Polymer Science

Step 1: Define the thermal transitions for a semi-crystalline polymer as temperature increases.
- D. Glass transition temperature (Tg): This is the temperature at which the amorphous (non-crystalline) regions of the polymer change from a rigid, glassy state to a more flexible, rubbery state. This is the first major transition that occurs upon heating.
- B. Crystallization temperature (Tc): When an amorphous polymer is heated above its Tg, the polymer chains gain mobility. If held at a certain temperature, they can arrange themselves into ordered, crystalline structures. This process is called crystallization. On a DSC scan of a polymer being cooled from a melt, Tc is the peak where heat is released as crystals form. When heating an amorphous sample, it can also appear as an exothermic peak after Tg. It logically occurs after Tg but before melting.
- A. Melting temperature (Tm): This is the temperature at which the crystalline regions of the polymer melt and the material becomes a viscous liquid. This requires more energy than the glass transition, so Tm is always higher than Tg.
- C. Degradation temperature (Td): This is the temperature at which the polymer's chemical bonds begin to break, and the material starts to decompose. This is a chemical change, not a physical transition, and it occurs at a much higher temperature than melting.

Step 2: Arrange these temperatures in ascending (increasing) order. The sequence is: Glass Transition Crystallization Melting Degradation.
This corresponds to the order D, B, A, C.