What are polymers and how are they classified in Edexcel IGCSE Chemistry?

Polymers are large molecules made up of repeating structural units called monomers. In Edexcel IGCSE Chemistry, polymers are classified into natural polymers, like proteins and cellulose, and synthetic polymers, such as plastics like polyethylene and polystyrene. Understanding the classification helps in studying their properties and applications.

How are addition polymers formed in organic chemistry?

Addition polymers are formed through a process called addition polymerization, where unsaturated monomers, typically alkenes, join together without the loss of any small molecules. This process involves the breaking of double bonds in the monomers to form long chains. An example is the polymerization of ethene to form polyethylene.

What is the difference between addition and condensation polymerization?

In addition polymerization, monomers add together without the loss of any atoms, typically involving alkenes. In contrast, condensation polymerization involves the joining of monomers with the elimination of small molecules like water or methanol. This process is common in the formation of polyesters and polyamides.

Why are polymers important in everyday life according to the IGCSE Chemistry curriculum?

Polymers are crucial in everyday life due to their diverse applications and properties. They are used in making plastics, textiles, and even in medical devices. The IGCSE Chemistry curriculum highlights their importance in understanding material science and the impact of synthetic polymers on the environment.

What environmental issues are associated with polymers, as discussed in Edexcel IGCSE Chemistry?

Polymers, particularly synthetic ones like plastics, pose significant environmental issues due to their non-biodegradable nature. They contribute to pollution and waste management challenges. The Edexcel IGCSE Chemistry curriculum discusses the importance of recycling and developing biodegradable polymers to mitigate these environmental impacts.

Why is "Drawing the repeat unit with the C=C double bond still present" a common mistake in Polymers?

Why it happens: Copying the monomer too literally. How to avoid it: Addition polymerisation OPENS the C=C double bond → in the repeat unit, it becomes a C–C SINGLE bond. Always draw the repeat unit with a SINGLE bond between the two main-chain carbons. Example: ethene CH₂=CH₂ → repeat unit ─(CH₂–CH₂)ₙ─ (single bond). Source: 4CH1 Examiner Reports 2022-2024

Why is "Drawing the repeat unit without square brackets and subscript n" a common mistake in Polymers?

Why it happens: Drawing just the chain. How to avoid it: ALWAYS include the square brackets [...] and the subscript n (outside the brackets) → tells the marker this is a repeating unit. Without brackets, you've drawn a small molecule, not a polymer's repeat unit. Source: 4CH1 Examiner Reports 2023-2024

Why is "Writing a condensation polymerisation equation without the water byproduct" a common mistake in Polymers?

Why it happens: Treating it like addition. How to avoid it: Condensation polymerisation ALWAYS produces a small molecule (usually water) per linkage. For n diacid + n diol → polymer + 2n H₂O. Don't forget the byproduct. Source: 4CH1 Examiner Reports 2023-2024

Why is "Saying condensation polymerisation uses one monomer" a common mistake in Polymers?

Why it happens: Confusion with addition. How to avoid it: Addition: ONE monomer (alkene). Condensation: TWO different monomers (each with two functional groups). Some condensation polymers (e.g. silk, polyglycolic acid from one monomer with both –COOH and –OH) seem to use one monomer, but most 4CH1 examples (Terylene from diacid + diol; nylon-6,6 from diacid + diamine) clearly use two different monomers. Source: 4CH1 Examiner Reports 2022-2024

Why is "Confusing 'non-biodegradable' with 'cannot be recycled'" a common mistake in Polymers?

Why it happens: Both relate to disposal. How to avoid it: **Non-biodegradable**: microorganisms don't break it down. Persists for centuries. **Recyclable**: can be melted and re-moulded into new products (some plastics, like PET and HDPE, are widely recycled). A polymer can be both non-biodegradable AND recyclable (most addition polymers fit this — they don't decompose naturally but can be melt-recycled).

Why is "Saying 'incinerating poly(ethene) releases HCl'" a common mistake in Polymers?

Why it happens: Confusion with PVC. How to avoid it: ONLY PVC (poly(chloroethene)) and chlorinated polymers release HCl on incineration — because they CONTAIN chlorine atoms in the repeat unit. Poly(ethene) (just C and H) releases CO₂ + H₂O (clean burn) + soot (incomplete combustion). PTFE releases fluorinated gases. The polymer's incineration products depend on its atoms. Source: 4CH1 Examiner Reports 2023-2024

Organic ChemistryEdexcel IGCSE Chemistry (4CH1)

Polymers

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Polymers — Pearson Edexcel International GCSE Chemistry 4CH1 Study Notes (2026 onwards, Spec Issue 4)

POLYMERS are very long molecules made by joining many MONOMERS via POLYMERISATION. Two main types: (1) ADDITION POLYMERISATION (Paper 1 core) — alkene monomers (with C=C) open their double bonds and join end-to-end with NO atoms lost. Examples: poly(ethene) from ethene (plastic bags, bottles); poly(propene) from propene (containers, fibres); PVC = poly(chloroethene) from chloroethene (pipes, frames); PTFE from tetrafluoroethene (non-stick coatings). To find repeat unit: open C=C of monomer, draw in brackets with n. To find monomer from repeat unit: close the C–C between repeating units back to C=C. (2) CONDENSATION POLYMERISATION (Paper 2, P content) — TWO monomers with TWO functional groups each, joining with loss of a small molecule (water). Polyesters (Terylene/PET) from diacid + diol → clothing fibres + drinks bottles. Polyamides (nylon) from diacid + diamine → ropes + clothing. Environmental impact: addition polymers NON-BIODEGRADABLE → landfill, ocean pollution, microplastics. Disposal: landfill (poor), incineration (CO₂ + HCl from PVC), recycling (limited). Strategies: reduce, reuse, recycle, biodegradable plastics.

At a glance

Polymer = LARGE molecule made of MANY repeating units (monomers).
Monomer = small molecule that joins to form a polymer.
Polymerisation = the reaction joining monomers.
Addition polymerisation (core, Paper 1): alkene monomers (C=C) open up; no atoms lost.
• Ethene → poly(ethene): bags, bottles, films.
• Propene → poly(propene): containers, fibres.
• Chloroethene (CH₂=CHCl) → PVC: pipes, frames, cable insulation.
• Tetrafluoroethene → PTFE: non-stick coatings (Teflon).
Find repeat unit: open C=C of monomer; draw in brackets [...] with subscript n.
Find monomer from polymer: close the C–C between repeat units back to C=C.
Condensation polymerisation (Paper 2 only): TWO monomers, each with 2 functional groups, join with LOSS OF SMALL MOLECULE (water).
• Polyesters: diacid + diol → ester linkages + n H₂O. e.g. Terylene / PET (clothing fibres, drinks bottles).
• Polyamides: diacid + diamine → amide linkages + n H₂O. e.g. Nylon-6,6 (ropes, clothing, parachutes).
Environment: addition polymers NON-BIODEGRADABLE → landfill, ocean pollution.
Disposal: landfill (poor), incineration (CO₂ + HCl from PVC), recycling (sort by type 1-7).
Solutions: reduce + reuse + recycle; biodegradable plastics (PLA from corn starch); plant-based polymers.

What you’ll learn

Mapped to the Cambridge IGCSE 4CH1 syllabus (2026 onwards).

4.37 — Recall the meanings of POLYMER, MONOMER, and POLYMERISATION.
4.38 — Describe ADDITION POLYMERISATION: alkene monomers (containing C=C) open their double bonds to form long polymer chains with NO atoms lost.
4.39 — Given a monomer (e.g. ethene, propene, chloroethene), write the equation for polymerisation and draw the repeat unit. Conversely, given a repeat unit, identify the monomer.
4.40 — Recall the uses of common addition polymers: poly(ethene) for bags + bottles; poly(propene) for containers + fibres; poly(chloroethene) = PVC for pipes + frames; poly(tetrafluoroethene) = PTFE for non-stick coatings.
4.41 — Understand the environmental impact of addition polymers: non-biodegradability; problems with landfill, incineration, and recycling; potential solutions.
4.42P — (Paper 2) Describe CONDENSATION POLYMERISATION: TWO monomers, each with TWO functional groups, joining with loss of a SMALL MOLECULE (usually water). Examples: polyesters from diacid + diol; polyamides from diacid + diamine.
4.43P — (Paper 2) Compare addition polymerisation and condensation polymerisation: monomer types, functional groups, byproducts, mechanism.
4.44P — (Paper 2) Recall examples of natural condensation polymers (proteins, DNA, cellulose) and their relevance to biology.

Polymer basics — monomers, polymers, and polymerisation (spec 4.37)

Polymer = long molecule from many monomers. Polymerisation = joining reaction. Two types: addition + condensation.

A POLYMER is a very large molecule made up of MANY smaller repeating units (called MONOMERS) joined together by chemical bonds.

Typical polymer molecules have THOUSANDS of monomers per chain (n = 100 to > 1,000,000).
Molecular masses can reach into the millions.
Polymers can be SYNTHETIC (e.g. poly(ethene), nylon, PVC — made in factories) or NATURAL (e.g. proteins, DNA, cellulose, starch — made by living organisms).

A MONOMER is the small molecule that joins repeatedly to make the polymer. The monomer's structure determines the polymer's properties.

POLYMERISATION is the chemical reaction by which monomers join.

Two main types of polymerisation.

Feature	Addition	Condensation
Number of monomer types	ONE (alkene)	TWO (each with 2 functional groups)
Monomer functional group	C=C double bond	–COOH + –OH or –COOH + –NH₂
Byproduct	NONE	Water (or HCl) at each linkage
Bond formed	C–C in backbone	Ester (–COO–) or amide (–CONH–)
Polymer backbone	All-carbon	Carbon + heteroatom links
Examples	Poly(ethene), PVC, polystyrene	Terylene, nylon, proteins, DNA
Biodegradable?	Usually NO	Some are (esters + amides can hydrolyse)

For 4CH1 Paper 1: focus on ADDITION polymerisation (compulsory). For 4CH1 Paper 2: also CONDENSATION polymerisation (P-designated content).

Why polymers are so important in modern life.

Without polymers, we would not have:

Plastic bags, bottles, containers, packaging.
Synthetic fibres (clothing, ropes, carpets).
Electrical cable insulation.
Non-stick cookware coatings.
Most cosmetics, paints, adhesives.
Many pharmaceuticals (drug delivery polymers).
Almost any modern construction or transport material.

The plastic age began in the early 20th century with Bakelite (a phenol-formaldehyde polymer), and exploded after WWII with the petrochemical industry. Today the world produces > 400 million tonnes of plastic per year.

The general polymer equation.

For any polymerisation, the equation has the structure:

$n \text{(monomer)} \rightarrow \text{(polymer of n repeat units)} + \text{(byproducts, if any)}$

The 'n' represents 'many' — typically thousands of monomers per chain. In equations, we use 'n' as a symbolic placeholder for a large number.

The repeat unit concept.

A polymer is too long to draw in full. Instead, we draw ONE REPEAT UNIT in square brackets [ ... ] with the subscript 'n' outside:

  ┌──── repeat unit ────┐
  [                     ]
                         n

The brackets mark the boundaries; the n means 'this unit is repeated many times to give the polymer'.

To DRAW a repeat unit from a monomer (for addition polymerisation):

Take ONE monomer.
Open the C=C double bond.
Draw the result in square brackets with subscript n outside.
Extend bonds from each end of the unit to indicate connection to neighbours.

To IDENTIFY the monomer from a repeat unit:

Look at the repeat unit between the brackets.
CLOSE the bond between the two main-chain carbons back to a C=C.
The result is the monomer.

Quick examples.

Monomer	Repeat unit (addition)
CH₂=CH₂ (ethene)	─(CH₂–CH₂)ₙ─
CH₂=CHCH₃ (propene)	─(CH₂–CH(CH₃))ₙ─
CH₂=CHCl (chloroethene)	─(CH₂–CHCl)ₙ─
CF₂=CF₂ (tetrafluoroethene)	─(CF₂–CF₂)ₙ─
CH₂=CHC₆H₅ (styrene)	─(CH₂–CH(C₆H₅))ₙ─

In each case: the C=C of the monomer becomes a C–C in the repeat unit; the two carbons of the former C=C are joined to neighbours via single bonds.

