My Science School

          Properties of a polymer depend on how monomers are linked together. There are three basic structures for polymers – linear, branched and cross-linked.

          Linear polymer is the simplest polymer. It has a long, straight chain with identical linkage. PVC is a liner polymer. Teflon is another linear polymer made from tetrafluoroethylene. Branched chain polymers have a long, straight chain with branches of different lengths originating at random points. These branches are known as side chains and can have different lengths. Low-density polyethene (LDPE) used in plastic bags is a branched chain polymer.

          There is another category known as cross-linked polymers. It has a three dimensional network of monomers with long chains of linear or branched polymers.

          A cross linked polymer has strong covalent bonding that attracts other polymer chains and creates a more stable material. It is also known as network polymer. Bakelite which is used to make sockets is a network polymer.

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          Polymer production emerged as a strong commercial industry during the Second World War. There was a scar-city of natural materials like rubber and silk during the war years, which created a high demand for them.

          The increasing demand created a crisis which further led to an increase in the production of synthetic substances like nylon and synthetic rubber. Moreover, the scarce natural resources needed to be preserved. This made the synthetic alternatives a priority and plastics made it possible!

          The increase in the production of synthetic polymers touched almost all aspects of daily life. Nylon was used for making parachutes, body armours, ropes and helmet liners. It caused a huge change in the fashion industry as well. Rayon, the new synthetic material discovered in the 1930s solved the crisis in natural fabrics and was widely used to make clothing.

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          Herman Staudinger was not the first chemist to work with polymers. But his significant contributions laid the foundations to diverse applications of polymers.

          Staudinger was a professor in organic chemistry at Zurich when he proposed some of the pioneering theories on polymer structures of fibres and plastics.

          In the 1920s, he found out that rubber has a high molecular weight. He also presented a paper showing several reactions capable of forming structures high molecular weight.

          Staudinger explained how smaller units combine to form a large structure. He called the process polymerization. Before that, polymers were thought of as aggregates of molecules and this idea was based on Thomas Graham’s work. His studies on biological macro-molecules led to a lot of later discoveries of commercial importance.

          Staudinger’s ideas were criticized heavily by other chemists of his time, but were finally accepted by the 1950s. In 1953, he was awarded the Nobel Prize in chemistry for his contributions in understanding macromolecular chemistry.

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          Have you observed PVC pipes that are attached to the water tank? You might have noticed that the pipes exposed to sunlight lose colour after a while. These pipes will also lose their strength and become brittle. PVC pipes lose hydrogen chloride gas when exposed to high temperatures.

          Polymers undergo a change their properties like colour, shape or molecular weight when they are exposed to one or more environmental factors like heat, light or chemicals. This change is known as polymer degradation. It is usually undesirable. However, it is useful in recycling polymer waste. Biodegradable plastics are degraded with the help of microorganisms.

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            We have been talking about polymers a lot. But how are they synthesized? A polymer is made by combining monomers to form a long chain and for this; monomers react and combine in a process called polymerization.

            A monomer has the capacity to form chemical bonds with at least two other monomer molecules. Nucleic acid is a natural polymer which is formed when nucleotide monomers bond. How does a PVC pipe take shape? Vinyl chloride is the monomer that reacts in a certain fashion to form polyvinyl chloride (PVC).

            Polymers are formed either by repeated addition or condensation of monomers. Accordingly, polymerization is generally of two types which we will talk about later in detail.

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          Natural polymers can be modified by chemical treatment.

          The product obtained after the modification is known as a semi-synthetic polymer. A new polymer is synthesized out of a naturally occurring one and hence the name!

          Vulcanized rubber is a semi-synthetic polymer. Rubber in its natural form is not thermally stable. It becomes very hard when it is cold and melts down in heat. But, when treated with sulphur, rubber achieves thermal stability and becomes flexible and can be used to make a range of useful products. This chemical treatment of rubber is known as vulcanization.

           Similarly, many other natural polymers can be modified into semi-synthetic polymers with desirable properties.

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          The very term polymer suggests that it is basically a man-made product. But, are there natural polymers? Did polymers exist in nature before humans learned to make them?

          Some polymers are found in plants and animals and they are known as natural polymers. The human body is an amazing system made of several polymers; the proteins and nucleic acids found in our body are actually polymers. The starch present in our body is made of polysaccharide, yet another polymer. Even our RNA and DNA are polymer structures.

           Plants are made up of a polymer called cellulose. Latex, a sticky white substance obtained from various plants is another commercially important natural polymer. It is harvested and made into rubber. Silk and wool are also natural polymers.

          Natural polymers are often formed by condensation reaction. The monomers condense to form polymers and in this process, they lose smaller molecules. Water is obtained as a by-product when the monomers of a natural polymer combine.

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          Polymer is a Greek word. Poly means many and mer means units. The Greek word thus translates to ‘many units’.

         The smaller parts are known as monomers. The word was coined in 1840 by Jons Jacob Berzelius. He was a chemist, but most of his works do not actually concern polymers.

         The repeating chains may be simple at times, say a string of five or six atoms. Monomers can also form complex structures like a ring. The repeating units of polymers are often made of hydrocarbons. Sometimes, other elements like oxygen, nitrogen, sulphur, chlorine, fluorine and phosphorous are also used.

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          You might have made paper garlands in school. How do you make them? You hook a piece of paper to another and repeat the process till you get a large chain of papers, forming a garland. Think of polymers in the same way.

           A polymer is a giant molecule which is made by a chain of smaller units and these sub units are known as mers. You know what a molecule is. It is the smallest particle which retains the chemical features of a compound. Each unit is linked to the other by a chemical bond. There is a wide range of polymers around us, from the proteins present in our body to thermoplastics that have a variety of uses. A polymer varies from another based on the qualities it possesses and the process of its formation.