Polymer Formation

Overview

In this lesson (Lesson 15 of 20), students build on earlier ideas about organic chemistry by investigating how addition reactions can form polymers. They focus on how reaction conditions such as heat and pressure help drive polymerisation and shape the properties of the final material.

Learning intentions

• WALT explain addition reactions that form polymers.
• WALT describe the role of heat and pressure during polymerisation.
• WALT use a simple model (monomers → chain growth) to predict products under given conditions.
• WALT record data and justify a conclusion using scientific reasoning.

Success criteria

• I can describe polymerisation as repeating addition of monomer units to form long-chain molecules.
• I can link reaction conditions (heat/pressure) to changes in reaction rate and polymer yield/structure.
• I can interpret model results and write a conclusion that matches the purpose of the investigation.
• I can communicate my method, variables, and reasoning clearly using appropriate scientific language.

Curriculum links

• AS91187 — Carry out a practical Earth and Space Science investigation (used here to match the investigation structure: purpose, method with key variables and ranges, raw data, processed data, conclusion, and reporting).
• NZ Curriculum Science (Level 7/8 intent): students learn to investigate materials and processes using evidence, and communicate science ideas accurately and responsibly.
• Nature of Science: students connect models to real-world chemical processes and evaluate the reliability/limitations of evidence.

Lesson structure (60 minutes)

1. 0–5 min · Starter retrieval. Teacher displays three prompts: “monomer vs polymer”, “addition vs substitution”, “why conditions matter”. Students do a quick write and compare with a partner for corrections.
2. 5–15 min · Direct teaching: addition polymerisation. Teacher models the idea of monomer units joining by addition to form repeating units; emphasise heat/pressure and what they change (rate, collision frequency, reaction completion, and chain growth). Students take guided notes with “claim → evidence → condition”.
3. 15–25 min · Safety + set-up for practical model. Teacher explains today’s practical as a physical/visual model of polymerisation (not a chemical lab), and checks understanding of investigation planning: purpose, key variables, and fair-testing control. Students set up lab sheets and label variables on a diagram.
4. 25–45 min · Practical investigation: “Chain-growth” simulation. Teacher runs a timed station activity where groups use pre-prepared cards/blocks representing monomers and catalyst/condition prompts (e.g., “higher heat”, “higher pressure”, “low heat”, “no pressure/catalyst”). Students record raw counts (e.g., number of successful link-ups or chain length created per round) for each condition, keeping other factors consistent.
5. 45–50 min · Processing data. Teacher shows how to convert raw counts into simple processed data: mean chain length per condition and a basic comparison table/graph. Students calculate summaries and choose the clearest visual representation.
6. 50–57 min · Conclusion and explanation. Teacher prompts students to write a short conclusion linking processed data to the purpose, using scientific vocabulary (addition, repeating units, polymerisation, conditions). Students draft a 1-paragraph conclusion and include “limitations of the model”.
7. 57–60 min · Exit ticket. Teacher gives an exit ticket: “Explain, in 3–5 sentences, how heat and pressure affect polymerisation in an addition reaction.” Students submit before leaving.

Resources

• Polymer model materials (monomer link cards/blocks and chain-length measuring strips)
• Condition prompt cards (e.g., high heat, low heat, high pressure, low pressure, catalyst/no catalyst)
• Group data recording sheets (raw data table for each condition)
• Calculators (or graph paper for manual processing)
• Timer and visual display for rounds
• Student notebooks or printed investigation reporting template
• Safety reminder slides (even though this is a non-chemical model activity)

Assessment

• Formative: teacher circulates during the station activity, checking that students correctly identify key variables and keep them controlled.
• Formative: check processed data accuracy (mean calculations and correctly labelled graph axes).
• Formative: quick review of students’ conclusion paragraph for clear links between evidence, conditions, and polymerisation.
• Summative-in-mini: exit ticket assesses the core understanding of how heat and pressure relate to addition polymerisation and product formation.

Differentiation

• Support: provide sentence starters for WALT/WILF (e.g., “The purpose of this investigation was…”, “The key variable was…”, “When heat increased, we observed…”).
• Support: give a partially completed variables table (independent variable, dependent variable proxy like chain length, controlled variables like round time and mixing rules).
• Extension: ask higher-achieving students to include a “limitations” critique (how the card model differs from real molecular kinetics) and propose one improvement to the method.
• EAL/SEN: allow vocabulary cards (addition reaction, monomer, polymer, repeating unit, polymerisation, heat, pressure, rate) and permit oral reasoning to be written in shorter sentences.