Category Polymers

                    Think of the human body. What is it that gives us our shape? The skeleton of course. Without the skeleton, we would be a lump of flesh. Similarly all polymers have a skeleton which gives them their structure. Organic polymers have a carbon backbone. Their monomers are simple organic compounds.

           On the other hand, the backbone of an inorganic polymer is constituted by elements other than carbon, say phosphorous or sulphur. Most of the organic polymers have simple structures while inorganic polymers are highly branched with complex structures.

           Though they have carbon bonding, graphite and diamond are inorganic polymers. This is because they are constituted by carbon atoms alone which crosslink to give their structure.

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           Nylon is a synthetic fibre which is commonly used in the textile industry. The word fibre will give you an image of interlinked threads. Synthetic fibres are man-made fibres that are derived from several chemical processes. They can be easily woven because of their thread-like nature. The force of attraction between the monomers of a fibre is very strong; the monomers crosslink to form a strong hydrogen bond.

          Nylon is also used for making fishing nets, ropes and parachutes because it is strong and long lasting. Like nylon, polyester and rayon too are synthetic fibres. They are non-toxic substances and can be dyed.

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          Unlike thermoplastics, thermosetting plastics cannot be remoulded or reshaped. It assumes a permanent hard shape once heated.

          Initially, this is a liquid or a soft solid. Chemical reactions take place when it is heated and the long polymer chains crosslink to form a three dimensional structure. You might have bright coloured melamine dinnerware at home.  Melamine is a thermosetting plastic. Bakelite, which is used for insulating electric wires, also belongs to this category.

          Thermoplastics can be remelted quickly, but thermosetting plastics can withstand high temperatures. It cannot be recycled for the same reason.

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           Do you know how a plastic bottle is made? At first, the raw material used for making the bottle is heated and blown. It is then passed through another mould which gives it shape.

          The production of a plastic bottle is possible because the raw material can be moulded into any shape at a certain temperature. It then solidifies after cooling. Polymers of this kind are known as thermoplastics. Thermoplastics soften up on heating and harden when they are allowed to cool down They can be melted and recast into any possible shape. PET bottles and toys are has usually made of thermoplastics.

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          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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          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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