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We know that water has the three physical states of solid, liquid, and gas. And we are likely familiar with the state changes such as melting, freezing, boiling (vaporization), and condensation. The large molecules of polymers do not follow the classical physical states and phase transitions observed by small molecules.
Below is an overview of how polymers change as heat is applied.
Soften: as heat is added, polymers change from a stiff solid at low temperatures to a soft pliable material at the glass transition temperature, Tg.
Melt: similar to the wax of a candle, crystalline polymers can melt when heated but usually at relatively high temperatures. Some polymers are amorphous and do not show a clear melt transition, Tm.
Decompose: polymers do not vaporize (become a gas) after melting, they breakdown or depolymerize into smaller molecules (fragments) at high temperatures.
Burn: for many commodity polymers the fragment vapors will burn in the presence of oxygen and heat (ignition source)
Soot: some polymers produce large amounts of soot when they burn
Here is the study material about glass transition temperature Download
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