Question

T_g of a polymer can be determined by

• A. NMR
• B. TEM
• C. DSC
• D. TGA

Hint:

DSC is also used to study melting point and crystallization behavior of polymers.

Answer 1

The Correct Option is C

Step 1: Understanding glass transition temperature (T_g).
The glass transition temperature is the temperature at which a polymer changes from a rigid, glassy state to a flexible, rubbery state. It is a thermal property related to molecular mobility.
Step 2: Technique used for T_g measurement.
Differential Scanning Calorimetry (DSC) measures changes in heat flow associated with thermal transitions in polymers, making it ideal for determining T_g.
Step 3: Analysis of options.
(A) NMR: Used for structural analysis, not thermal transitions.
(B) TEM: Used for morphological studies.
(C) DSC: Correct — Directly measures glass transition temperature.
(D) TGA: Measures weight loss, not T_g.
Step 4: Conclusion.
The glass transition temperature of a polymer is determined using DSC, hence option (C) is correct.

Answer 2

The question asks which technique is used to find the glass transition temperature (T_g) of a polymer. Since T_g is fundamentally a change in heat capacity as the polymer softens, the right technique must be one that tracks heat flow, not one that images structure or measures mass.

1. NMR: Nuclear Magnetic Resonance probes the local chemical environment and mobility of specific nuclei (like hydrogen or carbon), which is useful for structural elucidation and studying chain dynamics indirectly, but it does not directly record the heat-flow discontinuity that defines T_g.
2. TEM: Transmission Electron Microscopy produces images of internal morphology (crystallite size, phase domains) at very high resolution. It tells you what the material looks like inside, not how it responds thermally, so it cannot locate T_g.
3. DSC: Differential Scanning Calorimetry heats a sample and a reference at the same controlled rate and measures the difference in heat flow needed to keep them at the same temperature. At T_g, the polymer's heat capacity changes step-wise as chain segments gain mobility, showing up as a clear baseline shift on the DSC thermogram - this is the direct, standard signature of T_g.
4. TGA: Thermogravimetric Analysis tracks sample mass as temperature rises, which reveals decomposition, moisture loss, or filler content, but a glass transition involves no mass change at all, so TGA cannot detect it.

Only DSC is built to sense a heat-flow (not mass or structural) event, which is exactly what a glass transition is.

Therefore, the correct answer is DSC.