4.4Unit 2 · Organic Chemistry
Synthetic polymers — Edexcel IGCSE Chemistry Modular - UNIT 2 Revision Notes & Topical Questions
5 min read 4 parts Lesson 4 of 4 1 quiz
Lesson summary
Draw repeat units of addition polymers from monomers, and vice versa.n CH2=CH2 → –[CH2–CH2]n–Addition polymers are saturatedthe C=C double bond opens to form single bonds.Polyester forms from a dicarboxylic acid + a diol with loss of water at each ester link.The ester link is –CO…
- Disposal of addition polymers
- Condensation polymers
- Polyester monomers
- Hydrolysis
- Water in polyester formation
- Biopolyesters
Section 1 of 4Synthetic polymers
Monomers
are small molecules. For addition polymers they are alkenes or substituted alkenes with a C=C bond; for condensation polymers each monomer has two reactive functional groups, one at each end.Addition polymers
under high pressure with a catalyst, the double bonds in many monomer molecules open and the carbons link into a long chain. No atoms are lost, so the polymer has the same empirical formula as the monomer.- Polymer names are made by putting 'poly' and brackets around the monomer name: propene → poly(propene). The repeat unit always has a two-carbon backbone for these monomers.
Disposal of addition polymers
they are inert, so microbes cannot break them down. Landfill uses land and they last for centuries. Incineration gives energy but releases CO2, and PVC gives toxic HCl. Recycling saves crude oil but needs sorting by type and can be costly.Condensation polymers
a dicarboxylic acid (HOOC–□–COOH) reacts with a diol (HO–□–OH). Each –COOH reacts with an –OH to form an ester link, releasing one H2O. Repeating this at both ends forms a polyester.- For each ester link formed, one water molecule is released; the repeat unit contains one acid residue and one diol residue.
- Some polyesters are biodegradable, and biopolyesters made from plant material are being developed to reduce plastic waste.
Polymers
are very large molecules with a high relative molecular mass, made from many monomers joined by covalent bonds. Synthetic polymers (e.g. plastics, nylon) are manufactured; natural polymers are made by living things.Polyester monomers
to find the monomers from a polyester, split each ester link (–COO–) at the C–O single bond. Add –OH to each C=O carbon to give the dicarboxylic acid, and add H to each oxygen to give the diol.Hydrolysis
is breaking a polymer or ester using water; it is the reverse of condensation. Adding water across each ester link turns a polyester back into its diol and dicarboxylic acid monomers.Water in polyester formation
each water molecule released is made from the –OH of a –COOH group in the acid and the H of an –OH group in the diol. Terylene (PET) is a common polyester made this way.Biopolyesters
are made by microorganisms from renewable sugars or plant oils. Microbes can break them down after use, so they reduce long-lasting plastic waste.
Section 2 of 4Process & sequence
- Identify the C=C double bond in the monomer.
- Draw the two carbon atoms with a single bond between them.
- Place the other atoms/groups above and below the carbons exactly as in the monomer.
- Draw bond lines extending out of each side of the carbon chain.
- Put brackets through these extending bonds and write n after them.
- To go back from polymer to monomer, remove brackets and n and restore the C=C bond.
Making a polyester — write these steps in this order; each step is a marking point.
- Dicarboxylic acid + diol
- –COOH meets –OH
- Ester link forms
- Water released
- Repeat at both ends
- Long polyester chain
Section 3 of 4Compare
| Monomer | Polymer | Use |
|---|---|---|
| Ethene, CH2=CH2 | Poly(ethene) | Plastic bags, bottles |
| Propene, CH2=CHCH3 | Poly(propene) | Crates, ropes |
| Chloroethene, CH2=CHCl | Poly(chloroethene), PVC | Window frames, pipes, cable insulation |
| Tetrafluoroethene, CF2=CF2 | PTFE | Non-stick pan coatings |
| Feature | Addition | Condensation |
|---|---|---|
| Monomers | Contain C=C | Two functional groups each (e.g. –COOH and –OH) |
| Number of products | One (polymer only) | Two (polymer + small molecule) |
| Example | Poly(ethene) | Polyester |
| Biodegradable? | No | Some polyesters are |
Section 4 of 4Worked examples
Draw (describe) the repeat unit of the polymer made from chloroethene, CH2=CHCl.
- Open the double bond: –[CH2–CHCl]n–, a two-carbon unit with H, H on one carbon and H, Cl on the other, bonds extending out through brackets.
- The polymer is poly(chloroethene).
- Open the double bond: –[CH2–CHCl]n–, a two-carbon unit with H, H on one carbon and H, Cl on the other, bonds extending out through brackets.
State two problems caused by disposing of poly(ethene) in landfill.
- It is non-biodegradable, so it remains for hundreds of years, and it takes up large amounts of land that could be used for other purposes.
Marked practiceQuizzes for this lesson
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