 Polymers Noadswood Science, 2011

Polymers  To be able to describe how plastics and other polymers are made from alkenes Tuesday, April 21,

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 +

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 together Polymer 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 PolymerUse PolyethenePlastic bags and bottles PolypropeneCrates and ropes Polychloroethene Water 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