What is a polymer? Polymers are macromolecules made up of repeating units of the same kinds or different kinds. “Poly” means many and “meres” means parts. The most familiar polymer at our home is nothing but our staple food made up of starch.
By photosynthesis, the carbon dioxide (addition of hydrogen) is reduced to glucose by plants. Many glucose molecules formed within the leaves link together by a bond called glycosidic bond to form a complex molecule of starch. The starch is stored in different parts of the plant body. For example, Rice, Wheat, Barley, Tapioca, Sweet potato, etc., all contain starch. We consume cooked starch. Cooked starch is also polymer. As it is a macromolecule, we cannot absorb starch as it is. The bond between the glucose unit needs to break to release glucose. This is done in our body by using an enzyme, that is present in saliva (salivary amylase) and in our intestine (intestinal amylase). Finally, glucose molecules are released as an end product and are absorbed into the bloodstream for further metabolism to release energy.
Another natural polymer is cellulose. The plant cell wall is made up of cellulose. It is also made up of glucose units linked together by another type of bond known as the beta-1,4-glycosidic bond. But in our body, no enzymes are available to break the bond. Little amount of digestion is possible by bacteria living in our gut of the human body, so the bulk amount of cellulose remains undigested and forms the roughage.
Rubber is familiar to everyone. It is also a natural polymer produced within the bark of Hevea brasiliansis. But the monomeric unit is not glucose, it is made up of repeating units of a molecule known as Isoprene.
Protein is the next polymer very essential for our body. All enzymes are made up of proteins without enzymes no chemical reactions take place. Proteins are polymers of amino acids. As it is a macromolecule, we cannot absorb the protein as such. It needs to be digested. This is done in the stomach and small intestine by specific proteolytic enzymes, finally by digestion free amino acids are formed which are absorbed into the bloodstream to produce specific proteins by a chemical reaction inside the body. Nail, hair, actin, myosin, etc., are examples.
Other examples of natural proteins include silk, wool, DNA, RNA, collagen, chitin, etc.,
In the modern world, we use synthetic man-made polymers through chemical reactions. For example, plastic, fibre, computer parts, and other electrical body parts are all made up of synthetic fibres. Raw polymers are subjected to heat, UV, or other chemicals that result in close linking of monomeric units and are modified to heat-resistant lightweight polymer products. For example, liquid polymer is the raw material for making rubber stamps. This liquid is sensitive to UV rays which result in cross-linking of monomeric units and result in the formation of hardened letters and graphics. Recycling of plastic bottles is also possible to form special plastic products commonly known as rPET (Recycled Polyethylene Terephthalate).