Question

The glass transition temperature of polyethylene polymer is low in comparison with that of polypropylene fibre because of __________ molecular chain of polyethylene.

• A. asymmetric
• B. atactic
• C. symmetric
• D. rigid

Hint:

High symmetry and high flexibility in a polymer chain lead to a lower Glass Transition Temperature ($T_g$).

Answer 1

The Correct Option is C

Concept: The Glass Transition Temperature ($T_g$) is a measure of molecular mobility in the amorphous regions of a polymer.

Step 1: Structural Comparison.
Polyethylene consists of a simple repeating unit that is highly symmetric.

Step 2: The Effect of Symmetry on Mobility.
Because the polyethylene chain is symmetric and regular, the chains are extremely flexible. This high mobility allows the transition to occur at a very low temperature.

Step 3: Why Polypropylene is Different.
Polypropylene contains side groups that restrict molecular motion. This reduces flexibility and increases the $T_g$ compared to the symmetric polyethylene chain.