Polymer = large molecule from many monomers (typically 100-1,000,000 per chain).
Monomer = the small unit that joins repeatedly.
Polymerisation = the reaction joining monomers.
Two types: addition (alkene monomer, no atoms lost) + condensation (2 monomers, small molecule lost).
Repeat unit drawn in square brackets [...] with subscript n outside.
From monomer to repeat unit: open C=C; from repeat unit to monomer: close C–C back to C=C.
Without polymers, no modern plastics, fibres, packaging, electronics — entire industry depends on them.

See the full worked example for polymers →

Addition polymerisation (spec 4.38, 4.39)

Alkene monomers (C=C) open up and join. No atoms lost. Poly(ethene), poly(propene), PVC, PTFE.

ADDITION POLYMERISATION is a type of polymerisation in which many alkene monomers (containing C=C double bonds) join together by opening their double bonds. NO atoms are lost during the joining — the polymer is the sum of all the monomers' atoms.

The general equation.

$n\,\text{CH}_2{=}\text{CHR} \rightarrow {-}(\text{CH}_2{-}\text{CHR})_n{-}$

(where R can be H, CH₃, Cl, F, C₆H₅, etc., depending on which monomer)

Mechanism — what happens during polymerisation.

The C=C π bond breaks (the weaker of the two bonds in the double bond — see Topic 4.4).
The carbon atoms at the former double bond now have one 'free' bonding position each.
Each carbon bonds to a carbon of an adjacent monomer — extending the chain in both directions.
The σ bond between the two original C atoms is retained as a C–C single bond.
Result: a long chain of –CH₂–CHR– units, where the original C=C bonds have become C–C single bonds, and the original 'side' atoms of each monomer (the H, R groups) are now side groups on the polymer chain.

Detailed mechanism (free radical, beyond 4CH1 but useful).

For LDPE production from ethene:

An organic peroxide initiator decomposes thermally: R-O-O-R → 2 R-O•.
The radical attacks one ethene molecule: R-O• + CH₂=CH₂ → R-O-CH₂-CH₂•.
The new radical attacks another ethene: R-O-CH₂-CH₂• + CH₂=CH₂ → R-O-CH₂-CH₂-CH₂-CH₂•.
Each step adds another –CH₂–CH₂– unit. The radical 'walks' down the chain.
Termination — two growing chains meet end-to-end and join, killing the radicals.
Sometimes branching occurs (the radical reaches back into the chain) — this gives LDPE its branched structure.

This is one of several mechanisms for addition polymerisation (free radical, Ziegler-Natta, metallocene, anionic, cationic) — they all produce the same basic polymer with subtle differences in chain structure.

Why addition polymerisation works.

The C=C double bond is ENERGETICALLY favourable to break (the π bond is weaker than the σ bond, about 264 kJ/mol vs 348 kJ/mol). The new C–C bonds formed between monomers are normal strong C–C single bonds. So the overall reaction is exothermic and irreversible under normal conditions.

Common addition polymers — table.

Monomer	Repeat unit	Polymer name	Uses
CH₂=CH₂ (ethene)	─(CH₂–CH₂)ₙ─	Poly(ethene) = polythene = PE	Plastic bags, bottles, films, pipes, crates
CH₂=CHCH₃ (propene)	─(CH₂–CH(CH₃))ₙ─	Poly(propene) = polypropylene = PP	Containers, fibres, ropes, car parts, bottle caps
CH₂=CHCl (chloroethene / vinyl chloride)	─(CH₂–CHCl)ₙ─	Poly(chloroethene) = PVC	Pipes, window frames (uPVC), cable insulation, flooring, records
CF₂=CF₂ (tetrafluoroethene)	─(CF₂–CF₂)ₙ─	Poly(tetrafluoroethene) = PTFE = Teflon	Non-stick frying pans, plumbing tape, gore-tex
CH₂=CH-C₆H₅ (styrene)	─(CH₂–CH(C₆H₅))ₙ─	Polystyrene = PS	Packaging foam, insulation, plastic cutlery

Industrial production of poly(ethene).

Two distinct conditions give two distinct products:

LDPE (low-density poly(ethene)):

High T (~ 200 °C), high P (~ 1500 atm).
Organic peroxide initiator (free radical).
BRANCHED chains (random branches grow from the main chain).
Branches prevent close packing → low density (~ 0.92 g/cm³).
SOFT, FLEXIBLE plastic.
Uses: plastic bags, cling film, squeezy bottles.

HDPE (high-density poly(ethene)):

Lower T (~ 50-80 °C), lower P (~ 1-10 atm).
Ziegler-Natta catalyst (titanium chloride + aluminium alkyl).
LINEAR chains (no branching).
Tight packing → higher density (~ 0.95 g/cm³).
HARDER, STRONGER plastic.
Uses: milk jugs, detergent bottles, water pipes, hard hats, crates.

The choice of conditions controls the polymer structure → controls the properties.

Repeat unit drawing — common errors.

When drawing a repeat unit:

ALWAYS include the square brackets [...] with subscript n outside.
The bond between the two main-chain carbons should be SINGLE (C–C), not double (C=C). Addition polymerisation BREAKS the C=C.
Extend bonds from each end of the unit to indicate connection to neighbours.
Include all H atoms and side groups (e.g. Cl in PVC, CH₃ in PP).

Incorrect repeat unit examples:

─(CH₂=CH₂)ₙ─ — C=C still present (wrong: should be C–C).
─(CH₂–CHCl) without brackets and n — just a piece of chain (not a repeat unit).

Finding the monomer from a repeat unit.

Reverse of the above. Given a repeat unit, work out the monomer:

Look at the repeat unit between the brackets.
Identify the two carbons in the main chain (these were the C=C of the monomer).
Close the C–C between them back to a C=C.
Add any necessary H atoms (sometimes the repeat unit drawing omits some).
The result is the monomer (with C=C double bond restored).

Example.

Given repeat unit ─(CH₂–CHCl)ₙ─:

Main-chain carbons: CH₂ (left) and CHCl (right).
Close the C–C to a C=C: CH₂=CHCl.
Monomer: chloroethene (vinyl chloride). ✓

Uses of common addition polymers.

Poly(ethene):

LDPE: plastic bags, cling film, squeezy bottles, food wrap, plastic sheeting.
HDPE: milk jugs, detergent bottles, water pipes, plastic crates, hard hats, plastic chairs.
The most-produced plastic in the world (~ 100 million tonnes/year).

Poly(propene):

Yoghurt pots, takeaway containers, microwave-safe containers (higher mp than PE).
Ropes, twine, fibres for carpets, woven bags.
Bottle caps (twist-off types).
Car parts (bumpers, dashboards, interior trims).
Living hinges (shampoo flip-top caps).
Medical: syringes, lab equipment (can be autoclaved).

PVC (poly(chloroethene)):

Rigid PVC (uPVC): pipes for plumbing + drainage, window frames, doors.
Flexible PVC (with phthalate plasticisers): cable insulation, flooring (vinyl tiles), imitation leather, raincoats, IV bags (medical).
Historical: vinyl records.

PTFE (Teflon):

Non-stick coatings on cookware (frying pans).
Plumbing tape (white thread-sealing tape).
Gore-tex membranes (waterproof + breathable fabrics).
Insulation for high-temperature wiring.
Chemical-resistant linings for tanks + pipes.

Why PTFE is non-stick: the C-F bonds are very strong (498 kJ/mol) and the F atoms shield the C atoms from approaching molecules → very low surface adhesion → nothing sticks.

Polystyrene:

Packaging foam (expanded polystyrene = Styrofoam).
Insulation (in buildings + appliances).
Plastic cutlery + cups.
CD cases (rigid form).

Properties common to addition polymers.

Stable — all-carbon backbones are very strong → won't easily decompose.
Inert — don't react with most chemicals at room T.
Tough — long chains entangle → resists tearing.
Mouldable — can be shaped by heat / pressure.
Cheap — made from abundant petrochemical alkenes.
NON-BIODEGRADABLE — no functional groups for bacteria to attack.
THERMOPLASTIC — soften on heating; can be re-moulded (allows recycling).
Electrically insulating (except specially-doped ones for electronic uses).

The link to alkenes (Topic 4.4).

Addition polymerisation is just an extension of the addition reactions of alkenes:

Br₂ + alkene → 1,2-dibromoalkane (Topic 4.4).
HBr + alkene → bromoalkane (Topic 4.4).
H₂ + alkene → alkane (hydrogenation, Topic 4.4).
Many alkene molecules + each other → polymer (Topic 4.8, this section).

In each case, the C=C opens up and new bonds form. The 'polymer' addition is unique because the same kind of molecule adds repeatedly to itself, giving a long chain.

Edexcel exam tip.

A typical 4CH1 question on addition polymers:

Give you a monomer (e.g. propene) → ask for the equation + repeat unit.
Give you a repeat unit → ask for the monomer name + a use.
Ask why addition polymers are non-biodegradable.

For 1+2: master the open/close C=C technique. For 3: mention the strong C–C backbone with no functional groups for bacteria to attack.

Mark scheme keywords:

'Many monomer molecules' or 'n monomers'.
'C=C double bond opens / breaks'.
'No atoms lost' or 'no other product'.
'Repeat unit' drawn with brackets and subscript n.

Addition polymerisation: alkene monomers (C=C) join end-to-end; no atoms lost.
C=C double bond opens; new C–C bonds form to neighbours.
Repeat unit drawn in square brackets [...] with subscript n; C=C now C–C.
Common polymers: PE (bags), PP (containers), PVC (pipes), PTFE (Teflon non-stick).
LDPE vs HDPE: high T+P branched soft vs low T+P linear strong.
Find monomer from repeat unit: close C–C between main-chain carbons back to C=C.
Properties: stable, tough, inert, mouldable, cheap, NON-biodegradable.
100 million tonnes of poly(ethene) per year — the most-produced plastic.

See the full worked example for polymers →

Condensation polymerisation — polyesters and polyamides (spec 4.42P, 4.43P)

TWO monomers with 2 functional groups each. Loss of H₂O per linkage. Polyesters (Terylene/PET) + polyamides (nylon).

CONDENSATION POLYMERISATION is a type of polymerisation in which TWO DIFFERENT monomers, each with TWO functional groups (one at each end), join together with the LOSS OF A SMALL MOLECULE (usually water) at each new linkage. Many monomers join → long polymer chain + many small molecules.

(Paper 2 content for 4CH1 — designated P statements.)

The two functional groups required.

For condensation polymerisation, each monomer needs to react on BOTH ends → it must have TWO functional groups (one at each end of the molecule).

Polymer type	Monomer 1	Monomer 2	Linkage formed	Small molecule lost
Polyester	Dicarboxylic acid (HOOC-X-COOH)	Diol (HO-Y-OH)	Ester (–COO–)	Water (H₂O)
Polyamide	Dicarboxylic acid (HOOC-X-COOH)	Diamine (H₂N-Y-NH₂)	Amide (–CONH–)	Water (H₂O)

General polyester equation.

$n\,\text{HOOC-X-COOH} + n\,\text{HO-Y-OH} \rightarrow {-}(\text{CO-X-COO-Y-O})_n{-} + 2n\,\text{H}_2\text{O}$

Each ester linkage requires:

The –OH of the acid (provides the OH of water).
The –H of the alcohol (provides the H of water).
The remaining C(=O)–O bonds together as the ester linkage.

Each repeat unit has TWO ester linkages (one between the diacid and the diol on each side) → 2n water molecules eliminated for n diacid + n diol.

Specific example: Terylene (PET).

Terylene is the most common polyester, also called PET (poly(ethylene terephthalate)).

Monomer 1: benzene-1,4-dicarboxylic acid (terephthalic acid) — HOOC-C₆H₄-COOH (where C₆H₄ is the benzene ring with the two COOH groups in para position).
Monomer 2: ethane-1,2-diol (ethylene glycol) — HO-CH₂-CH₂-OH.

Equation:

$n\,\text{HOOC-C}_6\text{H}_4\text{-COOH} + n\,\text{HO-CH}_2\text{CH}_2\text{-OH} \rightarrow {-}(\text{CO-C}_6\text{H}_4\text{-COO-CH}_2\text{CH}_2\text{-O})_n{-} + 2n\,\text{H}_2\text{O}$

Repeat unit:

─CO–C₆H₄–COO–CH₂CH₂–O─    (× n times)
  └── acid half ──┘  └─ alcohol half ─┘

The benzene ring (from terephthalic acid) alternates with the ethylene glycol units, joined by ester linkages.

Uses of Terylene / PET.

