Difference Between Polymer And Monomer
What Is a Polymer?
A polymer is composed of giant molecules known as macromolecules. They are formed by the combination of from hundreds to tens of thousands of smaller molecules. A polymer forms when large numbers of small molecules, known as monomers, become chemically bound.
Many biochemical and biological functions are performed by natural polymers. Protein is a polymer of amino acids, and cellulose is a polymer of sugar molecules. Silk, wool, and cotton are natural polymers as is natural rubber. Fibers such as rayon and cellulose acetate are made by chemical modification of natural cellulose.
Think of a paper clip as a single monomer molecule. Joining paper clips together in a chain represents polymerization—the chemical process in which a polymer is formed. A paper clip chain thousands of paper clips long represents a single polymer molecule. We might call this a poly (paper clip) molecule and represent it as paper clipn, where n indicates the number of paper clip “molecules.” The number n is usually a very large number.
The monomer for polyethylene is ethylene (CH2 = CH2), which, like the raw materials for many polymers, is composed of carbon and hydrogen. Ethylene undergoes addition polymerization, one of the two major routes to polymer formation:
…+CH2 = CH2 + CH2 = CH2 + CH2 = CH2 → (CH2CH2)n
The product of this addition polymerization, represented at the right of the arrow, is called polyethylene. Ethylene molecules add one by one at the end of the growing chain and the polymer has the same relative composition as the monomer. Polyethylene is a synthetic organic polymer—synthetic because it is man-made and organic because it is composed mainly of carbon combined with atoms of other elements.
Polyethylene is a typical thermoplastic. As the temperature is raised, its individual chains move around more freely and the material softens. A thermoset plastic, by contrast, once it has cured, remains rigid when heated because the chains are held in place by cross-links—groups firmly bound to different chains at each end. The cross-links are formed during curing, after the material has been molded into the desired shape.
Many polymers, unlike polyethylene, are composed of more than one type of monomer. Nylon (the common name for thermoplastics known as polyamides), for example, is a co-polymer—it is made from two monomers. Nylon is formed by a process called condensation polymerization, the second major type of polymerization. During condensation, each monomer loses a few atoms that form a small molecule, often water.
Monomers can combine in a variety of different patterns that also influence properties. Spandex is a block copolymer and is representative of a class of polymers known as thermoplastic elastomers. Combining alternating segments of a rubberlike polymer and a rigid thermoplastic combines the elasticity of a conventional rubber with the ease of processing of a thermoplastic. Spandex is the name of the fiber form of the family of thermoplastic elastomers known as polyurethanes.