Question

Polymer crystals show a range of melting points in contrast to single melting point of crystals of small molecules, because \(\underline{\hspace{2cm}}\).

• A. there is an absence of intermolecular interactions
• B. there is an absence of long range ordering
• C. the polymer chains are not in thermodynamic equilibrium in a metastable state
• D. the melting behavior of polymer crystal is independent of sample thermal history

Hint:

Polymer crystals have a range of melting points due to the metastable states of polymer chains.

Answer 1

The Correct Option is C

Polymer crystals exhibit a range of melting points because the polymer chains are not in a well-defined thermodynamic equilibrium. In contrast to simple molecules, polymers have a complex molecular structure, and their crystalline regions can be in metastable states. This leads to variations in the melting points across the polymer crystals.

Step 1: Understand the behavior of polymer crystals.
Polymer crystals are not as regular as small molecular crystals, which results in a range of melting points. This is because the polymer chains, being large and flexible, can adopt different configurations that are not in equilibrium, thus leading to multiple melting points.

Step 2: Analyze the options.
- (A) absence of intermolecular interactions: Polymers do have intermolecular interactions, so this is incorrect.
- (B) absence of long-range ordering: This is not the main reason for the range of melting points. Polymers do exhibit some long-range ordering in the crystalline phase.
- (C) polymer chains are not in thermodynamic equilibrium in a metastable state: This is correct because the polymer chains can be in a metastable state, leading to a distribution of melting points.
- (D) melting behavior of polymer crystal is independent of sample thermal history: This is incorrect, as the thermal history does affect the melting behavior.

Step 3: Conclusion.
The reason for the range of melting points in polymer crystals is due to the polymer chains not being in thermodynamic equilibrium, leading to metastable states.

Final Answer: \text{(C) the polymer chains are not in thermodynamic equilibrium in a metastable state}