Question

Which one of the following solvent environments will likely result in swelling of solid polystyrene?

• A. 0.1 M NaOH in H\textsubscript{2}O
• B. HCl (aq.) of pH = 6
• C. Distilled water
• D. Benzene

Hint:

Polymers swell most effectively in solvents with similar polarity or solubility parameters—non-polar polymers swell in non-polar solvents.

Answer 1

The Correct Option is D

Swelling of a polymer occurs when the solvent is chemically similar to the polymer—typically when both are non-polar or have similar solubility parameters. Polystyrene is a non-polar, hydrophobic polymer with strong affinity for aromatic, non-polar organic solvents. Options (A), (B), and (C): All are aqueous environments (water-based, polar). Polystyrene is hydrophobic and does not dissolve or swell in polar solvents, whether acidic, basic, or neutral. Thus, no swelling occurs.
Option (D): Benzene is a non-polar aromatic solvent very similar to polystyrene’s aromatic structure. Due to “like dissolves like”, benzene diffuses into the polymer matrix, causing significant swelling. Hence, benzene is the only environment where swelling will occur.