What does Tg stand for?

Amorphous polymers only exhibit a Tg.

Crystalline polymers exhibit a Tm (melt temperature) and typically a Tg since there is usually an amorphous portion as well (“semi”-crystalline).

Check out more on Glass Transition Temperature:

» Glass Transition Temperature Values Table of Several Plastics

» How to Determine Glass Transition Temperature

» Key difference Between Tg and Melting Temperature

» Factors Affecting Tg of any plastic

Amorphous Polymers and Crystalline Polymers

Semi-crystalline polymers

How to Measure Glass Transition Temperature

In DTA, the difference in temperature between the sample and a reference material is monitored against time or temperature while the temperature rise/fall of the sample, in a specified atmosphere, is programmed.



In DSC, the difference in heat flow to a sample and to a reference is monitored against time or temperature while the temperature rise/fall of the sample, in a specified atmosphere, is programmed.

Glass Transition Temp. Measurements of Different Polymers Using DSC

(Source: Mettler-Toledo Analytical)

Specific heat measurements



Thermo mechanical analysis



Thermal expansion measurement



Micro-heat-transfer measurement



Isothermal compressibility



Heat capacity



Glass Transition Temperature Vs Melting Temperature

Glass Transition is a property of the amorphous region while melting is the property of crystalline region Below Tg, there exists disordered amorphous solid where chain motion is frozen and molecules start wiggling around above Tg. The more immobile the chain, the higher the value of Tg. While, below Tm it is an ordered crystalline solid which becomes disordered melt above Tm

Factors Affecting Tg

Chemical Structure

Molecular Weight – In straight chain polymers, increase in MW leads to decrease in chain end concentration resulting in decreases free volume at end group region – and increase in Tg

– In straight chain polymers, increase in MW leads to decrease in chain end concentration resulting in decreases free volume at end group region – and increase in Tg Molecular Structure - Insertion of bulky, inflexible side group increases Tg of material due to decrease in mobility,

- Insertion of bulky, inflexible side group increases Tg of material due to decrease in mobility, Chemical cross-linking - Increase in cross-linking decreases mobility leads to decrease in free volume and increase in Tg

- Increase in cross-linking decreases mobility leads to decrease in free volume and increase in Tg Polar groups - Presence of polar groups increases intermolecular forces; inter chain attraction and cohesion leading to decrease in free volume resulting in increase in Tg.

Addition of Plasticizers

Water or moisture content

Effect of entropy and enthalpy

Pressure and free volume

Glass Transition Temperature Values of Several Plastics