Explain why the properties of a polymer below the glass transition temperature are different from the same properties in the same polymer above the glass transition temperature.

At low temperatures (below the glass transition temperature) crystalline polymers are rigid like glass. This happens because all the polymer chains are perfectly arranged, all the polymer is in the crystalline form. On the other hand, when the temperature raises, upper the glass transition temperature, some polymer chains start to get loose and form some amorphous regions in between the crystalline regions of the polymer. This condition makes the polymer more flexible.