Polymers

Noadswood Science, 2011

Polymers

To be able to describe how plastics and other polymers are made from alkenes

Tuesday, April 18, 2023

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Plastics

What are plastics – how are these made, and why are they so useful?

Plastics are polymers (huge molecules which are made up of lots of smaller molecules (monomers) which have been joined together)

Different types of plastics can be made by using different monomers – these plastics can have very different properties…

*Plastic surgery is not connected with polymers: the name derives from the Greek plastikos meaning to mold /shape

Nylon

Nylon was the first commercially successful synthetic polymer – a thermoplastic (softens when heated) silky material originally used in toothbrushes and later as tights…

It is formed when a combination of smaller molecules join together: two solutions with different densities are layered

A film of nylon appears instantly where the two layers meet

Monomer Polymer

Alkenes can be used to make polymers

Polymers are very large molecules made when many smaller molecules join together, end-to-end

The smaller molecules are called monomers

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Monomer Polymer

Polymer: Poly(ethene) - polythene

Many ethene monomers can join end-to-end to make poly(ethene) or polythene

Initially the C=C double bond of the ethene must be broken, and then the molecules can be added together…

Monomer Polymer

Initially the alkene double bond (C=C) is

broken

Monomers are joined togetherPolymer formed

Monomer Polymer

Polymer: Poly(chloroethene) – PVC

Many chloroethene monomers can join end-to-end to make poly(chloroethene) or PVC…

Alkenes

Alkenes can act as monomers because they have a double bond: - Ethene can polymerise to form poly(ethene) (polythene) Propene can polymerise to form poly(propene) (polypropylene)

Different polymers have different properties, so they have different uses…

Polymer Uses

Polymer Use

Polyethene Plastic bags and bottles

Polypropene Crates and ropes

PolychloroetheneWater pipes and insulation on

electricity cables

Slime

Complete the slime experiment: -

Add a few drops of the borax solution to a warm solution of PVA glue (you can add some food colouring if you wish to enhance the appearance)

Stir well for at least 2 minutes…

*The glue becomes slimy because the borax makes the long polymer chains in the glue link together, forming a jelly-like substance

Properties

Different polymers can be made by using different monomers – these polymers can have very different properties…

Polymers have properties that depend on the chemicals they are made from, and the conditions in which they are made – modern polymers have many uses, including: - Waterproof coatings Fillings for teeth Dressings for cuts Hydrogels for making soft contact lenses and disposable

nappy liners Shape memory polymers for shrink-wrap packaging

Plasticisers & Slime

Plasticisers are substances that let the polymer molecules slide over each other more easily making the polymer softer and more flexible

Poly(chloroethene) or PVC is a hard polymer: - Unplasticised PVC (uPVC) is used to make pipes and

window frames PVC with plasticisers is soft and flexible and is used

for floor coverings, raincoats and car dashboards

Plasticisers & Slime

Poly(ethenol) is a polymer that dissolves in water to make slime: the viscosity of the slime can be changed to make it thick or runny by varying the amount of water

Thermosoftening & Thermosetting

Polymers can fall into two categories: - Thermosoftening – can be heated and shaped many times Thermosetting – can only be heated and shaped once

Thermosetting polymers have their chains cross linked by covalent bonds – the polymer is originally placed into a mould and heated causing cross links to form (further heat will not cause the polymer to soften or change shape)

Thermosoftening & Thermosetting

• Thermosoftening (top) and thermosetting (bottom) showing the cross link bonds which causes it to hold it’s shape