TGA (ThermoGravimetric Analysis) only gives, as you say, changes in sample mass as temperature is increased as result of thermal decomposition or the loss of volatiles etc. from the sample. In a pure polymer there is no mass change as a result of crossing the glass transition temperature (T_g), so TGA will not be much use to you for the purpose of T_g determination.

The most commonly utilised method for the determination of T_g is differential scanning calorimetry (DSC), from which the change in specific heat capacity of the polymer across T_g can be determined, the temperature at which this occurs (commonly the onset or midpoint of the change upon second heating of the sample is used) is denoted as T_g. Dynamic Mechanical Analysis (DMA) is also commonly utilised but DSC is more "straightforward".  

Any experimental method used to ascertain a value of T_g certainly requires an appreciation and "basic understanding" of the physics of the glass transition as well as considerations to how experimental parameters and other sample properties influence the measurement.

Quite a general response but I hope it helps!

Dave

In principle, there is no mass change directly associated to Tg, so that Thermogravimetric analysis (TGA) can not be expected to detect Tg, in general.

Note, however, that specific circumstances may possibly occur, that may allow for some degree of Tg sensitivity, such as when the sample is previously swelled by moisture or by some organic solvent, which drying rate may then be somehow affected while crossing the glass transition region. Such effect may be better detected at the dTG/dt plot, although such detection may be only approximate.

It may be found worthy to check also the following discussion, also for a dTG/dt detected effect, yet (seemingly) experimental artifact related: https://www.researchgate.net/post/How_can_I_interpret_many_oxidation_waves_on_amorphous_silicon_TGA

The following paper discusses the glass transition:

Article Aspects of the non-crystalline state

Thermogravimetric Analysis(TGA) measures the amount of weight change of a material, either as a function of increasing temperature, or isothermally as a function of time, in an atmosphere of nitrogen, helium, air, other gas, or in vacuum.TGA can not  measure  detect Tg. Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) may detect Tg.DSC and DTA are thermoanalytical techniques. Both have almost the same applications and usages in analysis, but the techniques involved in the analysis are different. One is based on the temperature difference while the other is based on the heat flow difference.

DTA  quantitatively analyze the chemical composition of substances by observing the thermal behavior of a sample which  undergoes reactions and phase changes that involve absorption or emission of heat. DTA is suited for the determination of characteristic temperatures. In  DSC  technique, the difference is calculated between the amount of  heat needed to increase the temperature of the sample and the heat required to increase the temperature of the reference. DSC allows for the determination of caloric values such as the heat of fusion or heat of crystallizationDSC and DTA  are both  used in measuring a glass transition, phase changes, purity evaporation, melting, purity crystallization, sublimation, pyrolysis .You can get Tg  using DTA or DSC as  doc below show

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I agree with above comments, with only TGA we get complete weight changes (weight%) by heating the sample in the form of dehydration, decomposition. Rate of weight change with respect to temperature (dW/dT) or with respect to time (dW/dt) if isothermal balancing is used. Whereas in DSC we can determine the Transition Temperature as it records the heat flow inside (endothermic peak) or outside the sample (exothermic peak) when sample is being heated in as inert environment like Nitrogen or helium.

Yes

DSC is preferred over TGA for Tg. TGA will show Weight loss and residue obtained

• Determination of glass transition temperature by means of Differential Scanning Calorimetry (DSC) ASTM E1356
• Determination of glass transition temperature by means of Dynamic Mechanical Analysis (DMA) ASTM E1640-09
• Determination of glass transition temperature by means of Dilatometry (DIL)/Thermomechanical Analysis (TMA) ASTM E1545

Yes