# Polymers

> Addition polymers (polyethylene, PVC, polystyrene, PTFE) and condensation polymers (polyesters, polyamides such as nylon and Kevlar), how structure decides properties, and the problems and benefits of plastics.

From HSC Chemistry on WhizzNotes, free study notes for NSW students: https://whizznotes.com/chemistry/polymers/. Updated 3 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: The accident that made Teflon
In 1938, Roy Plunkett, a young chemist in the USA, opened the valve on a cylinder of a gas he was storing. Nothing came out, yet the cylinder was still heavy. He sawed it open and found a slippery white powder inside.

The gas molecules had joined together into enormously long chains. The powder was **PTFE**, later sold as Teflon, the non-stick coating on frying pans. It is a **polymer**: a giant molecule built from thousands of small repeating units called **monomers**, like a long train made of identical carriages.

**In short:** A polymer is a long chain made of many small repeating molecules called monomers. Addition polymers like polyethene form from alkenes with nothing else made, while condensation polymers like nylon and polyesters give off water as each link forms.

## Monomers and polymers

- A **monomer** is a small molecule that can join to others.
- A **polymer** is a very long molecule made of many monomers joined by covalent bonds.
- **Polymerisation** is the reaction that joins them.

There are two kinds: **addition** and **condensation**.

## Addition polymers

Monomers with a **C=C double bond** open the double bond and join end to end. **Nothing else is produced**.

$$n\,\mathrm{CH_2{=}CH_2} \rightarrow \mathrm{{-}(CH_2{-}CH_2)_{n}{-}}$$

ethene → polyethylene

| Polymer | Monomer | Properties | Uses |
|---|---|---|---|
| **Polyethylene** (PE) | ethene $\mathrm{CH_2{=}CH_2}$ | Flexible, cheap, waterproof | Bags, bottles, cling wrap |
| **Polyvinyl chloride** (PVC) | chloroethene $\mathrm{CH_2{=}CHCl}$ | Strong, rigid, waterproof, electrical insulator | Pipes, window frames, cable coating |
| **Polystyrene** (PS) | phenylethene (styrene) | Rigid; can be expanded into a light foam | Foam cups, packaging, insulation |
| **PTFE** (Teflon) | tetrafluoroethene $\mathrm{CF_2{=}CF_2}$ | Non-stick, very unreactive, high melting point | Non-stick pans, plumbing tape |

**Drawing the polymer**: draw the monomer's carbon chain with the C=C as a single bond, put brackets around one repeat unit, and add "n". For three repeat units of PVC, draw six carbons in a row with a Cl on every second carbon.

## LDPE and HDPE

Polyethylene comes in two forms, depending on how it is made:

| | LDPE (low density) | HDPE (high density) |
|---|---|---|
| Chains | Lots of **branches** | Few branches, **straight** chains |
| Packing | Chains cannot pack closely | Chains pack tightly, in neat crystalline regions |
| Dispersion forces | Weaker | Stronger |
| Properties | Soft, flexible, lower melting point | Harder, stronger, more rigid, higher melting point |
| Uses | Plastic bags, cling wrap | Milk bottles, buckets, pipes |

## Condensation polymers

Monomers with **two functional groups** (one at each end) join, and a **small molecule** (usually **water**) is released at every link.

**Polyesters** form from a **diol** (two −OH groups) and a **dicarboxylic acid** (two −COOH groups). Each link is an **ester** group. Example: **PET**, used in drink bottles and polyester clothing.

**Polyamides** form from a **diamine** (two −NH₂ groups) and a **dicarboxylic acid**. Each link is an **amide** group, −CONH−. Examples:

- **Nylon 6,6**: strong, elastic fibres for clothing, ropes and carpets.
- **Kevlar**: ring-shaped monomers make rigid, flat chains that line up and hydrogen bond strongly to each other. It is five times stronger than steel by weight and is used in bulletproof vests.

Natural condensation polymers include **proteins** (polyamides of amino acids), **cellulose** and **starch** (from glucose).

A single monomer with both groups can also polymerise by itself. For example, lactic acid (with −OH and −COOH) forms **PLA**, a biodegradable polyester.

## Structure and properties

| Feature | Effect |
|---|---|
| Longer chains | More dispersion forces, so stronger and higher melting point |
| Branching | Looser packing, so softer and lower melting point |
| Polar groups (like C−Cl in PVC) | Dipole-dipole forces, so more rigid |
| Hydrogen bonding between chains (nylon, Kevlar) | Very strong fibres |
| Bulky side groups (polystyrene) | Stiff chains |

## Plastics and the environment

- Most synthetic polymers are made from **crude oil** (non-renewable).
- They are **not biodegradable**, so they last for hundreds of years in landfill and oceans, and break into microplastics.
- Burning PVC releases toxic HCl gas.
- **Recycling** and **biopolymers** (such as PLA, or PHB made by bacteria from sugar) help. Biopolymers come from renewable sources and break down.

