Question

Which of the following will have highest value of T_g?

• A. Polyethylene
• B. Polypropylene
• C. Cis polyisoprene
• D. Polystyrene

Hint:

Bulky side groups increase rigidity and raise the glass transition temperature.

Answer 1

The Correct Option is D

Step 1: Understanding glass transition temperature.
Glass transition temperature (T_g) depends on chain rigidity, bulky side groups, and intermolecular interactions. More rigid chains show higher T_g.
Step 2: Structural comparison.
Polystyrene contains bulky phenyl groups attached to the polymer backbone, which restrict molecular motion and increase chain stiffness compared to other polymers listed.
Step 3: Analysis of options.
(A) Polyethylene: Flexible chains with very low T_g.
(B) Polypropylene: Slightly higher T_g than polyethylene.
(C) Cis polyisoprene: Elastomer with low T_g.
(D) Polystyrene: Correct — Bulky phenyl groups lead to highest T_g.
Step 4: Conclusion.
Polystyrene has the highest glass transition temperature among the given polymers, so option (D) is correct.