Polymers · Grade 12
Polymers are very long molecules made by joining many small molecules, called monomers. Addition polymers are made from alkenes: the C=C double bond opens and the monomers join in a chain, with nothing else made. Condensation polymers are made from monomers with two functional groups; a small molecule such as water is given off each time two join. Many natural molecules are polymers: proteins, starch, cellulose and DNA.
Key facts
- Addition polymerisation: many alkene monomers join; the double bond opens. Ethene → poly(ethene), propene → poly(propene), chloroethene → poly(chloroethene) (PVC).
- The repeating unit is drawn in brackets with an n, and with bonds through the brackets.
- The Mᵣ of an addition polymer is n × the Mᵣ of the monomer: no atoms are lost.
- Condensation polymerisation: two kinds of functional group react and water (or another small molecule) is given off. A diol and a dicarboxylic acid make a polyester.
- Natural polymers: amino acids → proteins; glucose → starch and cellulose; nucleotides → DNA.
- Most addition polymers are not biodegradable, so reusing and recycling them matters.