Effect of plasticisers: adding plasticisers to a polymer primarily increases which property by partially neutralising intermolecular attractions?

Introduction / Context:
Plasticisers are low-molecular-weight compounds blended into polymers (notably PVC) to improve flexibility and reduce brittleness. They interpose between chains, lowering secondary bonding and glass transition temperature (Tg).

Given Data / Assumptions:

• Plasticiser presence reduces chain–chain interactions.
• Lower Tg increases softness and flexibility.
• Tensile strength and chemical resistance usually decrease with heavy plasticisation.

Concept / Approach:
By spacing macromolecules and enhancing chain mobility, plasticisers shift the polymer into a rubbery regime at use temperature, dramatically boosting elongation and flexibility while typically compromising modulus and strength.

Step-by-Step Solution:
Identify the direct outcome of reduced intermolecular forces: increased flexibility.Reject strength and chemical resistance increases; these often drop.

Verification / Alternative check:
Mechanical data for plasticised PVC versus rigid PVC show lower modulus and tensile strength, higher elongation at break.

Why Other Options Are Wrong:
(a) and (b) contradict typical plasticiser effects; (d) overgeneralises.

Common Pitfalls:
Assuming any additive toughens a polymer; plasticisers soften and flexibilise rather than strengthen.

Final Answer:
Flexibility