Question

What is the primary mechanical advantage of cross-linked polymers over linear polymers?

• A. Increased solubility
• B. Decreased thermal stability
• C. Enhanced elastic modulus
• D. Reduced electrical conductivity

Hint:

Cross-linking Polymers. Covalent bonds between chains create a network. Compared to linear polymers, cross-linking generally increases: Stiffness (Modulus), Strength, Hardness, Thermal Stability, Chemical Resistance. Decreases: Ductility, Solubility, Swelling.

Answer 1

The Correct Option is C

Linear polymers consist of long chains held together primarily by intermolecular forces (van der Waals).
Cross-linked polymers have covalent bonds formed between adjacent polymer chains, creating a network structure.
These cross-links significantly restrict the ability of polymer chains to slide past one another when stress is applied.
Mechanical consequences of cross-linking compared to the equivalent linear polymer: - Increased Elastic Modulus (Stiffness): The restricted chain movement makes the material resist deformation more strongly.
(Option 3) - Increased Strength: Higher stress required to cause yielding or fracture.
- Reduced Ductility/Increased Brittleness: Less ability to deform plastically.
- Decreased Solubility: Cross-links prevent chains from dissolving easily.
(Opposite of Option 1).
- Increased Thermal Stability: Cross-links often increase resistance to softening or degradation at higher temperatures.
(Opposite of Option 2).
Electrical conductivity (Option 4) is not primarily a mechanical property and its change upon cross-linking depends on the polymer type.
The primary *mechanical* advantage is the enhanced stiffness or elastic modulus.