Clothing fibres: Terylene (UK name) is used in shirts, suits, trousers — often blended with cotton. Durable, easy-care, wrinkle-resistant, holds dye well.
PET drinks bottles: clear, lightweight, shatter-resistant, BPA-free — for water, soft drinks, juice. Recycling code 1.
Photographic film: Mylar (a PET film).
Sails for yachts: high tensile strength, doesn't stretch.
Conveyor belts and reinforcement fibres: heavy-duty applications.
Polyester thread: sewing thread.

The fibre form is called Terylene (also Dacron in USA); the bottle form is called PET. Same chemical, different physical form depending on processing.

General polyamide equation.

$n\,\text{HOOC-X-COOH} + n\,\text{H}_2\text{N-Y-NH}_2 \rightarrow {-}(\text{CO-X-CONH-Y-NH})_n{-} + 2n\,\text{H}_2\text{O}$

Each amide linkage (–CONH–) forms with loss of water:

The –OH of the acid + the –H of the amine = H₂O.
The remaining –CO– bonds to –NH– to form the amide.

Specific example: Nylon-6,6.

The number '6,6' refers to the carbon counts in the two monomers — both have 6 carbons.

Monomer 1: hexanedioic acid (adipic acid) — HOOC-(CH₂)₄-COOH (6 carbons including the two COOH).
Monomer 2: hexane-1,6-diamine — H₂N-(CH₂)₆-NH₂ (6 carbons + 2 N).

Equation:

$n\,\text{HOOC-(CH}_2)_4\text{-COOH} + n\,\text{H}_2\text{N-(CH}_2)_6\text{-NH}_2 \rightarrow {-}(\text{CO-(CH}_2)_4\text{-CONH-(CH}_2)_6\text{-NH})_n{-} + 2n\,\text{H}_2\text{O}$

Uses of Nylon.

Clothing: strong, durable synthetic fibre — used in stockings, swimwear, sportswear, jackets.
Ropes and lines: high tensile strength + low stretch — fishing line, climbing rope, parachute cord.
Carpets: wear-resistant synthetic fibre.
Tyre cords: reinforcement in car/truck tyres.
Toothbrush bristles: stiff but flexible.
Engineering plastics: nylon gears, bearings (low friction, durable).

Nylon was invented in the 1930s by Wallace Carothers at DuPont — one of the great industrial chemistry breakthroughs of the 20th century.

Comparison: addition vs condensation polymerisation.

Feature	Addition	Condensation
Monomer types	ONE (alkene)	TWO (each with 2 functional groups)
Functional group on monomer	C=C double bond	–COOH + –OH (polyester) or –COOH + –NH₂ (polyamide)
Bond breaking	π bond of C=C	O-H of acid + H of alcohol/amine
Bond forming in polymer	C–C single	Ester (–COO–) or amide (–CONH–)
Byproduct	NONE	Small molecule (usually H₂O) per linkage
Atom economy	100%	< 100% (atoms lost as water)
Polymer backbone	All carbon	Carbon + heteroatom links (O or N)
Biodegradable?	Usually NO (no functional groups for microbes)	Often YES (ester/amide can be hydrolysed)
Recyclable?	Yes (melt-and-mould thermoplastics)	Yes (can be chemically hydrolysed back to monomers + recycled)
Examples	PE, PP, PVC, PTFE, polystyrene	Terylene/PET, Nylon, polylactic acid, proteins, DNA, cellulose

Natural condensation polymers.

Many of the most important biological molecules are CONDENSATION POLYMERS:

Proteins: amino acids join via PEPTIDE BONDS (a type of amide bond, –CONH–) with loss of water. Each peptide bond forms between the –COOH of one amino acid and the –NH₂ of another. Proteins are essentially POLYAMIDES with side chains of varying chemistry.
DNA / RNA: nucleotides join via PHOSPHODIESTER BONDS with loss of water. Each phosphodiester bond is a double-ester between the phosphate group of one nucleotide and the hydroxyl of another.
CELLULOSE (plant cell walls): glucose units join via GLYCOSIDIC BONDS — each bond between the –OH of one glucose and the –OH of another, with loss of water. Cellulose is a condensation polymer of glucose.
STARCH (energy storage in plants): same as cellulose chemically (glucose monomers + glycosidic bonds + water lost) but different geometry.
PROTEINS-in-detail: silk, wool, gelatin, collagen — all natural polyamides made by living organisms.

So the chemistry of condensation polymerisation is universal — it operates both in industrial polyester / nylon factories AND in every living cell forming proteins, DNA, and structural carbohydrates.

Biodegradability — why condensation polymers can be greener.

The ester (–COO–) and amide (–CONH–) linkages in condensation polymers can be HYDROLYSED by water, acid, alkali, or enzymes (e.g. esterases, proteases in microorganisms). This means:

Some condensation polymers naturally biodegrade in the environment over months to years (e.g. polylactic acid PLA, polyhydroxyalkanoates PHA).
Recycling can be done by CHEMICAL HYDROLYSIS — break the polymer back to its monomers, then re-polymerise.
Biological polymers (proteins, DNA, cellulose) are inherently biodegradable — microbes have evolved enzymes to break them down.

Addition polymers (all-C–C backbone, no functional groups) lack this advantage → much harder to biodegrade or recycle chemically.

Polylactic acid (PLA) — a modern green polymer.

PLA is made from LACTIC ACID (CH₃CH(OH)COOH), which has both –COOH AND –OH on the SAME molecule. It can polymerise with itself:

$n\,\text{CH}_3\text{CH(OH)COOH} \rightarrow {-}(\text{CH}_3\text{CH-COO})_n{-} + n\,\text{H}_2\text{O}$

Lactic acid comes from FERMENTATION of corn starch or sugar cane — renewable!

PLA is:

Bioderived — from plants, not crude oil.
Biodegradable — composts in 6 months in industrial composters (slower in normal landfill).
Versatile — used for food packaging (clear cups, biodegradable cutlery), 3D printing filament, medical sutures (dissolves in the body).

PLA is one of the leading 'green' polymer alternatives to traditional petrochemical plastics.

Edexcel exam tip.

Paper 2 questions on condensation polymerisation typically:

Ask you to identify the two monomer types (diacid + diol for polyester; diacid + diamine for polyamide).
Show a generic equation with the small molecule eliminated.
Compare with addition polymerisation.
Give an example polymer and its use.

Mark scheme keywords:

'Two different monomers'.
'Each monomer has two functional groups'.
'Small molecule eliminated' or 'water released'.
'Ester linkage (–COO–)' for polyesters.
'Amide linkage (–CONH–)' for polyamides.

Use these in your answers.

Condensation polymerisation: 2 monomers (each with 2 functional groups) + loss of small molecule.
Polyesters: diacid + diol → ester linkages + n H₂O. e.g. Terylene/PET (clothing, drinks bottles).
Polyamides: diacid + diamine → amide linkages + n H₂O. e.g. nylon-6,6 (ropes, clothing).
Atom economy < 100% (atoms lost as water).
Polymer backbones have O (ester) or N (amide) atoms in addition to C.
Natural condensation polymers: proteins (peptide bonds), DNA (phosphodiester), cellulose (glycosidic).
More biodegradable than addition polymers — ester/amide bonds can be hydrolysed.
PLA (polylactic acid) = modern green biopolymer from fermentation, biodegradable.

See the full worked example for polymers →

Environmental impact of polymers (spec 4.41)

Most plastics non-biodegradable → landfill, oceans, microplastics. Disposal: landfill, incineration, recycling. Solutions: reduce/reuse/recycle/biodegradable.

Polymers are central to modern life but their disposal causes major environmental problems. Understanding the chemistry of WHY plastics persist is key to understanding the environmental impact and possible solutions.

Why addition polymers persist in the environment.

Addition polymers (poly(ethene), PP, PVC, PTFE, polystyrene) have ALL-CARBON BACKBONES with strong C–C and C–H bonds. They have NO functional groups that microorganisms can easily attack:

No –COOH (carboxylic acid) for esterases to cleave.
No –OH (alcohol) for hydroxylases.
No –NH (amide) for proteases.
No glycosidic bonds for cellulases.

So bacteria, fungi, and other decomposers cannot break them down. The plastic just sits there for hundreds of years.

Estimated decomposition times in landfill:

Material	Decomposition time
Banana peel	1 month
Cotton T-shirt	6 months
Newspaper	1 year
Cardboard	5 years
Aluminium can	80-200 years
Plastic bag (LDPE)	500-1000 years
Plastic bottle (PET)	450 years
Polystyrene foam	Indefinite (essentially)
Glass bottle	1 million years

Plastics are the most persistent of common waste materials.

Other factors:

Sunlight (UV) can break plastic chains slowly over decades, but the resulting pieces are still non-biodegradable.
Heat doesn't degrade plastics significantly (they melt and re-solidify on cooling — thermoplastic behaviour).
Chemical degradation requires very aggressive conditions not normally found in nature.

Disposal option 1: Landfill.

Most plastic waste (~ 60-70% globally) ends up in LANDFILL — buried in pits.

Problems:

Takes up SPACE permanently.
Doesn't decompose → landfill capacity is permanently lost.
LEACHING of additives (plasticisers, flame retardants, dyes) into groundwater.
Microplastics can escape into soils and surrounding waters.
Visual blight and methane release (from co-buried organic waste).
Limited by available land (countries with little space can't keep using landfill forever).

Disposal option 2: Incineration.

Burning plastics in modern waste-to-energy plants.

Advantages:

Massively REDUCES VOLUME (95-99% mass reduction).
Recovers ENERGY (electricity / heat — offsets fossil fuel use).
Avoids landfill space problem.

Problems:

CO₂ emissions — burning plastic releases CO₂ (greenhouse gas). The carbon was originally from crude oil — releasing it adds to atmospheric CO₂.
PVC produces TOXIC GASES when burnt: $\text{─(CH}_2\text{CHCl)─}_n + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{HCl} + \text{traces of dioxins}$ HCl (hydrogen chloride) is acidic, corrosive, and contributes to acid rain. Dioxins are extremely toxic organic pollutants (need very high T + good mixing to avoid).
POLYSTYRENE + other polymers can produce STYRENE + other toxic monomers if not burnt completely.
Particulate matter → air pollution.
Modern incinerators have scrubbers to remove HCl and SO₂, but emissions are not zero.

So incineration is useful but must be done in MODERN, well-controlled plants. Older incinerators in developing countries can release significant pollution.

Disposal option 3: Recycling.

Sorting plastic waste by type (using the recycling code 1-7), washing, grinding, melting, and re-moulding into new products.

The recycling code system.

Code	Polymer	Common uses
1	PET	Drinks bottles, polyester clothing
2	HDPE	Milk jugs, detergent bottles
3	PVC	Pipes, window frames
4	LDPE	Plastic bags, films
5	PP	Containers, fibres, bottle caps
6	PS	Polystyrene foam, cutlery
7	Other	Mixed plastics, harder to recycle

Problems with recycling:

Sorting is labour-intensive and error-prone. Different polymers can't be melted together.
Quality degrades with each recycling cycle. Most plastics can only be recycled 2-5 times before becoming unusable.
Some plastics (PVC, polystyrene, mixed) are difficult or uneconomical to recycle.
Contamination (food residue, labels, mixed materials) reduces value.
Low demand for recycled plastic in some markets.
Current global recycling rate: ~ 9-30% (varies hugely by country).

Most-recycled plastics:

PET (code 1) — high demand for recycled drinks bottles + polyester fibre.
HDPE (code 2) — high demand for new bottles.

Less-recycled:

LDPE (code 4) — plastic bags often go to landfill.
PS (code 6) — polystyrene is hard to recycle economically.
PVC (code 3) — multiple additives + formulations.

Disposal option 4: Litter / oceans.

Plastic that escapes the waste-management system ends up as LITTER — on streets, in rivers, ultimately in OCEANS.

Problems with ocean plastic:

Great Pacific Garbage Patch — a vast accumulation of floating plastic in the North Pacific (~ 80,000 tonnes spread over 1.6 million km²).
Wildlife harm: turtles eat plastic bags (mistaking for jellyfish); seabirds feed plastic to chicks; fish ingest microplastics.
Microplastics — plastic broken into small pieces (< 5 mm) by UV + waves. Found in:
- Oceans (everywhere — even in deep-sea trenches).
- Soils.
- Drinking water (tap and bottled).
- Salt (sea salt and table salt).
- Human bloodstream (recent studies).
- Lungs (inhaled).
Long-term health effects on humans and wildlife: UNCLEAR but concerning.

