Polymers and sustainable materials

## Big idea: polymers and sustainable materials - **Key concept: Systems.** Polymers consist of long chains built from monomers. Chain structure and interactions affect properties; addition and condensation polymerisation form chains in different ways. - **Related concepts: Models and evidence.** Use a scientific explanation to make predictions, then test it against observations. - **Global context: Scientific and technical innovation.** Polymer selection balances function, durability and end-of-life options. ## Polymers: The Basics - **Polymers** are large molecules made from many smaller **monomers** joined by **covalent bonds**. - Examples: **poly(ethene)**, **PVC**, **nylon**. - Monomers are the repeating units that link to form the polymer chain. ## Addition Polymerisation - **Addition polymerisation** joins monomers containing a **C=C double bond** (alkenes). - The C=C bond breaks, monomers add together, forming a long chain with only **single bonds**. - Only **one product** is formed – the polymer itself. - Example: ethene → poly(ethene). - Polymer name: **poly(monomer name)**, e.g., propene → **poly(propene)**. - To draw a repeat unit: change C=C to C–C, add continuation bonds, and write subscript **n**. ## Deducing Monomer from Polymer (Addition) - Identify the **repeat unit** in the polymer chain. - Change the single bond between repeat units to a **double bond**. - Remove the continuation bonds to reveal the monomer structure. ## Condensation Polymerisation - **Condensation polymerisation** links two different monomers with the removal of a **small molecule** (usually **water**). - Monomers have **two functional groups** (one at each end). - Forms the polymer **plus one water molecule per linkage**. - Examples: **nylon** (polyamide) and **PET** (polyester). ## Nylon – A Polyamide - Nylon is made from a **dicarboxylic acid** (–COOH at both ends) and a **diamine** (–NH₂ at both ends). - Reaction forms an **amide linkage** (–CO–NH–) and releases water. - Represented by boxes for carbon chains with amide links alternating. ## PET – A Polyester - PET (polyethylene terephthalate) is made from a **dicarboxylic acid** and a **diol** (–OH at both ends). - Reaction forms an **ester linkage** (–COO–) and releases water. - Also known as **terylene**; used in plastic bottles and synthetic fibres. - Represented by boxes for carbon chains with ester links alternating. ## Plastics & Their Disposal - Many polymers are **non-biodegradable** – not broken down by microorganisms. - **Incineration**: releases CO₂ (greenhouse gas), may produce toxic fumes (e.g., HCl from PVC) or CO if incomplete. - **Landfills**: take up valuable land; non-biodegradable plastics accumulate. - **Ocean pollution**: plastic waste harms marine life. - **PET recycling**: can be depolymerised by **enzymes** or **chemical catalysts** under mild conditions, then re-polymerised – saves resources and energy. ## Proteins – Natural Polyamides - Proteins are **condensation polymers** of **amino acid** monomers. - Amino acids have both –NH₂ and –COOH groups; the amide link is called a **peptide link**. - Proteins are **natural polyamides**; there are 20 common amino acids with different R groups. - Represented by boxes for carbon chains with peptide links alternating. ## Think like a scientist - A class compares safe polymer packaging strips of equal thickness using a low-force stretching test. - **Comparison:** the polymer material. **Outcome:** extension under a specified force. - **Control:** keep strip length, width and thickness constant. Explain why this makes the comparison fairer. - **Evidence:** Use a consistent method, repeated observations where appropriate and a table with labelled quantities and units. Keep unexpected results and investigate their cause. - **Safety:** Practical activities need teacher supervision and an appropriate risk assessment. Use the provided data or simulation where the investigation specifies it. - **Inquiry task:** State a testable question, predict the outcome using the science, then explain how your observations would support or challenge the prediction. ## Evaluate the science - Polymer selection balances function, durability and end-of-life options. - Biodegradable, recyclable and renewable describe different properties; each claim needs stated conditions and supporting evidence. - **Evaluation task:** Link your conclusion to evidence, identify a limitation and suggest a specific improvement. Distinguish a measured result from an explanation of its cause.