**Mind map**

```text
Polymers
  Basics
    Monomer, polymer
    Repeat unit, n
  Addition
    C=C monomers
    No by-product
    PE, PVC, PS, PTFE
  LDPE vs HDPE
    Branched, soft
    Straight, strong
  Condensation
    Two functional groups
    Water released
    Polyester: diol + diacid
    Polyamide: diamine + diacid
    Nylon, Kevlar, PET
  Properties
    Chain length
    Branching
    Hydrogen bonds
  Environment
    From oil
    Not biodegradable
    Biopolymers
```

### Year 11: Molar mass of a polymer
The molar mass of an addition polymer is the monomer's molar mass times the number of units:

$$MM(\text{polymer}) = n \times MM(\text{monomer})$$

**Example.** A sample of PVC has a molar mass of 125 000 g/mol. Chloroethene, $\mathrm{C_2H_3Cl}$, has a molar mass of 62.49 g/mol. So $n = 125\,000 \div 62.49 = 2000$ monomer units.

**From polymer back to monomer.** Find the repeating two-carbon unit and put the double bond back. $\mathrm{-CH_2{-}CH(CH_3){-}CH_2{-}CH(CH_3){-}}$ repeats $\mathrm{CH_2CH(CH_3)}$, so the monomer is propene, $\mathrm{CH_2{=}CHCH_3}$.

**No double bond left.** Polyethylene has only single bonds, so it does **not** decolourise bromine water, while ethene does.

**Same percentage of carbon.** An addition polymer is just its monomer units joined, with no atoms lost, so it has exactly the same percentage of carbon by mass as the monomer.

### Year 12: Condensation calculations and Kevlar
In a condensation polymer, each new link loses a water molecule, so the **repeat unit is lighter** than the monomers that made it.

**Example.** 4-aminobutanoic acid, $\mathrm{H_2N(CH_2)_3COOH}$ (103.12 g/mol), polymerises. Each repeat unit is the monomer minus $\mathrm{H_2O}$: $103.12 - 18.02 = 85.10$ g/mol. A chain of 100 units has a molar mass of about $100 \times 85.10 = 8.5 \times 10^3$ g/mol.

**Why Kevlar is so strong.** Its benzene rings keep each chain straight and rigid. The chains line up side by side, and the N−H of one chain hydrogen bonds to the C=O of the next. Millions of these hydrogen bonds make a sheet-like structure that resists stretching. Nylon has flexible $\mathrm{CH_2}$ sections, so it stretches more.

**Two monomers.** For nylon 6,6, one repeat unit comes from one diamine and one diacid, losing **two** waters: $116.20 + 146.14 - 2 \times 18.02 = 226.30$ g/mol.

**Counting units.** Divide by the repeat unit mass, not the monomer mass. PHB's monomer is 104.10 g/mol, so its repeat unit is $104.10 - 18.02 = 86.08$ g/mol, and a chain of $8.6 \times 10^4$ g/mol has about 1000 units.

## Quick summary

- Polymers are long chains of repeating monomers.
- Addition polymers form from alkenes; nothing else forms. Examples: PE, PVC, PS, PTFE.
- LDPE is branched and soft; HDPE has straight chains and is stronger.
- Condensation polymers release water: polyesters (diol + diacid) and polyamides (diamine + diacid).
- Hydrogen bonds between chains make nylon and Kevlar strong.
- Most plastics come from oil and do not biodegrade; biopolymers are an alternative.

## Quiz

Try these questions from the chapter quiz.

1. A polymer is:
   - A. A long chain made of many repeating units
   - B. A small molecule with a double bond
   - C. An ionic compound
   - D. A mixture of metals
   - Answer: A. A long chain made of many repeating units. Poly means many.

2. Addition polymers form from monomers that contain:
   - A. An −OH group
   - B. A C=C double bond
   - C. Two −COOH groups
   - D. An amide group
   - Answer: B. A C=C double bond. The double bond opens to link the monomers.

3. The monomer of polyethylene is:
   - A. Ethane
   - B. Ethene
   - C. Ethanol
   - D. Ethyne
   - Answer: B. Ethene. $\mathrm{CH_2{=}CH_2}$.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/chemistry/polymers/#quiz