Solutions — the 3 Rs + innovation.

1. REDUCE — use less plastic.

Avoid single-use plastics (straws, bags, bottles, takeaway).
Refillable containers.
Buy in bulk.
Choose products with minimal packaging.
Government policies:
- Plastic bag charges (UK 10p — reduced bag use by ~ 80%).
- Bans on single-use plastics (EU, many countries).
- Deposit-return schemes for bottles (Germany, Norway — > 95% return rates).

2. REUSE — extend life of plastic.

Reusable water bottles instead of single-use.
Cloth shopping bags.
Glass / metal food containers.
Donate / sell rather than discard.

3. RECYCLE — when plastic must be discarded.

Sort properly by type.
Wash to remove residue.
Support local recycling.
Push for improvements: better collection, extended producer responsibility, chemical recycling.

4. INNOVATE — develop better materials.

Biodegradable plastics: polylactic acid (PLA) from corn starch; polyhydroxyalkanoates (PHA) from bacteria. Compostable in industrial composters.
Plant-based plastics: bio-PET (from sugar cane), bio-polyethene (from bioethanol). Same chemistry but renewable feedstock.
CHEMICAL RECYCLING: technologies to break polymers back to monomers, then re-polymerise. Maintains quality across many cycles.
CIRCULAR ECONOMY: design products for disassembly + recycling from the start. Manufacturers responsible for end-of-life management.

Government + global cooperation.

Various initiatives:

EU Single-Use Plastics Directive (2021) — banned 10 most-littered single-use plastic items.
UN Plastic Pollution Treaty (negotiation ongoing) — global agreement to reduce plastic pollution.
Extended Producer Responsibility (EPR) laws — manufacturers must take back packaging.
Plastic tax (some countries) — adds cost to single-use plastic.

The chemistry behind solutions.

The fundamental problem is that addition polymers have strong, stable C–C backbones with no functional groups for microbial attack. Chemistry-based solutions:

Add functional groups during synthesis to make the polymer biodegradable (e.g. some 'oxo-biodegradable' plastics incorporate carbonyl groups that UV can attack).
Use condensation polymers with ester/amide linkages that can hydrolyse.
Use natural polymers (cellulose, starch, PLA) that microbes can break down.
Improve recycling chemistry to make 'closed-loop' systems where polymers are re-used efficiently.

The bigger picture.

The plastic problem isn't just about disposal — it's about our entire pattern of single-use consumption. The most environmentally responsible polymer is the one NOT MADE in the first place. Reducing demand for plastic packaging is more effective than recycling more.

That said, plastics are extraordinarily useful materials — light, cheap, durable, mouldable, electrically insulating. Replacing them entirely is neither possible nor desirable. The challenge is to use them wisely, manage them well, and develop better alternatives where possible.

Edexcel exam tip.

Common 4CH1 questions:

Why are addition polymers non-biodegradable?
What are the problems with landfill / incineration / recycling?
Suggest ONE strategy for reducing the environmental impact.

Mark scheme answers:

'Strong C–C backbone, no functional groups for microbes to attack'.
'PVC releases HCl on incineration → acid rain'.
'Recycling: must sort by type; quality degrades'.
'Use biodegradable plastics' OR 'recycle' OR 'reduce single-use'.

Use these phrases in your answers.

Addition polymers are NON-BIODEGRADABLE — strong C–C backbone, no functional groups for microbes.
Plastic bags persist for 500-1000 years in landfill.
Disposal options: landfill (poor — permanent waste), incineration (CO₂ + HCl from PVC), recycling (limited).
PVC incineration releases HCl → acid rain (other addition polymers just release CO₂ + H₂O).
Recycling codes 1-7; PET (1) and HDPE (2) widely recycled; PS (6) and mixed (7) less so.
Microplastics now found in oceans, soils, drinking water, salt, blood — long-term effects unclear.
Solutions: REDUCE consumption, REUSE items, RECYCLE properly, INNOVATE (biodegradable plastics, plant-based).
PLA (polylactic acid) from corn starch is biodegradable; bio-PET from sugar cane is renewable.

See the full worked example for polymers →

Quick recap

Polymer = large molecule from many monomer units joined together. Polymerisation = the joining reaction.
TWO types: ADDITION (one alkene monomer, no atoms lost) + CONDENSATION (two monomers, small molecule lost).
Addition examples: ethene → poly(ethene); propene → poly(propene); chloroethene → PVC; tetrafluoroethene → PTFE.
Repeat unit: square brackets [...] with subscript n; C=C of monomer becomes C–C in repeat unit.
Find monomer from repeat unit: close C–C between main-chain carbons back to C=C.
Condensation: two monomers each with 2 functional groups + loss of water per linkage.
Polyester (Terylene/PET): diacid + diol → ester linkages. Used in clothing fibres + drinks bottles.
Polyamide (nylon-6,6): diacid + diamine → amide linkages. Used in ropes, clothing, parachutes.
Addition polymers are NON-BIODEGRADABLE (strong C–C backbone, no functional groups for microbes).
Disposal: landfill (poor), incineration (CO₂ + HCl from PVC → acid rain), recycling (limited).
Solutions: reduce, reuse, recycle; biodegradable plastics (PLA from corn); plant-based polymers.
Natural condensation polymers: proteins (peptide bonds), DNA (phosphodiester), cellulose (glycosidic).

Memorise this

Verbatim phrases and definitions Cambridge mark schemes credit.

Polymer definition: 'a large molecule made of many small repeating units (monomers) joined together'.
Polymerisation: 'the reaction joining many monomers to form a polymer'.
Addition polymerisation equation template: n CH₂=CHR → ─(CH₂–CHR)ₙ─.
Specific: n CH₂=CH₂ → ─(CH₂–CH₂)ₙ─ (poly(ethene)).
Specific: n CH₂=CHCl → ─(CH₂–CHCl)ₙ─ (PVC = poly(chloroethene)).
Specific: n CH₂=CHCH₃ → ─(CH₂–CH(CH₃))ₙ─ (poly(propene)).
Repeat unit must include: square brackets, single C–C bond (not C=C), side groups, subscript n.
Condensation polymerisation: 'TWO monomers, each with TWO functional groups, joining with LOSS of water'.
Polyester equation: n HOOC-X-COOH + n HO-Y-OH → ─(CO-X-COO-Y-O)ₙ─ + 2n H₂O.
Polyamide equation: n HOOC-X-COOH + n H₂N-Y-NH₂ → ─(CO-X-CONH-Y-NH)ₙ─ + 2n H₂O.
Why addition polymers are non-biodegradable: 'strong C–C backbone, no functional groups for microbes / enzymes to attack'.
Why PVC incineration is concerning: 'PVC contains Cl → produces HCl gas on incineration → acid rain'.
Disposal hierarchy (most preferred first): REDUCE → REUSE → RECYCLE → recover energy (incineration) → landfill.

How it’s examined

Polymers appear on every 4CH1 paper, typically worth 6-10 marks per session. Paper 1 (4CH1/1C) items: (a) define polymer/monomer/polymerisation (3 marks); (b) write equation for polymerisation of given alkene (3 marks); (c) draw repeat unit OR identify monomer from repeat unit (3 marks); (d) state uses of common polymers (PE, PP, PVC, PTFE) (2-3 marks); (e) environmental impact / non-biodegradability (4-6 marks). Paper 2 (4CH1/2C) items: deeper analysis including CONDENSATION polymerisation — equation, functional groups, byproduct; polyester / polyamide examples; comparison with addition polymerisation. Common errors: drawing repeat unit with C=C still present (should be C–C); missing brackets/subscript n; condensation equation without the water byproduct; saying 'all plastics' release HCl on burning (only PVC). Mark scheme keywords: 'C=C opens / breaks', 'no atoms lost' (addition); 'water released', 'two different monomers' (condensation); 'non-biodegradable', 'strong C–C backbone'.

Sources: Pearson Edexcel International GCSE Chemistry 4CH1 specification — Issue 4, September 2024 (valid for 2026 onwards); Pearson Edexcel 4CH1 Examiner Reports 2022-2024; 4CH1/1C May/Jun 2024 question paper and mark scheme; 4CH1/1C January 2024 question paper and mark scheme; 4CH1/2C May/Jun 2024 question paper and mark scheme; 4CH1/2C January 2024 question paper and mark scheme. Last reviewed 2026-05-12.

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Step-by-step worked examples — Polymers

Step-by-step solutions to past-paper-style questions on polymers, written exactly the way a tutor would explain them at the board.

1Define key polymer terms and show with poly(ethene) (4 marks, Paper 1)
Core• Adapted from 4CH1/1C May/Jun 2024 Q8• polymer, monomer, spec-4.37, spec-4.38
Question
(a) Define the terms POLYMER, MONOMER, and POLYMERISATION. (b) Write the equation for the polymerisation of ethene (CH₂=CH₂) to poly(ethene). (c) Draw the repeat unit of poly(ethene). (4 marks)
Step-by-step solution
1. Step 1
  (a) Definitions (1 M). • Polymer: a very LARGE molecule made up of MANY small repeating units (monomers) joined together. Typically thousands of monomers per polymer molecule → molecular masses can reach > 100,000. • Monomer: a SMALL molecule that can join with OTHER monomers (of the same type or different) to form a polymer. For addition polymerisation, the monomer is always an ALKENE (has a C=C double bond). • Polymerisation: the chemical REACTION by which monomers join together to form a polymer.
2. Step 2
  (b) Equation (1 A). Ethene (CH₂=CH₂) joins via addition polymerisation:
  $n\,\text{CH}_2{=}\text{CH}_2 \xrightarrow{\text{cat, P, T}} {-}(\text{CH}_2{-}\text{CH}_2)_n{-}$
3. Step 3
  (b) Conditions. Industrial poly(ethene) is made under two main conditions: • LDPE (low-density poly(ethene)): high T (~ 200 °C), very high P (~ 1500 atm), with an organic peroxide initiator. Branched chains → loose packing → soft, flexible plastic. • HDPE (high-density poly(ethene)): lower T (~ 50-80 °C), lower P (~ 10 atm), with a Ziegler-Natta or metallocene catalyst. Linear chains → tight packing → harder, denser plastic.
4. Step 4
  (c) Repeat unit (1 A). The repeat unit is ONE monomer's worth of the chain, with the C=C double bond now a C–C single bond. Drawn in square brackets with subscript n to indicate 'this unit repeats many times'.
  
  ┌── ──┐ | H H | | | | | ─C ─ C─ | | | | | H H | └── ──┘ ₙ
  
  Or written linearly as: ─(CH₂–CH₂)ₙ─. The brackets mark the boundaries of the repeat unit; the n means 'this unit is repeated thousands of times'.
5. Step 5
  (c) Key features of the repeat unit (1 B). Notice: • The C=C of the monomer has OPENED → became a C–C single bond. • The unit looks like the monomer with the double bond replaced by a single bond, and with bonds extending from each end of the unit (to join to the next unit). • 'n' is typically 1000-10000 for typical poly(ethene) — but only the basic unit is drawn. • NO atoms are lost — both H atoms and both C atoms of the monomer are in the repeat unit.
Answer
(a) Polymer = large molecule made of many monomer units joined together. Monomer = small molecule that joins to form a polymer. Polymerisation = the reaction joining monomers. (b) n CH₂=CH₂ → ─(CH₂–CH₂)ₙ─. (c) Repeat unit: ─(CH₂–CH₂)ₙ─ in square brackets with subscript n.
Examiner tip
Edexcel 4-mark mark scheme: 1 for polymer definition; 1 for monomer definition; 1 for equation with n on both sides; 1 for repeat unit clearly drawn with brackets, single C–C bond, and subscript n. Common error: drawing the repeat unit with C=C (forgetting that polymerisation breaks the double bond) or missing the brackets / subscript n.
2PVC from chloroethene — equation and uses (4 marks, Paper 1)
Core• Adapted from 4CH1/1C Jan 2024 Q6• PVC, addition polymerisation, spec-4.38
Question
PVC (poly(chloroethene)) is made from chloroethene (CH₂=CHCl), also called vinyl chloride. (a) Write the equation for the polymerisation. (b) Draw the repeat unit of PVC. (c) State THREE common uses of PVC. (d) State ONE environmental concern with the disposal of PVC. (4 marks)
Step-by-step solution
1. Step 1
  (a) Equation (1 M). Many chloroethene monomers polymerise via addition (no loss of atoms):
  $n\,\text{CH}_2{=}\text{CHCl} \rightarrow {-}(\text{CH}_2{-}\text{CHCl})_n{-}$
2. Step 2
  (b) Repeat unit (1 A).
  
