Organic Chemistry

Polymers

            The Mayans of Central America were one of the first to use natural latex polymers from the rubber tree to produce elastic, bouncing balls. Archeologists believe that the neighboring Aztecs used rubber balls in ceremonial games. The Native Americans gathered the milky exudates from cuts they made in a variety of trees. As it dried, they fashioned it into balls, footwear, and even bottles. In 1736 French explorers collected some of the condensed juice of the Hevea tree and sent it to Europe where it was analyzed by Joseph Priestly and other scientists. Priestly noted that the gum could “rub” pencil marks off paper, and thus the term “rubber” was coined. Although most 18th century scientists initially thought that rubber was just an interesting curiosity, its many valuable properties were later discovered. Eventually, inventors incorporated it in a wide variety of materials including tires, waterproofing, and sporting goods.

            Rubber is one of many naturally occurring polymers – large molecules that consist of up to millions of repeated monomer units. The term “polymer” is derived from the Greek words “polys” meaning many and “meros” meaning parts. The most abundant organic molecules in the world are polymers. Cellulose and lignin (the main fibers in wood), starch (a natural storage form of sugar in plants), collagen (the fiber that holds soft tissues together in our bodies), DNA, RNA and proteins (key informational and structural molecules), and even cotton, wool, silk and flax (natural fibers used in clothing) are polymeric.

            Many polymers like starch and cellulose are homopolymers, chains consisting of only one repeating sub-unit or monomer. Others, like DNA and proteins, are known as copolymers because they contain two or more different monomers. Some polymers are linear, while others are branched or cross-linked. Cellophane tape is an example of a product made of linear polymers, most of which lie parallel to each other the way strands of spaghetti lie in a pack. Just as it is easier to separate the pieces of spaghetti into two bunches lengthwise, so it is easier to tear cellophane tape lengthwise (between chains) rather than crosswise (across chains).

            As more and more of the chemical properties of polymers were discovered, chemists produced a great variety of man-made polymers. Today polymers are an integral part of life in industrialized countries. They are widely used as adhesives, coatings, textiles, packaging, foams, electronic components, and structural composites. Many of these polymers are created to be durable and to last for a long time, and thus polymer recycling has become a significant concern.

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