Page 33 - Curriculum Visions Dynamic Book

polymer: a compound that is made of long chains by combining molecules (called monomers) as repeating units. (“Poly” means many, “mer” means part).
polymerisation: a chemical reaction in which large number of similar molecules arrange themselves into large molecules, usually long chains. This process usually happens when there is a suitable catalyst present. For example, ethene reacts to form polythene in the presence of certain catalysts.
What makes silicones flexible
Silicon and oxygen together simply make a
material that is hard and brittle, just like quartz.
But by combining the silica with organic materials, the result is a flexible compound that has all the advantages of both silica (it will stand up to high and low temperatures, is not affected by the weather
or ultraviolet light, does not burn) and rubber (it
is flexible, can be moulded, will set into a shape,
is waterproof).
Silicones also have one extra important property: although they repel liquid water, they do allow water vapour to pass through (they are not gastight). This property allows waterproof clothing to “breathe”. People can thus remain comfortable and dry inside waterproof clothing. Similarly, silicones painted on to timber or brick will stay watertight, but they can still breathe.
The only disadvantage of silicones is that they are not quite as flexible or strong as other types of rubber.
Some of the silicone rubbers used in the home
(for example bath and sink sealants) can be squeezed out of tubes. They then set over the next few hours, sticking to the surfaces they have been applied to and curing, which emits a distinctive acrid smell (this is acetic acid gas). Other types of silicone actually cure using moisture from the air.
 Silicone sealant applied to a joint acts both as an adhesive and as water protection.
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