Key terms: Polymers

Learn each term as a precise definition, not a loose idea, in this chapter the exact wording is what earns the mark. Cover the definition, say it in your own words, then check. The terms are grouped by content standard so you can revise one section at a time.

12.1 Natural and synthetic polymers

• Polymer. A very large molecule (a macromolecule) built from many small repeating units joined by covalent bonds.
• Monomer. The small molecule that repeats to build a polymer; in an addition polymer it is an unsaturated molecule with a carbon–carbon double bond.
• Polymerisation. The chemical process in which many monomers join together to form a polymer.
• Repeating unit. The smallest part of a polymer that repeats along the chain, written inside brackets with a subscript n.
• Macromolecule. A molecule of very large molecular mass, made of hundreds or thousands of atoms; a polymer is one kind.
• Natural polymer. A polymer that occurs in living things, such as natural rubber, protein, starch, cellulose, silk and wool.
• Synthetic polymer. A polymer manufactured in industry, usually from petroleum products, such as polythene, PVC, polystyrene, nylon and Teflon.
• Isoprene. The monomer of natural rubber; natural rubber is poly(isoprene).
• Amino acid. The monomer of proteins; many amino acids join by condensation to form a protein.
• Glucose. The monomer of the carbohydrates starch and cellulose.

12.2 Types of polymerisation

• Addition polymerisation. Polymerisation in which unsaturated monomers (each with a C=C double bond) add directly to one another, so no other molecule is released.
• Condensation polymerisation. Polymerisation in which monomers with two functional groups join together, eliminating a small molecule (usually water) each time a bond forms.
• Unsaturated. Describing a molecule that contains a carbon–carbon double bond (C=C); addition monomers are unsaturated.
• Saturated. Describing a molecule with only single carbon–carbon bonds; an addition polymer chain is saturated because the double bonds have opened.
• Functional group. A reactive group of atoms in a molecule, such as –OH (hydroxyl), –COOH (carboxyl) or –NH₂ (amino); condensation monomers have two of them.
• By-product (of condensation). The small molecule eliminated during condensation polymerisation, most often water.
• Polyester. A condensation polymer whose chains are joined by ester links, made from a diol and a dicarboxylic acid; terylene is an example.
• Polyamide. A condensation polymer whose chains are joined by amide links; nylon is an example.

12.3 Natural rubber and vulcanisation

• Latex. A colloid in which rubber particles are dispersed in water, tapped from the rubber tree.
• Coagulation. The joining together of the dispersed rubber particles into a solid mass, caused by adding an acid that neutralises the charge on the particles.
• Poly(isoprene). The long-chain molecule of natural rubber, made of many isoprene units and containing carbon–carbon double bonds.
• Vulcanisation. The process of heating rubber with sulfur so that sulfur atoms form cross-links between the polymer chains.
• Cross-link (sulfur bridge). A bond of sulfur atoms formed between neighbouring rubber chains during vulcanisation, tying the chains together.
• Elasticity. The ability of a material to return to its original shape after being stretched; vulcanised rubber has greater elasticity than unvulcanised rubber.
• Elasticity limit. The greatest extension from which a material can still return to its original shape; vulcanisation raises the elasticity limit of rubber.

12.4 Uses and environmental issues of polymers

• Non-biodegradable. Describing a material that cannot be broken down by microorganisms, so it stays in the environment for a very long time; most synthetic polymers are non-biodegradable.
• Biodegradable plastic. A plastic designed to be broken down by microorganisms, reducing the build-up of waste.
• Photodegradable plastic. A plastic designed to break down when exposed to light, especially sunlight.
• Recycling. Reprocessing waste plastic into new products, one of the main responses to plastic waste, alongside reducing and reusing.
• Open burning. Burning waste in the open air; open burning of PVC releases hydrogen chloride, an acidic corrosive gas, and incomplete burning of plastics releases poisonous carbon monoxide and soot.

Seeing the terms in context

Definitions are easiest to hold onto when you see how the terms link. A monomer is one small molecule; polymerisation joins many of them into a polymer, which is a macromolecule whose repeating unit you can write in brackets. If the monomer is unsaturated, the join is addition polymerisation and no by-product is released; if the monomer has two functional groups, the join is condensation polymerisation and a small molecule such as water is eliminated, giving a polyester or a polyamide. In natural rubber, latex carries poly(isoprene) particles that coagulate when acid is added; vulcanisation then forms sulfur cross-links that raise the elasticity limit. Finally, because most synthetic polymers are non-biodegradable, the answers are recycling, biodegradable plastic and photodegradable plastic, and avoiding open burning. Reading the terms as one connected story makes each definition far easier to recall under exam pressure.

How to use this glossary

Read each term with its definition, then cover the definition and rebuild it from the term alone. Pay special attention to the pairs that students confuse: addition versus condensation, saturated versus unsaturated, biodegradable versus non-biodegradable, and coagulation versus vulcanisation. Being able to write the exact definition of monomer, polymerisation, cross-link and non-biodegradable protects easy marks throughout the chapter. A one-to-one teacher can test you on these definitions and correct any that are slightly off, which is where marks quietly slip away.

Because the Polymers vocabulary reappears across the SPM Chemistry written papers, in structured questions, in the extended-response essays and even in multiple-choice items, securing the exact wording now is one of the highest-return pieces of revision you can do for this chapter. Keep this glossary beside the revision notes and the worked examples, and add any term your own past-paper practice throws up, so your personal list grows to match the questions you meet.