Glass Transition Temperature

1. What is glass transition temperature (Tg)?
2. What are the units of glass transition temperature?
3. Which type of polymers undergo glass transition?
4. What are the examples of polymers with high or low Tg?
5. What is the difference between Tg and Tm?
6. Why is it important to identify the Tg of polymers?
7. What are the factors affecting Tg?
8. What are the methods to determine Tg?
9. What are the glass transition values of several plastics?

What is glass transition temperature (Tg)?

The glass transition temperature (Tg) is a phenomenon of amorphous polymers. At this temperature, polymers undergo a transition from glassy to rubbery state. Tg is an important feature of polymer behavior. It marks a region of dramatic changes in the physical and mechanical properties.

• Below Tg: Due to lack of mobility, the polymers are hard and brittle like glass.
• Above Tg: Due to some mobility, the polymers are soft and flexible like rubber.

What are the units of glass transition temperature?

The units of glass transition temperature are:

• Degree Celsius (°C)
• Degree Fahrenheit (°F)
• Kelvin (K)

The value depends on the mobility of the polymer chain. The Tg for most synthetic polymers lies between 170K to 500K.

Which type of polymers undergo glass transition?

Polymers are made up of long chains of molecules. Tg depends on the chemical structure of the polymer defined by its crystallinity. They may be amorphous, crystalline or semi-crystalline.

Amorphous-polymers

Amorphous polymers have a random molecular structure. At Tg, they take the glassy-state properties like brittleness, stiffness, and rigidity (upon cooling). They have a lower Tg than semi-crystalline polymers. This is because their polymeric chains are physically entangled and have spaces between them or at the chain ends. This space is known as free volume which helps polymer chains to move at low temperatures. Higher the free volume lower the glass transition temperature.

They do not have a sharp melting point. As temperature rises the amorphous material softens. These materials are more sensitive to stress failure due to the presence of hydrocarbons. Examples of amorphous polymers are PC, PMMA, PVC, ABS, and GPPS.

Crystalline polymers

Crystalline polymers have a highly ordered molecular structure. They do not soften as the temperature rises, but rather have a defined and narrow melting point (Tm). This melting point is generally above the upper range of amorphous thermoplastics. Examples of crystalline polymers include polyolefins, PEEK, PET, POM, etc.

Semi-crystalline polymers

Semi-crystalline polymers have a combination of random and ordered structures. These ordered structures are crystals that restrict the movement of polymer chains resulting in higher Tg.

Note: Tg is the property of amorphous polymers and the amorphous part of a semi-crystalline solid.

What are the examples of polymers with high or low Tg?

Polymers with high Tg

Some polymers are used below their Tg (in glassy state) like:

• Polystyrene
• Poly(methyl methacrylate)

These polymers are hard and brittle. Their Tg's are higher than room temperature. Learn more about brittle transition temperature »

Polymers with low Tg

Some polymers are used above their Tg (in rubbery state), for example, rubber elastomers like:

• Polyisoprene
• Polyisobutylene

They are soft and flexible in nature. Their Tg's are less than room temperature.

What is the difference between Tg and Tm?

At the molecular level, the chains in amorphous regions of the polymer gain enough thermal energy to begin sliding past one another at a noticeable rate. The temperature where the entire chain movement occurs is called the melting point. It is greater than the Tg.

• Glass Transition is a property of the amorphous region while melting is the property of the crystalline region.
• Below Tg, there exists a 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.

The operating temperature of polymers is defined by transition temperatures.

Why is it important to identify the Tg of polymers?

Glass transition temperature is an important property used to change the physical properties of polymers.

• Increasing Tg improves handling characters, solubility, and reproducibility in the dissolution of solids.
• Changes in physical properties such as hardness and elasticity.
• Changes in volume, percent elongation to break, and Young’s modulus of solids.
• Used for quality control, research, and development.

What are the factors affecting Tg?