  ┌── ──┐ | H H | | | | | ─C ─ C ─ | | | | | H Cl | └── ──┘ ₙ
  
  Linearly: ─(CH₂–CHCl)ₙ─. The Cl atom is retained on every other carbon (every monomer brings one Cl). The C=C of the monomer becomes C–C in the polymer.
3. Step 3
  (c) Three uses of PVC (1 A). • Pipes for water supply and drainage (PVC is rigid and durable when made without plasticisers). • Window frames (UPVC — un-plasticised PVC; cheap, weather-resistant alternative to wood). • Electrical cable insulation (PVC is a good electrical insulator; can be made flexible with plasticisers). • Flooring (vinyl floor tiles). • Vinyl records (the original use). • Clothing / leather substitute (flexible PVC made with phthalate plasticisers).
4. Step 4
  (d) Environmental concern (1 B). PVC contains CHLORINE atoms. When PVC is INCINERATED (burnt at landfill or incinerator), it can release HYDROGEN CHLORIDE GAS (HCl) — an acidic, toxic, corrosive gas that contributes to ACID RAIN. Other concerns: • Like most addition polymers, PVC is NON-BIODEGRADABLE → persists in landfill. • Phthalate plasticisers (used to make PVC flexible) can leach out → endocrine disruptors. • Recycling is difficult — different PVC formulations and additives prevent simple melt-and-reform.
Answer
(a) n CH₂=CHCl → ─(CH₂–CHCl)ₙ─. (b) Repeat unit: square brackets containing –CH₂–CHCl– with subscript n. (c) Pipes, window frames, electrical cable insulation, flooring (any three). (d) Releases HCl gas if incinerated → acid rain; non-biodegradable.
Examiner tip
Edexcel 4-mark mark scheme: 1 for balanced equation with n; 1 for repeat unit clearly showing Cl on every other C; 1 for three valid uses; 1 for environmental concern (HCl from incineration is the standout). Common error: drawing the repeat unit as ─(CH₂=CHCl)ₙ─ with the double bond — polymerisation breaks the C=C.
3Identify the monomer from the repeat unit (3 marks, Paper 1)
Core• Adapted from 4CH1/1C May/Jun 2024 Q7• monomer, repeat unit, spec-4.39
Question
A polymer has the repeat unit ─(CH₂–CHCH₃)ₙ─. (a) Identify the monomer that produces this polymer. (b) Write the equation for the polymerisation. (c) Name the polymer and state ONE common use. (3 marks)
Step-by-step solution
1. Step 1
  (a) Find the monomer (1 M). To identify the monomer from a repeat unit:
  
  Take ONE repeat unit.
  
  CLOSE THE BOND between the two carbons that connect to neighbouring units → restore the C=C double bond.
  
  The result is the monomer.
  
  For ─(CH₂–CHCH₃)ₙ─: • Repeat unit: –CH₂–CHCH₃–. • Close the C–C between the two main-chain carbons to make C=C: CH₂=CH–CH₃.
  
  Monomer: CH₂=CHCH₃ = propene (also written CH₃CH=CH₂).
2. Step 2
  (b) Polymerisation equation (1 A).
  $n\,\text{CH}_2{=}\text{CH}\text{CH}_3 \rightarrow {-}(\text{CH}_2{-}\text{CH}(\text{CH}_3))_n{-}$
3. Step 3
  (c) Polymer name + use (1 A). Poly(propene) — also called polypropylene or polypropene. Uses include: • Plastic containers (food packaging, yoghurt pots, takeaway containers). • Ropes and synthetic fibres (carpets, twine). • Plastic chairs and crates (rigid, low-cost, durable). • Car parts (bumpers, interior components — light and tough).
  
  (Pick any one for the mark.)
Answer
(a) Propene (CH₂=CHCH₃ or CH₃CH=CH₂). (b) n CH₂=CHCH₃ → ─(CH₂–CH(CH₃))ₙ─. (c) Poly(propene). Use: plastic containers / ropes / fibres.
Examiner tip
Edexcel 3-mark mark scheme: 1 for identifying monomer = propene; 1 for polymerisation equation; 1 for naming the polymer + a valid use. Mark scheme keyword: 'close the bond between adjacent repeat units to restore the C=C'.
4Condensation polymerisation — polyester (5 marks, Paper 2)
Higher• Adapted from 4CH1/2C May/Jun 2024 Q9• condensation, polyester, spec-4.42P, spec-4.43P
Question
Polyesters such as Terylene are made by condensation polymerisation. (a) Define 'condensation polymerisation'. (b) Identify the TWO functional groups that the monomers must contain. (c) Show how a generic polyester is formed from a dicarboxylic acid (HOOC-X-COOH) and a diol (HO-Y-OH). Include the equation and the small molecule released. (d) State TWO uses of Terylene. (5 marks)
Step-by-step solution
1. Step 1
  (a) Definition (1 M). Condensation polymerisation: a type of polymerisation in which TWO different monomers, each having TWO FUNCTIONAL GROUPS at the ends of the molecule, join together with the loss of a SMALL MOLECULE (usually water, sometimes HCl). The 'condensation' refers to the elimination of the small molecule each time a bond forms.
2. Step 2
  (b) Functional groups (1 A). For a polyester: • Monomer 1: DIcarboxylic acid — has TWO carboxyl groups (–COOH), one at each end. Example: hexanedioic acid HOOC–(CH₂)₄–COOH. • Monomer 2: DIol — has TWO hydroxyl groups (–OH), one at each end. Example: ethane-1,2-diol HO–CH₂–CH₂–OH (glycol).
  
  The TWO functional groups per monomer are essential — they allow each monomer to react with TWO neighbours (one on each end) → growing chain. A monomer with only one functional group would react once and stop, giving small molecules, not a polymer.
3. Step 3
  (c) Generic polyester equation (1 A). Each diacid joins to two diols by forming TWO ester linkages → releasing TWO water molecules per acid molecule.
  
  For n diacid + n diol → polyester + 2n × H₂O:
  $n\,\text{HOOC-X-COOH} + n\,\text{HO-Y-OH} \rightarrow {-}(\text{CO-X-COO-Y-O})_n{-} + 2n\,\text{H}_2\text{O}$
4. Step 4
  (c) How the linkage forms (1 B). Each ester linkage –COO– forms when: • –COOH of the acid + HO– of the alcohol • → loss of H₂O • → leaving –CO–O– between the two carbon chains.
  
  In a polyester chain, alternating –CO–O–Y–O–CO– segments connect the diacid and diol units. Many ester linkages per polymer chain (one between each pair of monomer units → 2n linkages per n diacid + n diol). The same many-water-molecules-lost feature is what makes this 'condensation polymerisation'.
5. Step 5
  (d) Uses of Terylene (1 B). Terylene (also called Dacron in USA; PET = poly(ethylene terephthalate) is the same chemical): • Clothing fibres (synthetic fabric — durable, easy-care, wrinkle-resistant; mixed with cotton in shirts, suits). • PET drinks bottles (clear, lightweight, shatter-resistant — used for water, fizzy drinks, juice). • Photographic film base (Mylar). • Conveyor belts and reinforcement fibres (high tensile strength). • Sails for yachts (lightweight, strong, doesn't stretch).
  
  (Pick any two for the mark.)
Answer
(a) Condensation polymerisation: two different monomers (each with 2 functional groups) join with loss of small molecule (H₂O). (b) Diacid (–COOH at each end) + diol (–OH at each end). (c) n HOOC-X-COOH + n HO-Y-OH → ─(CO-X-COO-Y-O)ₙ─ + 2n H₂O. (d) Uses of Terylene: clothing fibres + PET drinks bottles.
Examiner tip
Edexcel 5-mark mark scheme: 1 for definition (two monomers + small molecule lost); 1 for naming the two functional groups (–COOH + –OH); 1 for equation with water lost; 1 for showing both ester linkages per repeat; 1 for two uses. Mark-scheme keyword: 'condensation' + 'loss of water'.

5Compare addition vs condensation polymerisation (5 marks, Paper 2)

Higher• Adapted from 4CH1/2C Jan 2024 Q8• comparison, addition, condensation, spec-4.43P

Question

Compare addition polymerisation and condensation polymerisation. Discuss: (a) the number and type of monomers, (b) what happens to the monomer functional groups, (c) byproducts of the reaction, (d) one example polymer of each type. (5 marks)

Step-by-step solution

Step 1
(a) Number and type of monomers (1 M). • Addition: ONE type of monomer. The monomer is an ALKENE — must contain a C=C double bond. Examples: ethene, propene, chloroethene. • Condensation: TWO different monomers. Each monomer has TWO functional groups (one at each end). Examples: diacid + diol → polyester; diacid + diamine → polyamide.
Step 2
(b) Functional groups during reaction (1 A). • Addition: the C=C double bond OPENS up; each carbon gains a bond to the adjacent monomer. No functional groups are 'lost'; everything stays in the polymer. • Condensation: the two reacting functional groups (e.g. –COOH and –OH) JOIN to form a new linkage (e.g. ester –COO–), with the elimination of a small molecule (e.g. H₂O — from the –OH and –OH or –NH and –OH).
Step 3
(c) Byproducts (1 A). • Addition: NO byproduct. Every atom of every monomer ends up in the polymer. • Condensation: A SMALL MOLECULE is eliminated per linkage formed. Usually WATER (H₂O) for polyesters and polyamides. Can be HCl for some polyamides made from acid chlorides. So a polyester from n diacid + n diol has 2n water molecules eliminated.

Step 4

(d) Examples (1 A).

Type	Example polymer	Monomer(s)	Use
Addition	Poly(ethene)	Ethene (CH₂=CH₂)	Plastic bags, bottles
Addition	Poly(propene)	Propene	Containers, fibres
Addition	PVC = poly(chloroethene)	Chloroethene (CH₂=CHCl)	Pipes, window frames
Condensation	Terylene / PET	Diacid + diol	Clothing, drinks bottles
Condensation	Nylon-6,6	Diacid + diamine	Clothing, ropes, parachutes

Step 5

(e) Summary comparison (1 B).

Feature	Addition	Condensation
Monomer type	Alkene (with C=C)	Two monomers, each with 2 functional groups
Number of monomer types	ONE	TWO
Functional groups	C=C opens up	–OH + –COOH, or –NH₂ + –COOH
Byproduct	NONE	H₂O (or HCl)
Mechanism	Free radicals / catalyst opens C=C	Each linkage eliminates a small molecule
Bond formed	C–C	Ester (–COO–) or amide (–CONH–)
Examples	Poly(ethene), PVC, polystyrene	Terylene, nylon, proteins, DNA
Naturally occurring?	Rarely	YES — proteins, DNA, cellulose are all condensation polymers

Answer

(a) Addition: ONE monomer type (alkene). Condensation: TWO monomers (each with 2 functional groups). (b) Addition: C=C opens. Condensation: functional groups combine with loss of small molecule. (c) Addition: NO byproduct. Condensation: H₂O (or HCl) per linkage. (d) Addition: poly(ethene) from ethene. Condensation: Terylene from diacid + diol.

Examiner tip

Edexcel 5-mark mark scheme: 1 for # monomers; 1 for functional groups behavior; 1 for byproduct; 1 for naming examples of each; 1 for clear comparison structure. Mark scheme keywords: 'C=C opens up', 'loss of water / small molecule'.

Model Answers — Polymers

High-scoring sample answers for polymers on the Pearson Edexcel IGCSE 4CH1 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question

4CH1/1C-style — addition polymerisation5 marks

Explain what is meant by addition polymerisation. Use the formation of poly(ethene) from ethene as an example. Include the equation, the repeat unit, the conditions, and explain why the reaction is described as 'addition'. (5 marks)

Model answer

Definition of addition polymerisation.

Addition polymerisation is a reaction in which many small unsaturated molecules (MONOMERS, with a C=C double bond) join together to form a single very long molecule (POLYMER) — with NO atoms lost during the joining. Every atom of every monomer ends up in the polymer chain.

The 'addition' name reflects the fact that, like a simple alkene + bromine addition reaction, the C=C double bond OPENS UP (one bond of the C=C 'opens') and is used to form new bonds to neighbouring monomer molecules. No HCl, no H₂O, no atoms 'expelled' — pure joining.

