Polymers in your life

 

Polymers are a large part of our daily lives and without them around, this world would be very, very different, if not impossible to live in. However, most people do not even know what a polymer is, or just how widespread they are around us.  Many a times, the term polymer is taken to refer to plastics, but it actually encompasses a larger class of natural and synthetic materials with a wide range of properties. A variety of polymers exist in nature. Among these are silk, cotton, cellulose, shellac, amber, as well as the incredibly complex polymers like RNA (ribonucleic acid) and DNA (deoxyribonucleic acid), which hold our genetic codes. The list of synthetic polymers includes polyethylene, synthetic rubber, Bakelite, neoprene, nylon, PVC, polystyrene, teflon, polypropylene, polyacrylonitrile, silicone, and many more.

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So, what exactly is a polymer? Poly means “many” and mer means “part” or “segment”. A polymer is a large molecule made up of many many unit molecules (or monomers) strung together to form long chains. A simple example is polyethylene (a.k.a. polythene), whose repeating unit is based on ethylene (C2H4) monomer. Now, how long are these chains? Well, a single polymer molecule chain can be comprised of hundreds and thousands (or even millions!) of monomers. And there are billions of such chains in objects made of polymers. The properties of anything made out of polymers, i.e., how they look, feel and act depend on what kind of molecules they’re made up of and how they are connected and put together. The long polymer chains can get tangled up randomly amongst themselves like a bowl of spaghetti, or they can remain stiff and line up next to each other. As a result, some polymer materials are rubbery, like a bouncy ball, some are sticky and gooey, while some others are hard and tough, like a skateboard.

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Although the initial examples of modern polymer science can be found in the 19th century, the very first known polymer scientists were actually the pre-hispanic Mesoamericans (the Aztecs, Olmecs and Mayans) who lived in the region that is now Mexico and parts of Central America. Recent research by MIT scientists has revealed that the Mesoamericans not only figured out how to produce rubber from the sap of the native Castilla elastica tree more than 3000 years ago, but they could even cleverly engineer a variety of different polymers by combining different proportions of this sap and juice from the morning glory species called Ipomoea alba. A 50-50 blend of the latex (produced by drying the sap) and morning glory produced maximum bounciness, perfect for the rubber balls. Pure latex worked best for rubber bands and adhesives, while a three-to-one mix of latex to morning glory provided the most durable material, perfect for sandals. By the time the Spanish arrived in the 16th century, Mexico had a huge rubber industry, producing 16,000 rubber balls a year as well as a wide variety of other products. The balls were used as offerings in religious rituals or in ceremonial games played on stone courts like handball.

The first modern example of polymer science is Henri Branconnot’s work with cellulose in the 1830s. Soon after, two inventors, Friedrich Ludersdorf of Germany and Nathaniel Hayward of the US, independently discovered that adding sulfur to raw rubber helped prevent the material from becoming sticky. In 1839, the American inventor, Charles Goodyear, was experimenting with the sulfur treatment of natural rubber and developed a process known as “vulcanization” that involved cooking the rubber with sulfur. The sulfur in this process causes the polymer chains of the latex to become cross-linked, making them stronger, more durable and more elastic. The morning glory juice used by the ancient Mesoamericans has sulfur-containing amino acids that apparently do much the same thing, although the density of cross-links is much greater in the vulcanized rubber. Vulcanized rubber represents the first commercially successful product of polymer research. In 1907, Leo Baekeland invented the first synthetic polymer called Bakelite, followed by rayon, which was developed in 1911.

Despite significant advances in polymer synthesis, the molecular nature of polymers was not understood until the 1920s.  When Hermann Staudinger, a German scientist, proposed that polymers were large molecules comprised of long chains of atoms held together by covalent bonds, he was ridiculed by many other scientists. The common wisdom was that the structures of such materials as rubber and Bakelite were actually many small molecules which were held together by an unknown force. It took over a decade for Staudinger’s work to gain wide acceptance in the scientific community, work for which he was awarded the Nobel Prize in 1953.

It was not until World War II that significant changes took place in the polymer world. Once the world went to war, our natural sources of wool, silk, latex and other materials were cut off, making the development and use of synthetic polymers like nylon, polyethylene, acrylic, neoprene etc. critical. In the intervening years, the development of advanced polymers such as Kevlar and Teflon have continued to fuel a strong polymer industry that has evolved into one of the fastest growing industries in the world today.

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