Chemical structure

Molecular weight	In straight-chain polymers, increasing molecular weight decreases chain end concentration. This results in the decrease of free volume at the end group region and an increase in Tg.
Molecular structure	Insertion of bulky, inflexible side group increases Tg of material due to a decrease in mobility.
Chemical cross-linking	An increase in cross-linking decreases the mobility of the polymer. This leads to a decrease in free volume and an increase in Tg.
Polar groups	The presence of polar groups increases intermolecular forces, interchain attraction, and cohesion. This leads to a decrease in free volume resulting in an increase in Tg.

Addition of plasticizers

The plasticizers increase the free volume between polymer chains, spacing them apart. The polymer chains slide past each other at lower temperatures resulting in a decrease in Tg.

Water or moisture content

An increase in moisture content forms hydrogen bonds between the polymeric chains. These bonds increase the distance between the chain structures. This results in an increase in free volume and decreases Tg.

Effect of entropy and enthalpy

The value of entropy is high for amorphous material and low for crystalline material. If entropy is high, then Tg is also high.

Pressure and free volume

An increase in pressure of the surrounding leads to a decrease in free volume and ultimately high Tg.

Other factors governing Tg

Other factors have a significant impact on the glass transition temperature of polymers. These include:

• Branching,
• Alkyl chain length,
• Bond interaction,
• Flexibility of polymer chain,
• Film thickness, etc.

What are the methods to determine Tg?

DSC, DTA and DMA are by far the most dominant techniques used for glass transition temperature measurements.

Differential Scanning Calorimetry (DSC)

Differential Scanning Calorimetry (DSC) is a thermo-analytical technique using differential scanning calorimeter. It monitors the difference in heat flow between the sample and reference against time or temperature. It also programs the temperature change of the sample in a specified atmosphere.

DSC determines the thermal properties of the polymer. It applies to amorphous sections of polymers that are stable. These materials do not undergo decomposition or sublimation in the glass transition region.



The test standards used to find Glass Transition Temperature of resins via DSC include:

• ASTM E1356-08(2014) – Standard Test Method for Assignment of the Glass Transition Temperatures by Differential Scanning Calorimetry
• ASTM D3418-15 – Standard Test Method for Transition Temperatures, Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry
• ASTM D6604-00(2017) – Standard Practice for Glass Transition Temperatures of Hydrocarbon Resins by Differential Scanning Calorimetry
• ISO 11357-1:2016 – Plastics — Differential scanning calorimetry (DSC)
• Part 1: General principles
• Part 2: Determination of glass transition temperature and step height

Differential Thermal Analysis (DTA)

Differential Thermal Analysis (DTA) is a popular thermal analysis technique. It is often employed for measuring Tg of the material. This test method is similar to differential scanning calorimetry (DSC). The technique involves an inert reference material.

• The material under analysis in DTA undergoes various heating and cooling (thermal) cycles.
• It determines the temperature difference between the reference and the sample. It maintains the same temperature throughout the heat cycles for reference and sample. This ensures that the testing environment is uniform.

The test standards used to determine Glass Transition Temperature of resins via DTA include:

• ASTM E794-06(2018) – Standard Test Method for Melting and Crystallization Temperatures by Thermal Analysis

Dynamic Mechanical Analysis (DMA)

Dynamic Mechanical Analysis (DMA) uses a dynamic mechanical analyzer to measure the stiffness of materials as a function of temperature, humidity, dissolution media or frequency.



In this technique, a mechanical stress is applied to the sample and the resultant strain is measured by the instrument. These parameters are used to evaluate glass transitions, degree of crystallinity, and stiffness behavior of the sample.

The test standards used to determine Glass Transition Temperature of resins via DMA include:

• ASTM E1640-13 – Standard Test Method for Assignment of the Glass Transition Temperature by Dynamic Mechanical Analysis

Several other methods to determine Tg include:

• Specific heat measurements
• Thermo mechanical analysis
• Thermal expansion measurement
• Micro-heat-transfer measurement
• Isothermal compressibility
• Heat capacity determination

Get Inspired: Learn how to combine data from multiple tools DSC, TGA, DMA, FTIR for Optimal Material Analysis

What are the glass transition temperature values of several plastics?

