Polymers and Elastomers The word 'polymer' means 'many parts'. A polymer molecule is a long chain of covalent-bonded atoms, such as the one shown on the right. Most polymers are carbon based, with a large molecular weight, and have relatively low melting points. Natural rubber, for example, is a polymer, and has a molecular weight of about 350,000. Two important polymeric materials are plastics and elastomers (rubbers). There are many types of each. Polymers have many varied properties, which allow for their extensive use in society. Uses include car parts, food storage, electronic packaging, optical components, protective coverings, and adhesives. Silly Putty is a polymer. There are two types: - Plastics are a large group of synthetic polymers containing many polymer molecules locked into place. There are many types of plastics, such as polyethylene and nylon. Plastics can be divided into two classes, thermoplastics and thermosetting plastics, depending on how they are structurally and chemically bonded. - Elastomers, or rubbers, allow movement of individual polymer molecules. These materials can be stretched a large amount when a force is applied to them, and can return to their original shape (or almost) when the force is released. Electron microscope image of the polymer molecules in a styrofoam packaging 'peanut'. In both types of polymers, secondary bonds hold groups of these polymer chain molecules together to form a polymeric material, much like a handful of cooked spaghetti noodles. If the molecules are well-attached to each other, you get a plastic. But if the molecules aren't stuck to each other too much, the material can be stretched, and is called an elastomer. Elmer's Glue is a liquid polymer, where the molecule strands are not joined at all ... they can slide past each other, and the liquid can 'flow'. When the borax is added, it forms chemical bonds between the strands, linking them together, and stopping the material from flowing. It is now a rubbery solid. But the molecules aren't fixed in place, like a hard plastic, so they can still be stretched. The putty is a form of elastomer, even though it doesn't snap back to its original shape after you stretch it. On the left, a single elastomer molecule is in its unstretched (rest) state. Work must be performed to elongate the chains, (below), and when the force is removed, the chains may return to their disordered 'spaghetti-like' state. Silly Putty | Main Page