The monomer: ethene.

Ethene (CH₂=CH₂) is the simplest alkene. Its structure:

The C=C double bond is the key feature — its breaking is what enables polymerisation.

The polymerisation reaction.

When many ethene molecules are forced together under the right conditions, each C=C opens and the resulting carbon atoms form bonds to carbon atoms of neighbouring ethene molecules:

$n\,\text{CH}_2{=}\text{CH}_2 \rightarrow {-}(\text{CH}_2{-}\text{CH}_2){-}_n$

The polymer formed is poly(ethene) (also called polythene, polyethylene, PE). 'n' is typically 1000-100,000, giving polymer molecules with molecular masses from ~ 30,000 to ~ 3,000,000.

The repeat unit.

The repeat unit is the segment of the polymer that repeats — the part inside the square brackets:

  ┌──        ──┐
  |   H   H   |
  |   |   |   |
  ─C ─ C─
  |   |   |   |
  |   H   H   |
  └──        ──┘ ₙ

Or linearly: ─(CH₂–CH₂)ₙ─.

Key points about the repeat unit:

It contains exactly the same atoms as ONE monomer (2 C, 4 H).
The double bond C=C has become a single bond C–C.
The two bonds extending from each end of the unit connect to neighbouring units.
The 'n' indicates 'this unit repeats n times'.

Why the reaction is 'addition'.

The C=C double bond consists of two bonds (one σ + one π — see Topic 4.4 alkenes). During polymerisation:

The π bond BREAKS (it's weaker — about 264 kJ/mol).
Each carbon atom of the former double bond now has a free 'bonding position'.
These positions are FILLED by bonding to adjacent monomer molecules (one to each side).
The σ bond is retained.

In the polymer, the C=C double bond has become a C–C single bond AND two new C–C bonds have formed to neighbouring monomers. Net result: TWO new bonds per monomer (one to each side, joining to neighbours). No atoms expelled. This is the 'addition' principle.

Compare with condensation polymerisation: when two monomers join in a condensation, a small molecule (usually water) is ELIMINATED. In addition, NOTHING is eliminated → name 'addition'.

Industrial conditions.

Industrial poly(ethene) is made under TWO main sets of conditions, giving two distinct products:

LDPE (low-density poly(ethene)):

Conditions: HIGH temperature (~ 200 °C), VERY HIGH pressure (~ 1500-2000 atm), organic peroxide initiator (free radical mechanism).
Result: BRANCHED chains. The branches prevent close packing → low density (~ 0.92 g/cm³) → SOFT, FLEXIBLE plastic.
Uses: plastic bags, cling film, squeezy bottles, food wrap.

HDPE (high-density poly(ethene)):

Conditions: LOWER temperature (~ 50-80 °C), LOWER pressure (~ 1-10 atm), Ziegler-Natta catalyst (titanium chloride + aluminium alkyl).
Result: STRAIGHT, LINEAR chains. They pack tightly → higher density (~ 0.95 g/cm³) → HARDER, STRONGER plastic.
Uses: milk jugs, detergent bottles, water pipes, plastic crates, durable bags.

The conditions matter for the PROPERTIES of the polymer — but for 4CH1, the basic equation $n\,\text{CH}_2{=}\text{CH}_2 \rightarrow {-}(\text{CH}_2{-}\text{CH}_2){-}_n$ is the key takeaway.

Free radical mechanism (deeper insight, beyond 4CH1).

In LDPE production:

An organic peroxide initiator breaks into two free radicals: R–O–O–R → 2 R–O•.
The radical attacks an ethene molecule: R–O• + CH₂=CH₂ → R–O–CH₂–CH₂•.
The new radical attacks another ethene: R–O–CH₂–CH₂• + CH₂=CH₂ → R–O–CH₂–CH₂–CH₂–CH₂•.
Each step adds a CH₂–CH₂ unit. The radical 'walks' down the chain → grows the polymer.
Termination: two growing chains meet end-to-end → join → kill the radicals.
Branching: occasionally the radical reaches back into the chain → side branch.

This is why high T and P give branched LDPE: high radical activity at high T causes random branching.

Other addition polymers.

Many alkene monomers form addition polymers analogously:

Monomer	Polymer	Use
CH₂=CH₂ (ethene)	Poly(ethene)	Bags, bottles, films
CH₂=CHCH₃ (propene)	Poly(propene)	Containers, fibres
CH₂=CHCl (chloroethene = vinyl chloride)	PVC = poly(chloroethene)	Pipes, frames
CF₂=CF₂ (tetrafluoroethene)	PTFE (Teflon)	Non-stick coatings
CH₂=CHC₆H₅ (styrene)	Polystyrene	Insulation, packaging
CH₂=CHC(CH₃)=CHCH₂... etc.	Various others	Various plastics

All follow the same basic pattern: alkene → addition polymer with single C–C bonds in place of the original C=C.

Summary.

Feature	Detail
Type of monomer	Alkene (must have C=C)
Bond that breaks	The π bond of C=C
New bonds formed	Two new C–C bonds per monomer (one to each neighbour)
Atoms lost	NONE — addition is 'atom-economic'
Equation	n CH₂=CH₂ → ─(CH₂-CH₂)ₙ─
Product	A long-chain plastic
Industrial conditions	LDPE: high T + P, peroxide. HDPE: lower T + P, catalyst

This is the chemistry underpinning the entire plastics industry. Without addition polymerisation, there would be no plastic bags, no cling film, no PVC pipes, no insulated electrical cables, no Teflon — modern life depends on this single reaction.

Why this scores

Edexcel 5-mark mark scheme: 1 for definition (many monomers join with no loss of atoms); 1 for ethene + C=C double bond as monomer; 1 for balanced equation; 1 for repeat unit drawn with brackets + n; 1 for explaining 'addition' (no atoms lost / C=C opens up).

Question

4CH1/2C-style — condensation polymerisation5 marks

Describe condensation polymerisation. Use polyester (Terylene) as an example. Include the functional groups required on the monomers, the equation showing the formation of the polymer, and the small molecule that is eliminated. Compare with addition polymerisation. (5 marks)

Model answer

Definition of condensation polymerisation.

Condensation polymerisation is a type of polymerisation in which TWO DIFFERENT monomers, each with TWO functional groups (one at each end of the molecule), join together with the LOSS OF A SMALL MOLECULE (usually water) at each linkage. Many monomers join in this way to form a long polymer chain.

The 'condensation' refers to the elimination of the small molecule (analogous to the condensation reaction in organic chemistry, e.g. ester formation).

Functional groups required.

For each linkage, one functional group on monomer 1 reacts with one functional group on monomer 2. So each monomer must have TWO functional groups (one at each end) — that way both ends can react and the chain can grow.

For a POLYESTER (e.g. Terylene):

Monomer	Functional groups	Example
Dicarboxylic acid	TWO carboxyl groups (–COOH at each end)	Benzene-1,4-dicarboxylic acid (terephthalic acid) HOOC-C₆H₄-COOH
Diol	TWO hydroxyl groups (–OH at each end)	Ethane-1,2-diol (ethylene glycol) HO-CH₂-CH₂-OH

The –COOH of the acid reacts with the –OH of the alcohol → forms an ester linkage (–COO–) + water. Each monomer can do this on BOTH ends → chain grows in both directions.

For a POLYAMIDE (e.g. nylon-6,6):

Monomer	Functional groups	Example
Dicarboxylic acid	TWO –COOH	Hexanedioic acid HOOC-(CH₂)₄-COOH
Diamine	TWO –NH₂ groups	Hexane-1,6-diamine H₂N-(CH₂)₆-NH₂

The –COOH + –NH₂ → amide linkage (–CO–NH–) + water.

The polyester (Terylene) equation.

Generic equation showing repeat unit and water loss:

$n\,\text{HOOC-X-COOH} + n\,\text{HO-Y-OH} \rightarrow {-}(\text{CO-X-COO-Y-O})_n{-} + 2n\,\text{H}_2\text{O}$

(where X and Y are the carbon backbones of the diacid and diol).

For Terylene specifically:

$n\,\text{HOOC-C}_6\text{H}_4\text{-COOH} + n\,\text{HO-CH}_2\text{CH}_2\text{-OH} \rightarrow {-}(\text{CO-C}_6\text{H}_4\text{-COO-CH}_2\text{CH}_2\text{-O})_n{-} + 2n\,\text{H}_2\text{O}$

The polymer repeat unit:

─CO–C₆H₄–COO–CH₂CH₂–O─    (repeats n times)
  └──── acid half ────┘   └─ alcohol half ─┘

Each repeat unit contains TWO ester linkages — one between the acid and the diol on each side.

Water — the eliminated small molecule.

In each ester linkage formation:

The H of the –COOH carboxyl + the OH of the diol alcohol → H₂O.
The remaining –CO– of the acid joins to the –O– of the alcohol → ester linkage –COO–.

For 1 acid + 1 alcohol = 1 ester linkage = 1 water. For a chain of n diacid + n diol = 2n ester linkages = 2n water molecules eliminated.

Diagram of the linkage formation.

HOOC-X-CO-OH + H-O-Y-OH → HOOC-X-CO-O-Y-OH + H₂O

  acid half        alcohol half        new ester linkage

Repeated on the other end of each monomer → growing chain.

Comparison with addition polymerisation.

Feature	Addition	Condensation
Number of monomer types	ONE (alkene)	TWO (each with 2 functional groups)
Functional groups in monomer	C=C double bond	–COOH + –OH (polyester) or –COOH + –NH₂ (polyamide)
What happens at C=C	Opens up to single bond	n/a (different chemistry)
Byproduct	NONE	Water (one per linkage)
Atom economy	100%	< 100% (atoms lost as water)
Mechanism	Free radicals / catalyst opens C=C	Each linkage eliminates H₂O
Bond in polymer backbone	All C–C single bonds	Ester –COO– or amide –CONH– linkages alternating with C–C chains
Examples	Poly(ethene), PVC, polystyrene, PTFE	Terylene, nylon, proteins, DNA, polyester clothing
Naturally occurring?	Rarely (a few microbial products)	YES — proteins, DNA, cellulose are all condensation polymers
Biodegradability	Usually NOT biodegradable	Often more biodegradable (ester/amide bonds can hydrolyse)

Why condensation polymers can be more environmentally friendly.

The ester (–COO–) and amide (–CONH–) bonds in condensation polymers can be HYDROLYSED back to the original monomers by water, acid, or alkali — i.e. they can be 'broken back down' under the right conditions. This means:

Some condensation polymers are biodegradable (microorganisms can hydrolyse them).
Recycling is more feasible (chemical hydrolysis can reclaim the monomers).
Biological polymers (proteins, DNA) are inherently recyclable in nature.

Addition polymers have all-C–C backbones, which are very stable and difficult to break down → persist in landfills and oceans.

Uses of polyester (Terylene / PET).

Clothing fibre: Terylene is used in shirts, suits, trousers (often blended with cotton); durable, easy-care, wrinkle-resistant.
Drinks bottles (PET): clear, lightweight, shatter-resistant — used for water, fizzy drinks, juice. Recycling code 1.
Photographic film: Mylar (a polyester film).
Sails and ropes: high tensile strength, doesn't stretch.
Conveyor belts: heavy-duty reinforcement.

Natural condensation polymers — bonus context.

The same chemistry that makes Terylene also makes proteins (amino acids condensing with loss of water to form peptide bonds, which are amides) and DNA (nucleotides condensing with loss of water to form phosphodiester bonds). Cellulose (the main component of plant cell walls) is a condensation polymer of glucose units linked by glycosidic bonds (with loss of water). So condensation polymerisation is one of the most important reactions in biology AND chemistry.

Summary.

Condensation polymerisation = two monomers (each with 2 functional groups) join with loss of a small molecule (water) per linkage. Many monomers join → polymer + many water molecules. Terylene from terephthalic acid + ethylene glycol is the classic 4CH1 example.

It contrasts with addition polymerisation, which uses ONE alkene monomer and gives NO byproduct. Condensation gives ester (–COO–) or amide (–CONH–) backbones; addition gives all-C–C backbones.

The differences in chemistry lead to different properties: condensation polymers are more variable in structure (can use many different monomer combinations), can be biodegradable, and dominate the synthetic-fibre industry (clothing). Addition polymers are mostly tough, non-biodegradable plastics for packaging.

