information on rubber

So I have been researching on the materials that balloons are made of. It's actually quite difficult to find information. But this is what I have so far - taken from: http://www.sciencebuddies.org/science-fair-projects/project_ideas/ApMech_p026.shtml

All matter is made up of atoms, like carbon, or hydrogen, or oxygen. Atoms are linked together to form larger compounds called molecules. Some molecules are made by stringing together repeated subunits. Such molecules are called polymers. In some polymers, including many synthetic polymers in textiles and plastics, the subunits are identical. In other polymers, such as proteins manufactured inside cells, the subunits have a common 'backbone' structure, to which different chemical groups are attached.

Rubber is an example of a natural polymer. The chains of molecules in rubber have a natural elasticity: they can stretch when pulled. When the pulling force is removed, the elastic polymers in rubber spring back to their original length. A polymer with elastic properties like this is sometimes called an elastomer. The molecular chains of an elastomer basically act like springs.

Solid materials generally expand when heated and contract when cooled.