What happens when rubber band is heated?

In previous article , we have come to know about thermal expansion. As materials are made of molecules which will be always colliding with each other; heating causes these molecules to collide even harder thus resulting in expansion. When heating stops, materials will contract too . Repetitive expansion and contraction will result in cracks in the material. Rubber bands are different from many other materials as their molecules are very long chains , called polymers. Now because of these unusual structure of polymers , when heating causes the rubber band to get CONTRACT . When these long chains of polymers get hotter and vibrate, they get shorten. This results in contraction of rubber when heated. When the chains cool down , they relax and stretch out resulting in the expansion of rubber band.