Why this scores

Edexcel 5-mark mark scheme: 1 for definition (two monomers + small molecule lost); 1 for naming –COOH + –OH as functional groups; 1 for balanced equation with H₂O eliminated; 1 for showing both linkages in the repeat unit; 1 for comparison with addition (no byproduct vs water byproduct). Mark scheme keyword: 'water eliminated' or 'small molecule eliminated'.

Question

4CH1/1C-style — monomer identification3 marks

A polymer has the repeat unit ─(CHCl–CH₂)ₙ─. Identify the monomer that produced this polymer. Show your reasoning and write the equation for the polymerisation. State the common name and ONE use of this polymer. (3 marks)

Model answer

Identifying the monomer — step-by-step.

The repeat unit is given: ─(CHCl–CH₂)ₙ─. To find the monomer, we work backwards through the polymerisation:

Step 1: Look at ONE repeat unit.

The repeat unit shown is: –CHCl–CH₂–. The two main-chain carbons (CHCl and CH₂) come from ONE monomer (because addition polymerisation joins two carbons of one alkene end-to-end → both carbons retained in the unit).

Step 2: Close the bond between the two main-chain carbons to restore the C=C double bond.

When polymerisation occurred, the C=C of the monomer OPENED → became a C–C single bond. To reverse this, mentally CLOSE the C–C bond back to a C=C.

So –CHCl–CH₂– becomes CHCl=CH₂ (with the double bond restored).

Step 3: Verify by counting atoms.

The original monomer should have: 2 C, 1 Cl, 3 H (these are all the atoms in the repeat unit). Check the monomer CHCl=CH₂: 2 C ✓, 1 Cl ✓, 3 H ✓ (one H on the CHCl carbon, two H on the CH₂ carbon). Good.

The monomer is: chloroethene (CH₂=CHCl), also called vinyl chloride.

(Note: CHCl=CH₂ and CH₂=CHCl are the same molecule — just written different ways round. Convention writes the simpler end first.)

Polymerisation equation.

The forward reaction is addition polymerisation: n chloroethene → polymer.

$n\,\text{CH}_2{=}\text{CHCl} \rightarrow {-}(\text{CH}_2{-}\text{CHCl})_n{-}$

Or in displayed form:

       H       H         ┌──         ──┐
       |       |         |   H     H   |
   n × C   =   C    →    |   |     |   |
       |       |         |  ─C ─── C─  |
       H      Cl         |   |     |   |
                         |   H    Cl   |
                         └──         ──┘ ₙ

The C=C of each chloroethene opens and forms two C–C bonds to neighbouring chloroethene molecules → long polymer chain. NO atoms are lost — addition polymerisation.

Polymer name and use.

The polymer is POLY(CHLOROETHENE), more commonly known as PVC (PolyVinyl Chloride — the older common name based on the old name 'vinyl chloride' for chloroethene). PVC is one of the world's most-used plastics.

Uses of PVC:

Pipes for plumbing, drainage, and electrical conduits (rigid PVC, uPVC).
Window frames (uPVC — unplasticised PVC; durable, weather-resistant, cheap alternative to wood).
Electrical cable insulation (PVC is a good insulator and is flexible when made with plasticisers).
Flooring (vinyl floor tiles, especially in commercial buildings).
Records (the original use — vinyl records).
Imitation leather (flexible PVC made with phthalate plasticisers — used in upholstery, clothing).
Bottles for cooking oil, fruit juice (clear, food-safe formulations).
Medical equipment (IV bags, tubing — but phthalate concerns are reducing this).

(Pick any one for the mark.)

Why PVC has all these uses.

The presence of the Cl atom in the repeat unit gives PVC two key properties:

High density and rigidity (compared with poly(ethene)) → can be moulded into pipes, frames, etc.
Self-extinguishing / flame retardant to some extent (Cl interferes with combustion) → safer than some other plastics for electrical/building applications.

Phthalate PLASTICISERS (large ester molecules) can be added to soften PVC for flexible applications (cable insulation, vinyl flooring, clothing).

Environmental note.

Like most addition polymers, PVC is NON-BIODEGRADABLE and accumulates in landfills + oceans. INCINERATION of PVC releases HYDROGEN CHLORIDE (HCl) gas — acidic and corrosive, contributes to acid rain unless scrubbed by modern incinerators. RECYCLING of PVC is possible but limited by the wide range of formulations and additives. Choice between PVC and alternatives (e.g. polyethene, glass) involves weighing performance against environmental cost.

Final summary.

Item	Detail
Repeat unit	─(CH₂–CHCl)ₙ─
Monomer	Chloroethene CH₂=CHCl (vinyl chloride)
Polymerisation	n CH₂=CHCl → ─(CH₂–CHCl)ₙ─
Polymer name	PVC = poly(chloroethene)
One use	Pipes, window frames, electrical cable insulation (any one)
Method to identify monomer	Close the C–C between repeat units → restore C=C

Why this scores

Edexcel 3-mark mark scheme: 1 for identifying monomer = chloroethene CH₂=CHCl; 1 for writing the polymerisation equation; 1 for naming polymer as PVC + one valid use. Common error: drawing the monomer with the Cl in the wrong position OR forgetting to close the C=C double bond when identifying the monomer.

Question
4CH1/2C-style — environmental impact6 marks
Discuss the environmental issues associated with the disposal of poly(ethene) and similar addition polymers. In your answer, refer to landfill, incineration, and recycling; explain why these polymers persist in the environment; and suggest one strategy for reducing the environmental impact. (6 marks)
Model answer
Why poly(ethene) and similar plastics persist in the environment.

Addition polymers like poly(ethene), poly(propene), PVC, and PTFE are made of long carbon-carbon chains with strong C–C and C–H bonds. They have NO functional groups that bacteria or fungi can easily attack — there are no ester linkages, amide bonds, or other 'cleavable' bonds.

As a result:

Microorganisms cannot break them down. No enzymes exist (or only very slow-acting ones) to hydrolyse C–C bonds in polymer chains.

Sunlight (UV) breaks them down only slowly — UV photolysis can crack the chains over years or decades, but the resulting smaller pieces remain non-biodegradable.

Chemical degradation is minimal at normal environmental T and pH.

Result: plastics can persist for HUNDREDS OF YEARS in the environment (estimated 500-1000 years for a plastic bottle in landfill).

Disposal option 1: Landfill.

Most plastic waste goes to LANDFILL — buried in large pits, often covered with soil.

Problems with landfill:

Plastics take up SPACE that could be used for other purposes (recreation, agriculture, building).

Plastics don't decompose → landfill capacity is permanently lost.

Toxic additives (plasticisers, flame retardants, pigments) can LEACH into groundwater over time → contaminate drinking water.

Microplastics may eventually escape and pollute soils + waterways.

Landfill sites can become 'plastic mountains' that look ugly and devalue surrounding land.

Methane from organic decomposition is released alongside non-decomposing plastic.

Disposal option 2: Incineration (burning).

Some plastic waste is INCINERATED in waste-to-energy plants. The heat is used to generate electricity.

Advantages:

Reduces VOLUME of waste (95-99% reduction in mass).

Generates ENERGY (electricity / heat) — partial offset of fossil fuel use.

Avoids landfill problems.

Problems with incineration:

Burns plastic → produces CO₂ (greenhouse gas) → contributes to climate change.

PVC produces TOXIC GASES: HCl (hydrogen chloride — acidic, corrosive, causes acid rain) and possibly DIOXINS (highly toxic organic pollutants). Modern incinerators have scrubbers to remove HCl, but not all are equipped.

Polystyrene + other polymers can produce styrene + toxic monomers.

Particulate matter from incineration → air pollution.

Some plasticisers + additives are released into the environment as gases.

High capital cost for clean modern incinerators.

So while incineration is a useful disposal option, it must be done in modern, well-designed plants with proper emissions controls.

Disposal option 3: Recycling.

Some plastics CAN be recycled — sorted by type, washed, ground into pellets, and re-moulded.

The recycling code 1-7 system identifies the polymer:

1 = PET (drinks bottles, polyester clothing).

2 = HDPE (milk jugs, detergent bottles).

3 = PVC (pipes, window frames).

4 = LDPE (plastic bags, films).

5 = PP (containers, fibres).

6 = PS (polystyrene foam).

7 = Other (mixed, less commonly recycled).

Problems with recycling:

Plastics MUST BE SORTED carefully — different polymers can't be melted together.

Recycled plastic is often of LOWER QUALITY than fresh polymer (some degradation each cycle).

Limited number of recycling cycles (typically 2-5 before the polymer becomes useless).

Some plastics (e.g. PVC, polystyrene, mixed plastics) are difficult or uneconomical to recycle.

Cleaning and sorting is labour-intensive → high cost.

Not all countries have effective collection systems.

Currently, only ~ 9-30% of plastic waste worldwide is recycled (varies by country).

Disposal option 4: Litter / oceans.

Plastics that are not collected end up as LITTER — on streets, in rivers, eventually washing into the OCEANS.

Problems with ocean plastic:

The Great Pacific Garbage Patch — a vast area of floating plastic in the North Pacific.

Microplastics — plastic broken into small pieces by UV + waves. Now found in oceans, soils, rivers, drinking water, table salt, and even in human bodies. Long-term health effects unknown.

Wildlife harm: turtles eat plastic bags (mistaking for jellyfish), seabirds feed plastic to chicks, fish ingest microplastics → bioaccumulate up the food chain.

Plastic does NOT biodegrade in the ocean — it just breaks into smaller pieces.

Strategy: Reduce, Reuse, Recycle (and innovate).

The most effective strategies, in order of preference:

1. REDUCE — use less plastic in the first place.

Avoid single-use plastics (straws, bags, bottles, packaging).

Use refillable containers.

Buy in bulk.

Choose products with minimal packaging.

Government policies: plastic bag charges (e.g. UK 10p), bans on single-use plastics, deposit-return schemes for bottles.

2. REUSE — extend the life of plastic items.

Reusable water bottles instead of single-use.

Cloth shopping bags.

Reuse plastic containers for storage.

Donate / sell rather than discard.

3. RECYCLE — when plastics must be discarded.

Sort properly by type (use the recycling code).

Wash to remove food residue.

Support local recycling programmes.

Push for improvements: extended producer responsibility, better collection systems.

4. INNOVATE — develop better materials.

Biodegradable plastics (e.g. polylactic acid PLA from corn starch — biodegrades in industrial composters). However: 'biodegradable' is often misleading; many require specific conditions to break down.

Compostable plastics for short-life applications (food packaging that ends up in compost).

Plant-based polymers that replace fossil-fuel-derived plastics.

Chemical recycling: technologies to break polymers back into monomers, then re-polymerise.

Government policy + global cooperation.

Many countries have introduced:

Single-use plastic bans (EU, India, Kenya, others).

Plastic taxes and levies.

Deposit-return schemes (DRS — pay deposit on bottles, get money back when returned).

Extended Producer Responsibility (EPR) — manufacturers must take back their packaging.

International agreements (UN Plastic Treaty in negotiation) aim to coordinate global response — recognising that plastic pollution doesn't respect national borders.

The bigger picture.

The 'plastic problem' isn't just about disposal — it's about our entire pattern of single-use consumption. The most environmentally responsible polymer is the one NOT MADE in the first place.

In summary:

Addition polymers persist for centuries → environmental burden.

Landfill: bad (permanent waste).

Incineration: better with controls; bad without.

Recycling: best but limited and degrading.

Best strategy: REDUCE consumption; reuse where possible; recycle properly; INNOVATE biodegradable / plant-based alternatives; support policy that prices plastic correctly.

The chemistry of polymers — addition vs condensation, the strength of C–C bonds, the lack of biodegradable linkages — explains both their usefulness AND their persistence problem. Engineering better polymers (biodegradable, recyclable) is one of the great chemistry challenges of the 21st century.
Why this scores
Edexcel 6-mark mark scheme: 1 for explaining persistence (C–C bonds, no functional groups for microbes); 1 for landfill problems; 1 for incineration problems (CO₂ + HCl from PVC); 1 for recycling difficulties; 1 for one strategy (reduce/reuse/recycle or biodegradable plastics); 1 for clear discussion of multiple aspects. Mark-scheme keyword: 'non-biodegradable', 'HCl from PVC incineration', 'microplastics'.

Question

4CH1/1C-style — poly(propene)3 marks

Propene has the structural formula CH₂=CHCH₃. (a) Draw the repeat unit of poly(propene). (b) Explain why poly(propene) is described as an addition polymer. (c) State TWO different uses of poly(propene). (3 marks)

Model answer

(a) Repeat unit of poly(propene).

