Category Polymers

Why does a rubber band regain its original shape after it is stretched?

          You might have tried stretching a rubber band or squeezed a rubber toy. Have you noticed that they regain their original shape once they are released? This is possible because they are elastomers.

          Elastomers are rubber-like solid polymers with elastic properties. That is, they can be easily stretched and can regain their original shape no matter how much you squeeze or stretch them. The force of attraction between the molecules of an elastomer is weak. Remember vulcanized rubber that we discussed earlier? That too is an elastomer. Vulcanized rubber has a cross linked chain which is helps it remain its original form.

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How is an addition polymer different from a condensation polymer?

          Addition polymers are formed by the repeated addition of monomers. No by-products are formed in this linkage.

          Polyethene which is used for making plastic carry bags and toys are formed by the process of addition. The monomers either contain a double bond or have a ring structure containing three to seven atoms.

          On the other hand, condensation polymers are formed when monomers condense while bonding. By-products are formed in this reaction and small molecules like water are lost. Most of the natural polymers are synthesized using this process.

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How are polymers classified based on their structure?

          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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How can we classify polymers?

          We have a tendency to classify everything around us. Similar things are often grouped together for the ease of understanding. Polymers too can be grouped based on different criteria.

          We already discussed natural, synthetic and semi-synthetic polymers. This classification is based on their source. Are there other possible ways to classify them? Indeed yes!

         Polymers can be clubbed together based on their structure, molecular forces and type of polymerization. Look at the diagram to get a clear picture of this.

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Why is the World War II era a significant period in the history of polymers?

          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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Who is known as the father of polymer chemistry?

          On account of his contributions to polymer science education and research, Herman Francis Mark is known as the father of polymer chemistry. He worked on polymers for almost 75 years and produced more than 600 research papers and 40 books about polymer chemistry. A huge number indeed!

          Mark studied molecular structures of natural textile fibres like silk and wool. He applied modern physics to the study of large molecules; his work on molecular structures using X-Ray diffraction provided sufficient evidence for macromolecular theory of polymer structure.

         Mark’s interests included the mechanical properties of polymers. He led the commercial production of polystyrene, a tough colourless plastic. He is also credited for developing several theories and even an equation!

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