Plastics: chains and cross-linking
About this app
Three samples of the same chains on a hot plate: the thermoplastic flows, the elastomer springs back, the thermoset breaks and decomposes. Set the degree of cross-linking, build chains by radical polymerisation and polycondensation, match properties and reason from properties to structure.
With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.
What it is about
Plastics consist of long chains, and their behaviour depends above all on cross-linking. Thermoplastics have no cross-links, and only intermolecular forces hold the chains together. When heated they slide past each other, so the material can be melted and reshaped. Elastomers are loosely cross-linked and spring back after stretching. Thermosets are densely cross-linked, do not melt and decompose under strong heat.
What the app shows
Three samples of the same ball-and-spring chains stand on a hot plate, on the left without cross-links, in the middle with a few, on the right with many. The chains stretch when pulled and slide only where nothing holds them. In the build scene chains grow step by step: radical polymerisation of ethene, polycondensation to polyester and polyamide with water split off. The model is simplified: melting at 110 °C follows PE-LD, further limits are assumptions, and the app does not show the glass transition.
What you try out
You move the slider on the hot plate and pull the handles. For a single sample you set the degree of cross-linking and see a thermoplastic become an elastomer and a thermoset. You reshape solidified melt. You drag monomers to the chain end, match properties to the three classes and answer nine questions that reason from properties to structure.
Frequently asked questions
- What is the difference between thermoplastics, elastomers and thermosets?
- Thermoplastics consist of linear or slightly branched chains without cross-links and can be melted. Elastomers are loosely cross-linked and rubber-elastic. Thermosets are densely cross-linked, hard and do not melt. All three can be built from similar chains, and the difference lies in the cross-links.
- Why does a thermoset not melt?
- Its chains are joined by covalent bonds into a tight network. They cannot slide past each other. Under strong heating bonds break before the material could flow, so it decomposes.
- How do you recognise a polycondensation?
- Monomers with two functional groups each join up, and for every new ester or amide group a small molecule such as water is split off. In radical polymerisation, by contrast, C=C double bonds open and there is no by-product.
- What can I do in the app myself?
- You heat and stretch samples, change the degree of cross-linking, build chains from monomers and match properties. An explain mode guides you through the three classes.
Subject: Chemistry
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