Question

Glass Transition Temperature and Molecular Motion

List the order of the glass transition temperatures for polyethylene, polypropylene, polyvinyl chloride, and polystyrene.   PE (-80), PP (-20), PVC (85), PS (100).

Define the glass transition temperature in polymer materials. –

Describe the reason for this vast range of glass temperatures among these 4 materials.

Answer 1

Order of glass transition temperatures:

Polyethylene: -130 to 80C

Polypropylene: -20 to -10C

Poyvinyl chloride:100 to 110 C

Polystyrene: 88 to 92C

Glass transitition temperature:

It is the temperature at which the polymers change from a glassy state to rubbery state. It is analogous to melting point for pure substances. But at melting point complete phase change has occured while at glass transition temperature phase change only begins

The reason for the vast range of glass temperature values is that unline melting which is phase change at a single temperature, glass transition from liquid to solid does not occur at a single temperature. These glassy materials slowly change from liquid to solid having a rubbery state inbetween. This is because of the molecular weight of materials which exists in wide range unlike a pure substance which exhibits single molecular weight. Since there is materials with a range of molecular weight, these glassy polymers cannot undergo phase transition at a single temperature like the pure substances.