Click to find polymer you are looking for:
A-C     |      E-M     |      PA-PC     |      PE-PL     |      PM-PP     |      PS-X

Polymer Name	Min Value (°C)	Max Value (°C)
ABS - Acrylonitrile Butadiene Styrene	90.0	102.0
ABS Flame Retardant	105.0	115.0
ABS High Heat	105.0	115.0
ABS High Impact	95.0	110.0
Amorphous TPI, Moderate Heat, Transparent	247.0	247.0
Amorphous TPI, Moderate Heat, Transparent (Food Contact Approved)	247.0	247.0
Amorphous TPI, Moderate Heat, Transparent (Mold Release grade)	247.0	247.0
Amorphous TPI, Moderate Heat, Transparent (Powder form)	247.0	247.0
CA - Cellulose Acetate	100.0	130.0
CAB - Cellulose Acetate Butyrate	80.0	120.0
Cellulose Diacetate-Pearlescent Films	120.0	120.0
Cellulose Diacetate-Gloss Film	120.0	120.0
Cellulose Diacetate-Integuard Films	113.0	113.0
Cellulose Diacetate-Matt Film	120.0	120.0
Cellulose Diacetate-Window Patch Film (Food Grade)	120.0	120.0
Cellulose Diacetate-Clareflect metallized film	120.0	120.0
Cellulose Diacetate-Colored Films	120.0	120.0
Cellulose Diacetate-Flame retardant Film	162.0	162.0
Cellulose Diacetate-High Slip Film	120.0	120.0
Cellulose Diacetate-Semitone Films	120.0	120.0
CP - Cellulose Proprionate	80.0	120.0
COC - Cyclic Olefin Copolymer	136.0	180.0
CPVC - Chlorinated Polyvinyl Chloride	100.0	110.0
EVOH - Ethylene Vinyl Alcohol	15.0	70.0
HDPE - High Density Polyethylene	-110.0	-110.0
HIPS - High Impact Polystyrene	88.0	92.0
HIPS Flame Retardant V0	90.0	90.0
LCP Glass Fiber-reinforced	120.0	120.0
LCP Mineral-filled	120.0	120.0
LDPE - Low Density Polyethylene	-110.0	-110.0
LLDPE - Linear Low Density Polyethylene	-110.0	-110.0
PA 11 - (Polyamide 11) 30% Glass fiber reinforced	35.0	45.0
PA 11, Conductive	35.0	45.0
PA 11, Flexible	35.0	45.0
PA 11, Rigid	35.0	45.0
PA 12 (Polyamide 12), Conductive	35.0	45.0
PA 12, Fiber-reinforced	35.0	45.0
PA 12, Flexible	35.0	45.0
PA 12, Glass Filled	35.0	45.0
PA 12, Rigid	35.0	45.0
PA 46, 30% Glass Fiber	75.0	77.0
PA 6 - Polyamide 6	60.0	60.0
PA 66 - Polyamide 6-6	55.0	58.0
PA 66, 30% Glass Fiber	50.0	60.0
PA 66, 30% Mineral filled	50.0	60.0
PA 66, Impact Modified, 15-30% Glass Fiber	50.0	60.0
Polyamide semi-aromatic	115.0	170.0
PAI - Polyamide-Imide	275.0	275.0
PAI, 30% Glass Fiber	275.0	275.0
PAI, Low Friction	275.0	275.0
PAR - Polyarylate	190.0	190.0
PBT - Polybutylene Terephthalate	55.0	65.0
PC (Polycarbonate) 20-40% Glass Fiber	150.0	150.0
PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant	150.0	150.0
PC - Polycarbonate, high heat	160.0	200.0
