Polymers are large molecules made by joining many smaller molecules called monomers into long chains or networks. They matter because plastics, rubber, fibers, adhesives, proteins, and DNA all depend on polymer structure. A small change in the monomer or in how chains connect can greatly change strength, flexibility, melting behavior, and chemical resistance.
Understanding polymers helps explain both useful materials and environmental problems such as plastic waste.
Key Facts
- A polymer is a macromolecule made of many repeating units linked by covalent bonds.
- Monomer + monomer + monomer + ... -> polymer chain
- In addition polymerization, unsaturated monomers add together without forming a small byproduct.
- Ethene forms polyethylene: n CH2=CH2 -> [-CH2-CH2-]n
- In condensation polymerization, monomers join while releasing a small molecule such as H2O or HCl.
- Degree of polymerization: DP = number of repeat units in one polymer chain.
Vocabulary
- Monomer
- A monomer is a small molecule that can chemically bond to other similar or compatible molecules to form a polymer.
- Polymer
- A polymer is a large molecule made from many repeating units connected in a chain or network.
- Repeat unit
- A repeat unit is the specific group of atoms that appears over and over along a polymer chain.
- Addition polymerization
- Addition polymerization is a reaction in which monomers, often with carbon-carbon double bonds, link together without losing atoms as byproducts.
- Condensation polymerization
- Condensation polymerization is a reaction in which monomers join while releasing small molecules such as water or hydrogen chloride.
Common Mistakes to Avoid
- Confusing a monomer with a repeat unit is wrong because the repeat unit is the part found inside the polymer after bonding, and it may not look exactly like the original monomer.
- Assuming all polymerization produces water is wrong because addition polymerization usually forms no small byproduct.
- Writing polyethylene as repeated CH2=CH2 units is wrong because the carbon-carbon double bond opens during polymerization, giving the repeat unit [-CH2-CH2-].
- Thinking all polymers are synthetic plastics is wrong because natural polymers such as cellulose, proteins, starch, and DNA are essential biological materials.
Practice Questions
- 1 Ethene has molar mass 28.0 g/mol. If a polyethylene chain has 500 repeat units, what is the approximate molar mass of the chain?
- 2 A condensation polymer forms from 200 pairs of monomers, and each link releases 1 molecule of water. If 199 links form in one chain, how many water molecules are released?
- 3 Nylon is made by condensation polymerization, while polyethylene is made by addition polymerization. Explain one structural or reaction-based difference that lets you tell these two polymerization types apart.