What Is a Monomer?
Polymers are large molecules that consist of long chains of repeating structures, called monomers. The word monomer comes from the Greek, mono meaning one and meros meaning part; thus a monomer is one part of a long chain that makes up a polymer (meaning many parts). Monomers bond together to form polymers during a chemical reaction called polymerization, where the two molecules link together by sharing electrons in what is called a covalent bond.
A key feature of a monomer is its ability to bond with at least two other molecules. The number of molecules a monomer is able to bond with is determined by the number of active sites where the covalent bonds can be formed. If a monomer can only bond with two other molecules, chain-like structures are formed. If a monomer can bond with three or more other monomers, more advanced, three dimensional, cross-linked polymers can be built. Carbon is often a major part of most polymers as it is one of the few elements that can bond in four different directions with four other atoms.
A polymer can consist of the same monomer being repeated, called a single-monomer formed polymer, or it can consist of more than one type of monomer, called a co-polymer. Within a co-polymer, monomers can be arranged in a number of different ways:
- Alternating co-polymers — monomers alternate in a regular pattern (e.g. ABAB);
- Periodic co-polymers — monomers are arranged into a repeating sequence (e.g. ABBAABBA);
- Random co-polymers — monomers occur in a random sequence with no discernable pattern;
- Statistical co-polymers — monomers are arranged according to a statistical rule;
- Block co-polymers — two or more single-monomer formed polymers that are linked together by covalent bonds (e.g. AAAAABBBBB).
The physical arrangement of the monomers that make up the polymer backbone dictates the structural properties of that polymer. Structure has a strong effect on other properties of the polymer, including solubility in water and durability. For instance, two polymers can contain the same monomer molecules, but due to the arrangement, they can have entirely different properties.
Monomers and polymers occur both naturally and as man-made substances. The most common natural monomer is glucose, which can bond into very large carbohydrates, including cellulose and starch. Amino acids, which make proteins, and nucleotides, which form DNA and RNA, are two other examples of naturally occurring organic monomers.
There are also many synthetic examples of monomers and polymers. Hydrocarbons, such as phenylethene and ethane, are monomers that are used to make plastics, including polystyrene, which is one of the most widely used plastics. Other common synthetic monomers include acrylic acid and acrylamide.
Written by Victoria Blackburn
