MYP Chemistry: Polymers & Plastics — FAQs

A polymer is a large molecule built from many repeating smaller units called monomers, joined by covalent bonds into long chains. In MYP Chemistry you meet natural polymers, like starch and proteins, alongside synthetic ones, like polyethene and PET — the same repeating-unit logic drives all of them.

Addition polymerisation joins monomers containing a C=C double bond, with no by-product — polyethene from ethene is the classic MYP example. Condensation polymerisation joins monomers carrying two reactive functional groups, releasing a small molecule (usually water) each time a new bond forms — nylon is the standard case.

Chain length, branching, and how tightly chains pack together decide a plastic's properties. HDPE has straight, closely-packed chains that give it rigidity and a higher melting point; LDPE has branched chains that pack loosely, making it softer and more flexible. Same monomer, ethene — different chain arrangement, different plastic entirely.

Thermoplastics soften when heated and can be remoulded repeatedly because their chains aren't chemically cross-linked — polyethene and PVC are typical examples. Thermosets form permanent cross-links during curing, so they char rather than melt once set — an electrical socket casing made from Bakelite is the go-to example.

It's assessed against the same four MYP Sciences criteria as any unit: Criterion A tests your understanding of monomer/polymer structure and reactions, Criterion B assesses inquiry skills through investigation design, Criterion C evaluates your data handling, and Criterion D asks you to weigh the environmental impact of plastic use.

Expect 'describe', 'explain', 'compare and contrast', and 'discuss' most often on polymer tasks. 'Describe' wants a factual account of structure or process; 'explain' wants the reasoning behind it, why LDPE is flexible, say; 'discuss', usually Criterion D, wants you to weigh evidence for and against, not just state an opinion.

A strong Criterion D task asks you to evaluate a real issue — whether banning single-use plastic bags actually reduces environmental harm, for instance — using scientific reasoning plus a named global context, usually Globalisation and Sustainability. You need balanced evidence, not just an opinion, to reach the top achievement band.

Start by being able to draw a repeat unit from a given monomer and vice versa — that single skill underpins most exam questions. Then work through past criterion-style tasks rather than re-reading notes; this topic rewards practising the reasoning behind an answer far more than memorising isolated facts.

The biggest one I see marking these: students forget to open the double bond correctly when drawing an addition polymer's repeat unit, leaving a dangling bond. The second: confusing monomer with repeat unit — the repeat unit is what's left after the bond forms, not the original monomer structure itself.

No — you need to be able to derive them. Give me any monomer with a C=C bond and you should be able to open that double bond, add a bond either side, and bracket the repeat unit with 'n' outside. Mastering that one process beats memorising half a dozen separate structures.

It depends what you mean by 'better' — biodegradable doesn't automatically mean low-impact. Some bioplastics need industrial composting conditions most households can't provide, and the land used to grow plant-based feedstock has its own environmental cost. Criterion D tasks expect you to weigh these trade-offs, not just repeat 'bioplastics are green'.

The monomer-to-polymer reasoning built in MYP 4-5 carries straight into DP Chemistry, where polymers sit under Structure 2.4, From Models to Materials, in the current syllabus first examined in 2025. DP pushes further into naming conventions and mechanism detail, but the addition/condensation distinction learned now doesn't change at all.

You don't need a chemistry background — ask your child to explain a plastic they use every day, a water bottle, a shopping bag, in terms of monomer, polymer and properties. If they can't do it in plain language, that's the actual gap to target with practice questions, not more re-reading.

Past criterion-style tasks matter more than generic notes at MYP 4-5, since marks depend on applying knowledge to a criterion descriptor, not just recalling facts. Look for Revision Notes and Topical Worksheets organised around Criteria A-D specifically for this topic, so practice mirrors exactly how polymers & plastics gets marked.