PCL - Polycaprolactone	-60.0	-60.0
PE - Polyethylene 30% Glass Fiber	-110.0	-110.0
PEEK - Polyetheretherketone	140.0	145.0
PEEK 30% Carbon Fiber-reinforced	140.0	143.0
PEEK 30% Glass Fiber-reinforced	143.0	143.0
PEI, Mineral Filled	215.0	215.0
PEI, 30% Glass Fiber-reinforced	215.0	215.0
PEI, Mineral Filled	215.0	215.0
PESU - Polyethersulfone	210.0	230.0
PESU 10-30% glass fiber	210.0	230.0
PET - Polyethylene Terephthalate	73.0	78.0
PET, 30% Glass Fiber-reinforced	56.0	56.0
PETG - Polyethylene Terephthalate Glycol	79.0	80.0
PFA - Perfluoroalkoxy	90.0	90.0
PGA - Polyglycolides	35.0	40.0
PHB-V (5% valerate) - Poly(hydroxybutyrate - co- valerate)	3.0	5.0
PI - Polyimide	250.0	340.0
PLA, Fiber Melt Spinning	55.0	65.0
PLA, Heat Seal Layer	52.0	58.0
PLA, Injection molding	55.0	60.0
PLA, Spunbond	55.0	60.0
PLA, Stretch blow molded bottles	50.0	60.0
PMMA - Polymethylmethacrylate/Acrylic	90.0	110.0
PMMA (Acrylic) High Heat	100.0	168.0
PMMA (Acrylic) Impact Modified	90.0	110.0
PMP - Polymethylpentene	20.0	30.0
PMP 30% Glass Fiber-reinforced	20.0	30.0
PMP Mineral Filled	20.0	30.0
POM - Polyoxymethylene (Acetal)	-60.0	-50.0
PP - Polypropylene 10-20% Glass Fiber	-20.0	-10.0
PP, 10-40% Mineral Filled	-20.0	-10.0
PP, 10-40% Talc Filled	-20.0	-10.0
PP, 30-40% Glass Fiber-reinforced	-20.0	-10.0
PP (Polypropylene) Copolymer	-20.0	-20.0
PP (Polypropylene) Homopolymer	-10.0	-10.0
PP, Impact Modified	-20.0	-20.0
PPE - Polyphenylene Ether	100.0	210.0
PPE, 30% Glass Fiber-reinforced	100.0	150.0
PPE, Impact Modified	130.0	150.0
PPE, Mineral Filled	100.0	150.0
PPS - Polyphenylene Sulfide	88.0	93.0
PPS, 20-30% Glass Fiber-reinforced	88.0	93.0
PPS, 40% Glass Fiber-reinforced	88.0	93.0
PPS, Conductive	88.0	93.0
PPS, Glass fiber & Mineral-filled	88.0	93.0
PPSU - Polyphenylene Sulfone	220.0	220.0
PS (Polystyrene) 30% glass fiber	90.0	120.0
PS (Polystyrene) Crystal	90.0	90.0
PS, High Heat	90.0	90.0
PSU - Polysulfone	187.0	190.0
PSU, 30% Glass fiber-reinforced	187.0	190.0
PSU Mineral Filled	187.0	190.0
PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced	60.0	100.0
PVC, Plasticized	-50.0	-5.0
PVC, Plasticized Filled	-50.0	-5.0
PVC Rigid	60.0	100.0
PVDC - Polyvinylidene Chloride	-15.0	-15.0
PVDF - Polyvinylidene Fluoride	-42.0	-25.0
SAN - Styrene Acrylonitrile	100.0	115.0
SAN, 20% Glass Fiber-reinforced	100.0	115.0
SMA - Styrene Maleic Anhydride	110.0	115.0
SMA, 20% Glass Fiber-reinforced	110.0	115.0
SMA, Flame Retardant V0	110.0	115.0
SRP - Self-reinforced Polyphenylene	150.0	168.0