L5 - Addition Polymerisation

objectives

1. understand how polymers are formed from alkenes
2. recognise monomers from the polymer structure

Polymers

Polymers are very large molecules built up from small molecules called monomers.

Natural polymers

e.g. proteins, starch, DNA, cellulose

Synthetic polymers

e.g. Polythene, PVC, polyester etc.

POLYMERS can also be made from only one type of MONOMER

Addition Polymerisation

Alkenes can polymerise by a process called addition polymerisation

e.g. Ethene polymerises to form poly(ethene)

The polymer is named from the monomer unit

The repeating unit is shown in brackets (the smallest group of atoms that produce the polymer when repeated over and over)

You can see from the above diagram that the Double Bond essentially opens up - giving the monomers the ability to repeatedly bond with each other - for all intensive purposes - in a straight line that can go on for many thousands of monomers.

The n in the above diagram represents any large number.

The brackets on the repeating unit above represent that monomers are joined via those bonds - these are ALWAYS either side of a double bond.

Polymers and Monomers

Addition polymers are made from monomers with a carbon-carbon double bond i.e. Molecules based on ethene

Spotting Alkene Monomers

Spotting monomers from an extended polymer chain is actually quite simple:

• Look for the Repeating Pattern
• Draw a Double bond inside the repeating pattern
• Break the ends by removing the joining bonds to the next monomer

Problems with Polymers

Although polymers derived from alkenes are invaluable to modern society, their disposal creates widespread problems.

• they are unreactive to most chemicals and bacteria (non-biodegradable)

• if they are just discarded they add to the landfill problem