Propene has three carbons: CH₂=CH–CH₃. The C=C double bond is between C1 and C2 (the leftmost two carbons). The –CH₃ group is on C2.

During addition polymerisation, the C=C OPENS up. The two carbons of the former C=C (CH₂ and CH–CH₃) become part of the polymer backbone; the CH₃ group hangs off as a side group.

The repeat unit is:

       ┌──        ──┐
       |   H    H   |
       |   |    |   |
      ─C─ ─ ─C─ ─
       |   |    |   |
       |   H   CH₃  |
       └──        ──┘ ₙ

Or written linearly: ─(CH₂–CH(CH₃))ₙ─ with subscript n outside the brackets.

Key features of the repeat unit:

TWO carbons in the backbone (the former C=C carbons).
One H on the left (–CH₂–).
ONE H + ONE methyl (–CH₃) side group on the right (–CH(CH₃)–).
The C–C between the two main-chain carbons used to be a C=C in propene.
The CH₃ groups on alternate carbons are SIDE CHAINS that hang off the main chain — they don't connect to neighbouring monomers.

(b) Why poly(propene) is an addition polymer.

Poly(propene) is described as an ADDITION polymer because:

The monomer is an ALKENE with a C=C double bond (propene, CH₂=CH–CH₃).
The C=C double bond OPENS UP during polymerisation. The π bond breaks; each carbon of the former double bond now has a free bonding position.
The free positions form bonds to neighbouring monomers. Each propene molecule joins to TWO neighbours, one on each side.
NO ATOMS ARE LOST. Every atom of every propene molecule ends up in the polymer chain. No water, no HCl, nothing eliminated — pure 'addition' of one monomer to the next.

Compare with condensation polymerisation (where a small molecule, usually water, is eliminated at each linkage) — addition polymerisation has 100% atom economy and no byproducts.

The polymerisation equation confirms this:

$n\,\text{CH}_2{=}\text{CHCH}_3 \rightarrow {-}(\text{CH}_2{-}\text{CH(CH}_3))_n{-}$

The same atoms appear on both sides — the only change is the C=C → C–C and the formation of new C–C bonds between former monomers.

(c) TWO uses of poly(propene).

Poly(propene) (also called polypropylene, PP) is one of the world's most-used plastics:

Plastic CONTAINERS — yoghurt pots, takeaway food boxes, microwave-safe containers (poly(propene) has a higher melting point than poly(ethene), so withstands hot food).
Plastic FIBRES — used in carpets, ropes, twine, geotextiles. Strong, durable, water-resistant.
Bottle caps — twist-off caps for plastic and glass bottles (poly(propene) flexes nicely on the threads).
Car parts — bumpers, dashboards, interior trims. Light, tough, mouldable.
Plastic crates and chairs — outdoor furniture, industrial crates.
Living hinges — the flexible plastic hinges on shampoo flip-top caps (poly(propene) can flex thousands of times without breaking — unique among plastics).
Medical supplies — syringes, lab equipment (poly(propene) can be autoclaved/sterilised).

(Pick any TWO for the marks.)

Why these uses match the properties.

Property of poly(propene)	Reason	Use it enables
Tough + flexible	Long polymer chains with side methyls	Containers, fibres
Higher melting point (~ 160 °C) than poly(ethene)	Methyl groups give better packing	Microwave containers, autoclavable equipment
Chemically resistant	Inert C–C/C–H bonds	Food packaging, lab equipment
Cheap	Made in huge volumes from propene (cracking byproduct)	Mass-market consumer goods
Lightweight	Low density (~ 0.90 g/cm³)	Car parts, packaging
Recyclable	Recycling code 5	Sustainable applications

Final summary.

Item	Detail
Monomer	Propene CH₂=CH–CH₃
Repeat unit	─(CH₂–CH(CH₃))ₙ─
Type of polymerisation	Addition (no atoms lost; C=C opens)
Polymer name	Poly(propene), polypropylene, PP
Uses (any 2)	Containers, fibres, bottle caps, car parts, crates

This is the canonical 4CH1 worked example — propene is the second-simplest alkene monomer (after ethene), and poly(propene) is the second-largest-volume plastic in the world. The same logic applies to any other addition polymer (PVC from chloroethene, PTFE from tetrafluoroethene, etc.).

Why this scores

Edexcel 3-mark mark scheme: 1 for correctly drawn repeat unit (with brackets, n, and side methyl group); 1 for explaining 'addition' (C=C opens, no atoms lost); 1 for two valid uses. Common error: drawing the repeat unit with C=C remaining (the polymer has C–C single bond) OR missing the side methyl group on alternating carbons.

Key Definitions and Keywords — Polymers

Definitions to memorise and the exact keywords mark schemes credit for polymers answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE 4CH1 sitting.

Polymer
Examiner keyword
A very LARGE molecule made up of MANY small repeating units (monomers) joined together by chemical bonds. Polymers can have thousands of monomers per chain, giving molecular masses from ~30,000 to several million. Examples: poly(ethene), PVC, nylon, Terylene, proteins, cellulose, DNA.
Monomer
Examiner keyword
A SMALL molecule that can join with OTHER monomers to form a polymer. For ADDITION polymerisation, the monomer is an alkene (has a C=C double bond). For CONDENSATION polymerisation, each monomer has two functional groups (one at each end).
Polymerisation
Examiner keyword
The chemical REACTION by which monomers join together to form a polymer. Two main types: ADDITION (alkenes join via opening of C=C; no atoms lost) and CONDENSATION (two functional groups react with loss of a small molecule like water).
Addition polymerisation
Examiner keyword
A type of polymerisation in which many alkene monomers join together by opening their C=C double bonds. NO ATOMS are lost — every atom of every monomer ends up in the polymer chain. Example: n CH₂=CH₂ → ─(CH₂-CH₂)ₙ─. Products include poly(ethene), poly(propene), PVC, PTFE.
Condensation polymerisation
Examiner keyword
A type of polymerisation in which TWO different monomers (each with TWO functional groups) join together with the loss of a SMALL MOLECULE (usually water) at each linkage. Products: polyesters (from diacid + diol, with ester linkages), polyamides (from diacid + diamine, with amide linkages). Examples: Terylene, nylon, proteins.
Repeat unit
Examiner keyword
The smallest section of a polymer that, when repeated n times, gives the full polymer chain. Drawn in square brackets with subscript n. For poly(ethene): ─(CH₂–CH₂)ₙ─. To identify the monomer from a repeat unit, close the C–C bond between the main-chain carbons back to a C=C.
Polyester (e.g. Terylene / PET)
Examiner keyword
A condensation polymer formed from a dicarboxylic acid + a diol. Each ester linkage (–COO–) forms with loss of water. Example: terephthalic acid + ethylene glycol → Terylene (PET). Used in clothing fibres (mixed with cotton) and PET drinks bottles. Code 1 for recycling.
Polyamide (e.g. Nylon)
Examiner keyword
A condensation polymer formed from a dicarboxylic acid + a diamine. Each amide linkage (–CONH–) forms with loss of water. Example: hexanedioic acid + hexane-1,6-diamine → nylon-6,6. Used in clothing, ropes, parachutes, fishing line, carpets. Similar bond to natural proteins.
Poly(ethene) / polythene
Examiner keyword
An addition polymer from ethene (CH₂=CH₂). Two types: LDPE (low-density, branched, soft, flexible — for bags and films) and HDPE (high-density, linear, harder, stronger — for bottles and pipes). The most-produced plastic in the world. Recycling codes 4 (LDPE) and 2 (HDPE).
PVC = poly(chloroethene)
Examiner keyword
An addition polymer from chloroethene (CH₂=CHCl, also called vinyl chloride). Repeat unit ─(CH₂–CHCl)ₙ─. Uses: rigid pipes, window frames (uPVC), flexible cable insulation, flooring. Concern: releases HCl gas when incinerated → contributes to acid rain.
Non-biodegradable
Examiner keyword
Not broken down by microorganisms or naturally over a reasonable timescale. Addition polymers like poly(ethene), poly(propene), PVC, PTFE are non-biodegradable because they have no functional groups that bacteria can attack — they persist in landfills and oceans for hundreds of years.
Biodegradable plastic
Examiner keyword
A plastic that can be broken down by microorganisms under appropriate conditions (composting). Examples: polylactic acid (PLA) made from corn starch; bioplastics from algae or food waste. Aim: reduce permanent plastic pollution. Many require industrial composting (high T + microbe-rich environment) — won't biodegrade in normal landfill.

Common Mistakes and Misconceptions — Polymers

The traps other students keep falling into on polymers questions — taken from recent Pearson Edexcel IGCSE 4CH1 examiner reports and mark schemes — and how to avoid them.

✕Drawing the repeat unit with the C=C double bond still present
4CH1 Examiner Reports 2022-2024
Why it happens
Copying the monomer too literally.
How to avoid it
Addition polymerisation OPENS the C=C double bond → in the repeat unit, it becomes a C–C SINGLE bond. Always draw the repeat unit with a SINGLE bond between the two main-chain carbons. Example: ethene CH₂=CH₂ → repeat unit ─(CH₂–CH₂)ₙ─ (single bond).
✕Drawing the repeat unit without square brackets and subscript n
4CH1 Examiner Reports 2023-2024
Why it happens
Drawing just the chain.
How to avoid it
ALWAYS include the square brackets [...] and the subscript n (outside the brackets) → tells the marker this is a repeating unit. Without brackets, you've drawn a small molecule, not a polymer's repeat unit.
✕Writing a condensation polymerisation equation without the water byproduct
4CH1 Examiner Reports 2023-2024
Why it happens
Treating it like addition.
How to avoid it
Condensation polymerisation ALWAYS produces a small molecule (usually water) per linkage. For n diacid + n diol → polymer + 2n H₂O. Don't forget the byproduct.
✕Saying condensation polymerisation uses one monomer
4CH1 Examiner Reports 2022-2024
Why it happens
Confusion with addition.
How to avoid it
Addition: ONE monomer (alkene). Condensation: TWO different monomers (each with two functional groups). Some condensation polymers (e.g. silk, polyglycolic acid from one monomer with both –COOH and –OH) seem to use one monomer, but most 4CH1 examples (Terylene from diacid + diol; nylon-6,6 from diacid + diamine) clearly use two different monomers.
✕Confusing 'non-biodegradable' with 'cannot be recycled'
Why it happens
Both relate to disposal.
How to avoid it
Non-biodegradable: microorganisms don't break it down. Persists for centuries. Recyclable: can be melted and re-moulded into new products (some plastics, like PET and HDPE, are widely recycled). A polymer can be both non-biodegradable AND recyclable (most addition polymers fit this — they don't decompose naturally but can be melt-recycled).
✕Saying 'incinerating poly(ethene) releases HCl'
4CH1 Examiner Reports 2023-2024
Why it happens
Confusion with PVC.
How to avoid it
ONLY PVC (poly(chloroethene)) and chlorinated polymers release HCl on incineration — because they CONTAIN chlorine atoms in the repeat unit. Poly(ethene) (just C and H) releases CO₂ + H₂O (clean burn) + soot (incomplete combustion). PTFE releases fluorinated gases. The polymer's incineration products depend on its atoms.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Video lesson

Short walkthrough of the concepts students most often get stuck on.

Polymers — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Polymers

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Define key polymer terms and show with poly(ethene) (4 marks, Paper 1)

2PVC from chloroethene — equation and uses (4 marks, Paper 1)

3Identify the monomer from the repeat unit (3 marks, Paper 1)

4Condensation polymerisation — polyester (5 marks, Paper 2)

5Compare addition vs condensation polymerisation (5 marks, Paper 2)

Polymer

Monomer

Polymerisation

Addition polymerisation

Condensation polymerisation

Repeat unit

Polyester (e.g. Terylene / PET)

Polyamide (e.g. Nylon)

Poly(ethene) / polythene

PVC = poly(chloroethene)

Non-biodegradable

Biodegradable plastic

✕Drawing the repeat unit with the C=C double bond still present

✕Drawing the repeat unit without square brackets and subscript n

✕Writing a condensation polymerisation equation without the water byproduct

✕Saying condensation polymerisation uses one monomer

✕Confusing 'non-biodegradable' with 'cannot be recycled'

✕Saying 'incinerating poly(ethene) releases HCl'

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Polymers — frequently asked questions