (including silicones). Other elements involved in polymer chemistry include oxygen, nitrogen, fluorine, chlorine, sulfur, and other compounds able to form covalent bonds with carbon.
Classification of Polymers
There are different ways of classifying polymers. One of them is to use their response to thermal treatment and thus polymers are divided into thermosets and thermoplastics. Thermosets are those polymers that do not melt when heated and will only decompose at very high temperatures. Thermoplastics are those polymers that melt when they are heated and become solids again when they are cooled. Thermoplastics usually contain linear or slightly branched molecules while thermosets are essentially cross-linked molecules hence they consist of a 3-dimensional structure (Flory, 1953).
Another type of classification is the one based on the type of chemical reactions involved during polymerization. There are two of these, namely condensation and addition polymers. Condensation polymers are those formed by a small loss of molecules e.g. water (H2O). An example is also the formation of polyester. On the other hand, addition polymers are those formed by additional reaction involving an unsaturated monomer. An example here is the reaction that takes place during polymerization of vinyl chloride (Flory, 1953).
Polyethylene is one of the simplest polymers. It is composed of repeating chains of –CH2- units. The polymer is produced by polymerization of ethylene whose structural formula is CH2=CH2. This polymer has different properties depending on how it was polymerized. Polyethylene is used in the manufacturing of milk bottles, jugs, plastics films, and sandwich bags. Other common polymers include polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, and polyurethane (Shakhashiri).
The Importance of Polymers
Natural polymers are very important. For example, cellulose allows plants to grow towards the sun by providing the much needed stiffness, starch is efficient in storing energy while proteins (enzymes in particular) are used in catalyzing biological reactions in the body. Other polymers like DNA and RNA are accountable for storing genetic information in us. Natural polymers are thus very important in our lives as well as that of the plants.
Synthetic polymers are used almost in every aspect of our daily lives. This is because they are easily replaced. Most synthetic polymers are organic and thus their quantities are low when compared to those of ceramics or metals. Plastics come in different properties, chemical resistance, cost, and can be molded to desired shapes. Packing industries use plastics instead of aluminum, glass, and paper for several reasons. It is cheaper to package into plastics, and they have a lower mass and appeal to many people (Teegarden, 2004).
The other reason why synthetic polymers are popular is because of its unique properties. Governments and NGOs have funded researches into the synthesis of polymers that has seen production of a wide variety of synthetic polymers with properties that cannot be found in other materials. Polymers are now widely used in the improvement of new technologies, like optic fibers, automobile tires, space travel, production of artificial organs, water-based paints, and production of computers and integrated circuits. It is also possible to produce polymers that are semiconductors, insulators or magnetic polymers. Some polymers are able to change their color or switch from being transparent to opaque when exposed to electrical fields or certain temperatures (Teegarden, 2004).
Polymers are large molecules made from several monomers, and they may be linear or branched. Monomers are the building blocks for polymers. Polymers, either natural or synthetic, play a vital role in our lives. Natural polymers support life while synthetic polymers are used to support life in various ways due to their organic nature.