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Use of Alkenes

  • Date Submitted: 10/02/2011 10:33 AM
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Use of Alkenes
Alkenes can polymerise, they do this by joining together to form long chains with very high relative molecular masses which can reach up to 1,000,000.

C2H4 which is ethane, will be polymerised into poly(ethene), this reaction is shown in the diagram below.
Repeating Units of the reaction below (C2H4 C2H4) would be shown in a diagram as shown.

Polymerisation of ethene into poly(ethene)

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Properties of Addition Polymers
Low Density Additional Polythene – is made by polymerising ethene (C2H4), and a high temperature and pressure by a free-radical mechanism. The polymer   that is made will have a certain chain length that is unknown. This is a result of the way free radical reactions work. The Hydrocarbon chain has fairly many branched chains, and because they do not pack together well, it gives it a low density and so therefore a product which is flexible and is able to stretch. This gives it the properties for items like plastic bags, sheeting and insulation for electrical cables.

High density Additional Polythene – This is made in completely different conditions to the Low Density Additional Polymers, the temperature and pressure during this reaction is only slightly higher than room conditions, and Ziegler-Natta catalysts (or other metal compounds) are used. These catalysts help control the chain length and therefore less random and more controlled. This also causes less chain branching. These branches are able to pack together, and so it makes the density of the plastic and the melting point much higher. This plastic can be used for plastic crates, milk bottles and similar containers, washing up bowls, plastic pipes and buckets, this plastic is used on these materials as Low Density Additional Polymers, would be to rigid.
Recycling of Polymers
The problem with plastics is the fact they aren’t biodegradable, most plastics cannot even be broken down by microbes, unlike some which very slowly can be, and so now...


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