Polymers are large molecules composed of smaller molecules called monomers. Monomers are produced and either grow together or are assembled to produce a single polymer. There are synthetic and natural polymers. Some examples of natural polymers would be wood, starches, fingernails, and hair. Synthetic polymers are usually referred to as plastics. Petroleum, is the primary monomer used to produce polymers. An English chemist named Alexander Parkes was the first scientist to produce the first synthetic polymer in 1862. John Wesley Hyatt, an American, was the first person to produce a useable polymer two years later. He named the product celluloid.
The prime virtue of polymers is a high strength-to-weight ratio. Industrial-strength polymers surpass titanium in tensile strength. To add strength and improve flexibility, polymers are sometimes fortified with short-fiber additives, mostly fiberglass. This is known as a polymer composite. One particular polymer has three times the strength of tempered steel and is being used in bullet proof vests. Another composite will be used to fasten together the sections proposed space stations. Polymers have also been used in cars, including the Chevrolet Camaro and the Pontiac Fiero.
New polymers are being created with more strength and flexibility
by combing two chemically different polymers and producing a
block copolymer. Combinations of block copolymers and composites
and intended for use in booster rockets and in materials of
Most common polymers are usually solid, but a new class of polymers is being introduced in a liquid crystal state. Although these polymers still have the physical characteristics of liquid, they are structured more like solids. Many liquid crystals are transparent at one temperature and colored at another temperature. This makes them suitable for use in liquid crystal displays, such as in digital watches, hand-held calculators, and lap-top computers. A new liquid polymer, consisting of a mixture of iron and nickel, is being used to make metal links that can be used in paper, glass, and on electronic circuit boards.
Despite the development and widespread use of polymers, scientific understanding is still sketchy. Polymer development has occurred through trial and error. Scientific shortcomings are becoming more apparent in the search for polymers that can meet the demands for high technology of today. The new study is on the microstructure of polymers while still in a liquid state. The purpose is to learn how the solid-state structure is developed. The ultimate goal is to be able to predict properties from a specific material under a constant set of processing conditions.
Poly(styrene-butadiene-styrene), or SBS, is a hard rubber, which is used for things like the soles of shoes, tire treads, and other places where durability is important. It is a type of copolymer called a block copolymer. Its backbone chain is made up of three segments. The first is a long chain of polystyrene, the middle a long chain of polybutadiene, and the last segment is another long section of polystyrene. Here's a picture:
Polystyrene is a tough hard plastic, and this gives SBS its durability. Polybutadiene is a rubbery material, and this gives SBS its rubber-like properties. In addition, the polystyrene chains tend to clump together. When one styrene group of one SBS molecule joins one clump, and the other polystyrene chain of the same SBS molecule joins another clump, the different clumps become tied together with rubbery polybutadiene chains. This gives the material the ability to retain its shape after being stretched.
SBS is made with some really clever chemistry using what is called living anionic polymerization. Click here to see just how SBS is made.
SBS is also a type of unusual material called a thermoplastic elastomer. These are materials which behave like elastomeric rubbers at room temperature but when heated can be processed like plastics. Most types of rubber are difficult to process because they are crosslinked. But SBS and other thermoplastic elastomers manage to be rubbery without being crosslinked, making them easy to process into nifty useful shapes.